
Nucleic acid: an organic compound that contains the elements carbon, hydrogen, oxygen, nitrogen and phosphorus.
There are two types of Nucleic acids:
- Deoxyribonucleic acid (DNA)
- Ribonucleic acid (RNA).
These two nucleic acids are made of building blocks (or monomers) called nucleotides.
DNA is found in the form of chromosomes in the nucleus. Chromosomes carry the hereditary information in the form of genes.
DNA is also found inside the mitochondria and chloroplasts of eukaryotic cells. DNA that is found outside the nucleus is known as extranuclear DNA.
The structure of DNADNA is a double-stranded polynucleotide also called a double helix. . A polynucleotide chain is a very long molecule made up of a string of repeating, similar units called nucleotides.

DNA nucleotide consists of three parts:
- a deoxyribose sugar molecule
- a phosphate group
- a nitrogen-containing base.

There are four possible bases that can form part of a DNA nucleotide:
- adenine (A)
- thymine (T)
- guanine (G)
- cytosine (C)
These bases are grouped into two types, namely purines and pyrimidines.
Purines are larger molecules because
they consist of a double ring.
Pyrimidines are smaller molecules
because they consist of a single ring.
- Adenine and guanine are purine bases
- Thymine and cytosine are pyrimidine bases
Each DNA molecule consists of two polynucleotide chains (two parallel strands of nucleotides) that lie with the bases on each strand or chain facing each other.
Hydrogen bonds hold these two chains together to form a ladder-like structure.

The bases are always paired up in a specific way, in other words with a specific pyrimidine joined to a specific purine:
-adenine joins with thymine (joined by two hydrogen bonds)
-cytosine joins with guanine (joined by three hydrogen bonds).
How to recognise a DNA molecule
- Double-stranded molecule
- Contains the nitrogenous base thymine (T) instead of uracil (U)
- A always joins to T
- G always joins to C
Extranuclear DNA: DNA that is found outside the nucleus.
The discovery of DNA
Thoughout the 20th century, many scientists have tried to study the DNA. In the early 1950s two scientists, Rosalind Franklin and Maurice Wilkins, studied DNA using x-rays.
Maurice Wilkins and Rosalind Franklin produced an x-ray photograph of the DNA.
On the other hand two other researchers watson and crick were also studying the DNA structure. Maurice Wilkins decieved Rosalind Franklin and leaked the x-ray photogragh. This allowed watson and crick to work out the 3D structure of DNA.
They discovered that the structure was a double helix..
In 1962 Crick and Watson, along with Wilkins, received the Nobel Prize for their discovery. Sadly Rosalind had died four years earlier.';
DNA profiling
In the world, every human has unique DNA, excluding identical twins. This means that DNA can be used to identify an individual person just like a fingerprint.
DNA profiling is the process where a specific DNA pattern, called a profile, is obtained from a person or sample of
bodily tissue.
DNA profiling produces a pattern of dark bands that is unique to a person.

The picture above tells a story as you can see the knife was taken from a crime scene, Three suspects were found and only one is a suspect.
-Suspect (2) DNA pattern matchs the one on the crime scene because the black lines are align identically.
Uses for DNA profiling
- Forensic evidence to solve crime
- Find out whose the father (Paternity test)
- Identify diseases
- Matches lost family members
forensic: used in a court of law and/or with regard to solving a crime.
DNA Replications
DNA Replications is the process where by DNA makes an exact copy of itself
The DNA Replication process
- The double helix unwinds.
- Weak hydrogen bonds between nitrogenous bases break and two DNA strands unzip (separate).
- Each original DNA strand serves as a template on which its complement is built.
- Free nucleotides build a DNA strand onto each of the original two DNA strands by attaching to their complementary nitrogenous bases (A to T and C to G).
- This results in
two identical DNA
molecules. Each
molecule consists of
one original strand
and one new strand.
- The whole process takes place under the help of an enzyme called DNA polymerase

The significance of DNA replication
- Doubles the genetic material so it can be shared between the resulting daughter cells during cell division.
- Results in the formation of identical daughter cells during mitosis
Structure and types of RNA and their location in the cell
Structure of RNA
RNA molecule is a single-stranded polynucleotide. This means that it is made up of a single chain of nucleotides. RNA molecules are much shorter than DNA molecules.
The nucleotides of RNA differ slightly from those of DNA. An RNA nucleotide consists of
- a ribose sugar
- a phosphate group
- one of four bases: uracil, cytosine, guanine or adenine

Uracil is similar to thymine but uracil can only be found in the RNA molecule replacing the Thymine molecule
Types of RNA- Messenger RNA (mRNA)
- Ribosomal RNA (rRNA)
- Transfer RNA (tRNA)
During protein synthesis which you will learn later :
Messenger RNA (mRNA)
- Carries information about the amino acid sequence of a particular protein from the DNA in the nucleus, to the ribosome where the protein will be made.
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
Location of RNA in the cell
- RNA is found in the nucleus of the cell where it is made by DNA
- RNA is also found in the cytoplasm (tRNA and mRNA)
- rRNA is found forming the ribosomes in the chloroplasts of plant cells and in the mitochondria of plant and animal cells.
The difference between DNA and RNA

DNA
- Double-stranded molecule
- Contains deoxyribose (sugar)
- Contains the nitrogenous base,thymine
- Larger molecule
RNA
- Single-stranded molecule
- Contains ribose (sugar)
- Contains the nitrogenous base,uracil
- Small molecule
Protein synthesis
Protein synthesis is the process by which proteins are made.
- Protein molecules are long chains of amino acids bonded together by peptide bonds.
- 20 different amino acids are used to make proteins.
There are two main processes involved in making of protein, namely transcription and translation.
- Transcription
- Translation


How the process takes place
Transcription:Takes place in the nucleus- DNA unwinds and splits.
- One DNA strand acts as a template for forming mRNA.
- Free nucleotides arrange to form mRNA according to the DNA template. This process is called transcription.
- The mRNA leaves the nucleus. Stage B now takes place when mRNA in the cytoplasm attaches to the ribosome.
- Each tRNA brings a specific amino acid to the mRNA. This is called translation.
- The amino acids are joined together by peptide bonds to form a particular protein.

Meiosis
What is meiosis ?
- Meiosis is a type of cell division whereby a diploid cell (somatic cell) divides to form four dissimilar haploid cells (sex cells).
- Diploid cells have two sets of chromosomes, where each chromosome has a homologous partner. Haploid cells only have one set of chromosomes.
- Chromosomes in haploid cells have no homologous partners.
- Before meiosis begins (during interphase), DNA replication takes place. The result is two sets of chromosomes consisting of two identical chromatids joined together with a centromere.

The process of meiosis in animal cells
Meiosis is the type of cell division used to produce gametes or sex cells (sperm and eggs).
- A cell undergoing meiosis will divide twice – the first division is meiosis 1 and the second is meiosis 2.
In the first meiotic division, the number of cells is doubled, but the number of chromosomes is not. This results in half as many chromosomes per cell.
- In the second meiotic division, the number of chromosomes does not get reduced.
Meiosis I
- Interphase 1
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1
- During interphase 1 , DNA replication takes places as the chromosomes replicate.
- Each chromosome consists of two genetically identical sister chromatids attached at their centromeres.

- Chromosomes shorten and become visible as two chromatids joined by a centromere.
- Homologous pairs of chromosomes are now visible.
- The nuclear membrane and nucleolus disappear.
- The spindle starts to form.
- Chromatids from each homologous pair touch. The point where they touch is called a chiasma.
- DNA is crossed over (swopped) at the chiasma.
- The spindle continues to form.

- The spindle extends across the whole cell.
- The homologous chromosomes line up along the equator of the spindle in their homologous pairs.
- One chromosome of each pair lies on either side of the equator.
- The centromere of each chromosome attaches to the spindle fibres.

- The spindle fibres shorten and pull each chromosome of each chromosome pair to opposite poles of the cell.

- The chromosomes reach the poles of the cell.
- Each pole has half the number of chromosomes present in the original cell.
- The cell membrane constricts and divides the cytoplasm in half to form two cells.

Meiosis II
- Prophase 2
- Metaphase 2
- Anaphase 2
- Telophase 2

- Each cell formed during meiosis I now divides again.
- A spindle forms in each of the new cells
- Individual chromosomes line up at the equator of each cell, with the centromeres attached to the spindle fibres.
- The spindle fibres start to contract.
- The centromeres split and daughter chromosomes/ chromatids are pulled to the opposite poles of each cell.
- The daughter chromosomes/chromatids reach the poles and a new nucleus forms.
- The cell membrane of each cell constricts and the cytoplasm divides into two cells.
- Four haploid daughter cells are formed.
- Each daughter cell has half the number of chromosomes of the original cell.
- The daughter cells are genetically different from each other.
The significance of meiosis
There are two reasons why meiosis is important:
- It reduces the number of chromosomes by half, in other words from diploid to haploid.
- Brings about variation

Differences between meiosis I and meiosis II
meiosis I
- The chromosomes arrange at the equator of the cell in homologous pairs.
- Whole chromosomes move to opposite poles of the cell.
- Two cells form at the end of this division.
- The chromosome number is halved during meiosis I.
- Crossing over takes place.
meiosis II
- Chromosomes line up at the equator of the cell individually.
- Daughter chromosomes/chromatids move to opposite poles of the cell.
- Four cells are formed at the end of this division
- The chromosome number remains the same during meiosis II.
- Crossing over does not take place.

Mitosis
Mitosis is division of the nucleus. During mitosis, the nucleus of a cell divides to produce two daughter nuclei. Each daughter nucleus has the same number and type of chromosomes as the parent nucleus.
Mitosis takes place when an organism needs to grow, replace damaged tissues or reproduce asexually. Although mitosis is a continuous process, it is divided into four stages
The differences between Mitosis and meiosis
Mitosis
- Mitosis occurs continuously in the body or somatic cells
- Mitosis had one cell division
- During prophase crossing over doesn't take place
- Exchanging of genetic material doesn't take place
- Two daughter cells are formed
Meiosis
- Meiosis occurs in the germ cells during the process of gametogenesis
- Meiosis has two cell divisions
- During prophase crossing takes places
- Exchanging of genetic material does take place
- Four daughter cells are formed
Similarities
- DNA replication takes places in both divisions
- Meosis 2 is similar to meiosis
- Both Mitosis and Meiosis go through interphase, prophase, metaphase, anaphase and telophase
- Both use spindle fibers to separate chromtids from each other during metaphase
How meiosis results in genetic variation of gametes
The two events of meiosis that result in genetic variation of the gametes are crossing over and random segregation
Crossing over- During prophase 1 chromosome come together and exchange genetic material bringing about variation

- During metaphase 1 and 2 Chromosomes align at the equator randomly bringing about variation

abnormal meiosis
If meiosis does not take place normally, the gametes produced may have chromosomal abnormalities such as a change in the number or the structure of the chromosomes. Chromosomal abnormalities may result in different genetic disorders, for example Down syndrome in humans.
Non-disjunction
- Non-disjunction is a type of error that could happen during meiosis
- Non-disjunction occurs when homologous chromosomes do not separate at Anaphase I or the sister chromatids do not separate at Anaphase II.
- As a result of non-disjunction, the gametes produced have too many or too few chromosomes.

Human disorders caused by abnormal meiosis
A person with a chromosomal abnormality may have a specific syndrome that is characteristic of the disorder.
- Scientists can predict the specific type of disorder by looking at the person’s karyotype to see if there are any extra or missing chromosomes.
Down syndrome
Down syndrome is one of the most frequently occurring chromosomal abnormalities. The syndrome is usually the result of an extra chromosome 21, so that each body cell has three chromosomes 21 (Trisomy 21) and a total of 47 chromosomes


Charateristics
- small eyes
- stocky body
- distinct facial
- big forehead
What is fertilisation
Fertilisation : is the fusion of a sperm cell and an egg cell to form a diploid zygote
External fertilisation
- Fertilisation that takes place outside the females body, usually in water
- The male and female gametes are released into the water.
- The sperm cells either swim towards the egg or are directed towards the egg.

Advantages |
---|
• Better chance of fertilisation taking place |
• Good chance for some eggs to survive since many eggs are released. |
Disadvantages |
• Requires water for fertilisation to take place. |
• Not all fertilised eggs will survive. |
Internal fertilisation
- Internal fertilisation : Is a type of fertilisation that takes place inside the females body.
- Usually the male inserts the reproductive organ into the female and releases sperm that swim up the females, reproductive organ to the ovaries.

Advantages |
---|
• Gametes have a better chance of surviving |
• 24 hour protection |
Disadvantages |
• Less chance of fertilisation taking place. |
• Complication of fertilisation can take place. |
Overview
- Once an egg cell has been successfully fertilised, a zygote is formed. The zygote develops into an embryo.
- There are three possible ways in which the needs of the developing embryo can be met, namely through ovipary, vivipary and ovovivipary.
Ovipary
- Ovipary refers to animals that lay eggs.
- Oviparous animals lay eggs after the ova (egg cells) have been fertilised inside the female’s body

Vivipary
- In these animals, the young develop inside the mother and are protected by her body during their development

Ovovivipary
In ovovivipary, eggs are produced and fertilised, but stay inside the mother’s body


Functions
- Amnion : Provides protection to the embryo
- Allantois : Collects nitrogenous wastes and gas exchange
- Chorion :Gaseous exchange
- Yolk sac : Provides food and nutrients to the embryo
- Shell :Regulates the eggs temperature and allows for gaseous exchange
Precocial and altricial development
Altricial development
- Animals born dependent of their parents. In other words cannot survive on their own
Characterisitics after they born
- Cannot feed themselves
- Cannot open their eyes
- Cannot move on their own
- Have no feathers when born
Precocial development
- Animals born independent of their parents. In other words they can survive on their own
Characterisitics after they born
- Can move on their own
- eyes are opened when born
- They are independent of their parents
Parental Care
Parental care involves providing a nurturing and protected environment in which the young can grow and develop. Because of the helplessness of their young, this behaviour is better developed in altricial species.
Structure of the male reproductive system


Functions of the male reproductive system
- Vas deferens :A gland that secretes fluid that provides food source to sperm
- Prostate gland :Produces an alkaline fluid that neutralises the acids produced in the vagina, which would kill sperm cells
- Urethra :Transports urine and semen out of the body at certain times
- Epididymis :Sperm cells mature and are stored here
- Penis :Enters the females reproductive organ during intercourse
- Ureter :Stores sperms until they mature and are ready to be released
- Seminal vesicle : Secretes an alkaline fluid which neutralise the acid found in the vagina, that would kill the sperm
- Erectile tissueA tissue that fills up with blood during an erection
- Scrotum :
- Regulates the temperature for optimal sperm production
- Provides protection to the sperm
- TestisProduces sperm cells and the hormone testosterone

Functions of testosterone
- Testosterone is a hormone that is secreted by the Cells of Leydig.
- Development of male secondary sexual characteristics, such as beard, pubic hair, deep voice and a muscular body.
- Stimulates the maturation of sperm cells
Seminiferous tubules
Seminferous tubules have specialised cells called Sertoli cells which provide food(nutrients) to the spermatids/sperm.
Sperm cell

- Acrosome: Contains enzymes to digest wall of egg cell for fertilisation
- Nucleus: Contains 23 chromosomes
- Mitochondria: Provide energy for swimming
- Tail: Used for swimming

Functions of the female reproductive system
- Fallopian tube: Connects the ovaries to the uterus, transports egg cells from the ovary; it is the site of fertilisation
- >Ovary :Produces egg cells, secretes progesterone and oestrogen
- Vagina :Receives the penis and semen during sexual intercourse; it is the passage through which the baby is born
- Uterus :Carries the embryo and foetus during pregnancy
- Endometrium :Inner lining of uterus; place where the embryo implants and the placenta forms
- Cervix : Lower, narrow part of uterus. It stretches to allow the baby through during childbirth
Puberty
- Puberty refers to the age at which girls and boys become sexually mature.
Signs in girls
- Increased size in breast
- growth of hair in private areas
- growth of hips
Signs in boys
- Increased voice bass
- Facial hair
- growth of hair in private areas
Gametogenesis
- Gametogenesis refers to the formation of sex gametes (sperm and egg).
Spermatogenesis
- Spermatogenesis refers to the process in which sperms/spermatozoa are formed and produced.
- Another name for sperm is spermatozoa
How Spermatogenesis takes place
- Cells of the germinal epithelium undergo meiosis
- Then the cells produces haploid spermatids
- Then the spermatids mature and become a spermatozoan

function of the spermatozoa
- Acrosome : Contains enzymes to digest wall of egg cell for fertilisation
- Nucleus : Contains 23 chromosomes
- Mitochondria : Provide energy for swimming
- Tail : Used for swimming
Oogenesis
- Oogenesis refers to the process in which ovum are formed and produced.
- Another name for ovum is ova
How Oogenesis takes place
- Cell of the germinal epithelium undergo meiosis to form numerous follicles
- One of the cells enlarges and undergoes meiosis
- One cell then matures to form an ovum

The menstrual Cycle - Hormonal Control
The menutrual cycle refers to the changes that occur in the ovary and uterus of a female over a period of 28 days, for the preparation of fertilisation.
There are two cycle that make up the menstrual cycle
- Ovarian cycle
- Uterine cycle
The Ovarian cycle and Ovulation
The ovarian cycle describes what happens inside the ovary as the ovum develops inside the the Graffian follicle, which then releases the ovum to become a corpus luteum.
How it takes place ?
- FSH (Follicle stimulating Hormone ) Produced by (Hypophysis/pituitary gland)
- Causes the follice in the ovary to transform into a Graffian follice with a mature ovum
- A Graffian follicle produces a hormone called Oestrogen
- Which prepares the uterus for attaching the fertilised ovum
- After 4 weeks (28 days), 0vulation takes place where by the graffian follicle ruptures/breaks open and releases an ovum
- The ovum is then carried by the funnel of the fallopian tube.
- LH (Luteinising hormone) Produced by the (Hypophysis/pituitary gland) helps convert the ruptured graffian follicle into a Corpus luteum.
- Corpus luteum secretes the hormone Progesterone: which maintains pregnancy.
- When fertilisation takes place Corpus luteum continues to secretes progesterone.
- When fertilisation doesn't take place the Corpus luteum degenerates and the progestrone production level decrease
- The unfertilized ovum then passes down the uterus and levels the body with blood also
- This process is called Menstruation.
Recap
- Hypophysis or Pituitary gland Produces : FSH and LH
- FSH causes a follice in the ovary to become a Graffian follice
- Graffian follice Secretes : Oestrogen (Which prepares the wall of the uterus for the attachment of the ovum)
- After (28 days) Graffian follice raputures and releases a mature ovum (Ovulation)
- LH causes the raputured Graffian follice to become a corpus luteum
- Corpus luteum Secretes : Progesterone (Which maintains pregnancy)
The Uterine cycle and Menstruation
- During menstruation, the endomertrium lining comes off as the menstrual period, as we notice bleeding
- The menstrual period usually lasts for about 4 to 5 days.
- menstruation takes place about 14 days, this means that menstruation takes place after day 28
- The next ovum is then released about 14 days after menstruation.
- When a women stops releasing ova, she stops menstruating. This is called menopause and occurs between the ages of 45 and 55

Fertilisation and Development to Blastocyst Stage

- During sexual intercourse the male inserts the penis into the female and release sperm inside the vagina
- The sperm then swims up the uterus into the fallopian tube
- If there is any ovum present the sperm penetrates and fertilise the ovum resulting in a diploid zygote
- Remember the sperm has 23 pairs of chromosomes and the ovum has 23 pairs of chromosomes (23 + 23 = 46)
- The zygote then has 46 pairs of chromosomes and genetic material from both parents
- Then the zygote divides by mitosis to form a morula
- The morula further divides by mitosis to form a hollow ball of cells called the blastocyst.

Development into an Embryo
- The blastocyst the develops into an embryo
- The embryo becomes attached to the endometrium wall of the uterus. (This is called implantation).
Gestation
Gestation is the process during which the embryo develops into a foetus to a baby. (Pregnancy)
Foetus and Role of the placenta


Role of the placenta
- Attaches the embryo to the mother
- Moves dissolved food from the mother to the foetus
- Moves oxygen from mother to the foetus and carbon dioxide from foetus to mother
- Moves nitrogenous waste from the from the foetus to the mohter
- Secrets Progestrone after 12 weeks to maintain pregnancy
Umbilical cord
- The umbilical cord attaches the foetus to the placenta.
- An umbilical cord contains :
- Umbilical artery : Carries deoxygenated blood with nitrogenous wastes from the embryo to the placenta
- Umbilical vein : Carries oxygenated blood with dissolved food from the placenta to the foetus.
- Umbilical artery : Carries deoxygenated blood with nitrogenous wastes from the embryo to the placenta
Amniotic fluid
- Acts as a shock absorber (Protects the embryo against mechanicsl injury)
- Prevents dehydration of the embryo
- Allows the foetus to growth smoothly
- Regulates the foetus temperature
- Acts as a barrier, stop sperm getting into the vagina Female condom
- It prevents fertilised ova/embryos from becoming attached to the uterine wall
Diaphragm:
- Acts as a barrier as it covers the cervical opening and prevents sperm from entering the uterus
Contraceptive pill:
- Contain artifically produced hormones which prevents the production of ova/ovulation
withdrwal:
- The penis is taken out of the vagina before ejaculation
Rhythm:
- Sexual intercourse is avoided three to four days before and after ovulation.
Condom:
Key concepts
The following are very important terminolgies to understand for for Genetics
- Gene : A small portion of DNA coding for a particular characteristic.
- Alleles : Different forms of a gene which occur at the same locus (position) on homologous chromosomes.
- Heredity : The transmission of characteristics from parents to their offspring.
- Inheritance : refers to the set of characteristics that have been passed from parents to offspring.
- Genotype : Genetic composition (makeup) of an organism.
- Phenotype : The physical appearance of an organism determined by the genotype, e.g. tall, short.
- Dominant allele : An allele that is expressed (shown) in the phenotype when found in the heterozygous (Tt) and homozygous (TT) condition.
- Recessive allele : An allele that is masked (not shown) in the phenotype when found in the heterozygous (Tt) condition. It is only expressed in the homozygous (tt) condition
- Heterozygous : Two different alleles for a particular characteristic, e.g. Tt.
- Homozygous : Two identical alleles for a particular characteristic, e.g. TT or tt.
- Monohybrid cross : Only one characteristic or trait is being shown in the genetic cross.
- Multiple alleles : More than two alternative forms of a gene at the same locus.
- Polygenic inheritance : A characteristic that is controlled by two or more genes which may be found on the same or different chromosomes
- Sex-linked characteristics : Characteristics or traits that are carried on the sex chromosomes.
- Karyotype : The number, shape and arrangement of all the chromosomes in the nucleus of a somatic cell.
- Cloning : Process by which genetically identical organisms are formed using biotechnology
- Genetic modification : The manipulation of the genetic material of an organism to get desired changes.
- Human genome : The mapping of the exact position of all the genes in all the chromosomes of a human.
Monohybrid Crosses
A monohybrid cross refers to a cross where only one set of characteristic is inherited.
E.g What would happen if you cross a domiante Tall plant with a recessive short plant
Since the Tall plant is dominat it will have the initials (TT)
Since the Short plant is recessive it will have the initials (tt)
T | t | |
---|---|---|
t | Tt | Tt |
t | Tt | tt |
F1
Genotype = 3(Tt) 1(tt)
Phenotype = 3(Tall) 1(short)
Percentage = 3/1 =25%(short) 75%(Tall)
Another example: A heterozygous red flower plant is crossed with a white-flower plant
Since the red flower is heterozygous it will have the initials(Rr) and the white flower will have the initials(rr) because its recessive
Key R=red x r=white
P1
Genotype = Rr x rr
Phenotype = Red flower x White flower
meiosis
G1
R | r | |
---|---|---|
r | Rr | Rr |
r | Rr | rr |
F1
Genotype = 3(Rr) 1(rr)
Phenotype = 3(Red) 1(white)
Percental = 3/1 =25%(Red) 75%(white)
Dihybrid Crosses
A Dihybrid cross refers to a cross where two set of
characteristic are inherited.
Remember with a dihybrid cross we have two separate traits and we want
to show that these traits undergo independent assortment one of mendels
laws.
To begin will start with a Key.
TT = tall
Tt = tall
tt = short
RR = red
Rr = red
rr = yellow
To Solve a dihybrid cross you have to start with a key to show
you understand the pattern.
After you do the cross.
For example : Heterzyous tall plant and red seeds with another x
Heterzyous tall plant and red seeds.
So the Genotype will be ( TtRr x TtRr)
So now will have to draw a 8 by 8 plate square.
Now we need to determine what allels each of the plants need to put
in their gametes.
TR
Tr
tR
tr
TR
TTRR
TTRr
TtRR
TtRr
Tr
TTRr
TTrr
TtRr
Ttrr
tR
TtRR
TtRr
ttRR
ttRr
tr
TtRr
Ttrr
ttRr
ttrr
Do you see the pattern...
TR
Tr
tR
tr
TR
TTRR
TTRr
TtRR
TtRr
Tr
TTRr
TTrr
TtRr
Ttrr
tR
TtRR
TtRr
ttRR
ttRr
tr
TtRr
Ttrr
ttRr
ttrr
Genotype
- TTRR (1/16)
- TTRr (2/16)
- TTrr (1/16)
- TtRr (2/16)
- TtRr (4/16)
- Ttrr (2/16)
- ttRR (1/16)
- ttRr (2/16)
- ttrr (1/16)
Phenotype
- (9/16) Tall and red
- (3/16) Tall and yellow
- (3/16) Short and red
- (1/16) Short and yellow
Ration :9 : 3 : 3 : 1
Mendel's Experiments
Gregor Mendel, was an Austrian monk who carried out breeding experiments with garden peas from 1857 to 1864
Monks had a lot of time on there hands and mendel spent his time crossing pea plants. As he did this over and over again, he noticed some patterns
to the inheritance of traits from one set of pea plants to the next. By carefully analyzing his pea plant numbers (he was really good at math), he
discovered three laws.
Mendel's Laws are as follows
- The Law of Dominance
- The Law of Segregation
- The Law of Independent Assortment
The Law of Dominance
The Law of dominance states that only one trait in a pair will be dominate and therefor show up in the Phenotype unless the pairs are recessive
e.g Tall(T) x Short(t)
= Tall(Tt)
The Law of Segregation
The Law of Segregation states that members of a pair of homologous chromosomes separate during the formation of gametes and are distributed to different
gametes so that every gamete receives only one member of the pair
The Law of independent Assortment
The Law of independent Assortment states that each member of a pair of homologous chromosomes separates independently of the members of other pairs so the results are random
Three types of Dominance
- Complete dominance
- Incomplete dominance
- Co-dominance
Complete dominance
A genetic cross where only one allele is dominant over the other allele and therefore only the dominant one is expressed in the phenotype.
Example :
P1
Genotype = RR x rr
Phenotype = Red x white
meiosis
G1
R
R
r
Rr
Rr
r
Rr
Rr
F1
Genotype = 4(Rr)
Phenotype = 4(Red)
Incomplete dominance
A genetic cross where none of the allele's are dominance over the other and therefore none of them are expressed in the phenotype.
Example :
P1
Genotype = RR x rr
Phenotype = Red x white
meiosis
G1
R
R
W
RW
RW
W
RW
RW
F1
Genotype = 4(RW)
Phenotype = 4(Pink)
RR +
WW =
RW
Co-dominance
A genetic cross where both of the alleles are dominant over each other and are therefore are both expressed in the phenotype.
Example :
P1
Genotype = RR x rr
Phenotype = Red x white
meiosis
G1
R
R
W
RW
RW
W
RW
RW
F1
Genotype = 4(RW)
Phenotype = 4(Equal colours both red and white)
RR +
WW =
RW
Blood types
In humans you find only three types of blood groups
Blood type can also be used to determine parentage but since many people have the same blood group it not be useful
• A
• B
• O
An individual can only have two of these alleles making up his/her genotype
The i alleles is recessive to the |A , |B. These alleles are co-dominant
Understanding these group types
|A and |B = are co-dominant
|A is dominant = over i
|B is dominant = over i
ii are just two recessive alleles
Example : Crossing a homozygous parent with blood type A and heterozygous blood type B parent
P1
Genotype = |A |A x |B i
Phenotype = Homozygous A blood type x Heterozygous B blood type
meiosis
G1
|A
|A
|B
|A |B
|A |B
i
|A i
|A i
F1
Genotype = 2(|A |B) 2(|A i)
Phenotype = 2(With AB blood type) and 2(with A blood type)
Mutations
Mutations means sudden, changes in the genetic code of an organism which can be inherited.
Causes of mutations
Mutations occur suddently and randomly and may be caused by many environmental agents such as X-rays, cosmic rays, ultra-violet radiation and certain chemicals.
Where does mutation occur
- Somatic cells and sex cells
- When they occur in somatic cells they results in disorders such as cancer
- When they occur in sex cells they can be inherited
Two Types of Mutations
- Gene mutations
- Chromosomal Aberrations
Gene mutations
A gene mutation refers to a change in the structure of a gene as a result of a change in the DNA sequence.
Types of Gene mutations
Point Mutations
- In point mutation, there is a change in a single base pair in the DNA molecule at just one point (i.e. a single base pair is replaced by another base pair).
Frame-shift Mutations
- A single base pair may be inserted or deleted from the DNA molecule.
Chromosomal Aberrations/Chromosomal Mutations
- Chromosomal Aberrations refers to changes in the normal structure or number of chromosomes
Types of Chromosomal Aberrations
- Deletions : In Which a section of a chromatid is simply lost
- Duplications : In which a section of a chromatid is doubled
- Inversions : In which a section of a chromatid gets turned
- Translocations : In which a part of the chromatid amy break off and join a non-homologous chromosome.
Effects of mutations
You find Harmful mutations and Harmless mutations
Harmful Mutations
Harmful mutations are also called lethal mutations, the mutated organism dies along with the mutations, so the characteristic is not past on to the next generation.
Harmless Mutations
There are two types of harmless mutations
- Neutral mutations
- Advantageous mutations
Neutral mutations
Neutral mutations have no effect on the organism they affect, meaning it normal to have the mutations.
Advantageous mutations
Advantageous mutations are actually an advantage to the organism they affect meaning that they may offer special abililties which normal organism may be incapable of doing.
Sex Determination in Humans
As you know XX represents a Female and XY represents a Male
Males have a single X-chromosome + (22 pairs of autosomes)
Autosomes: All chromosomes besides the sex chromosome
Females have two X-chromosomes + (22 pairs of autosomes)
How to determine sex in humans
P1
Genotype = XX x XY
Phenotype = Female x Male
meiosis
G1
X
X
X
XX
XX
Y
XY
XY
F1
Genotype = 2(XX) 2(XY)
Phenotype = 2(Females) 2(Males)
Percentage = 50%(female) 50%(male)
This means that there is a 50:50 chances that the offsprings will be male or female.
Now representing the inheritance of sex-linked charateristics in a genetic cross
Lets make an example of haemophilia ,a genetic disorder which affects mostly males
Key note to understand
Females
XH XH = normal blood (Homozygous normal female)
Xh X h = haemophilia (Homozygous haemophilia female)
XH Xh = normal blood (carrier)
(Heterzygous normal female)
Males
XH Y = normal blood
Xh Y = haemophilia
HH doesn't have haemophilia and not even a carrier
Hh doesn't have haemophilia but a carrier
hh has haemophilia and also a carrier
In Males the Y-Chromosome will never be normal and carriers
Example: What will happen when a Heterzygous normal Female cross with a normal male
XH
Xh
XH
XH XH
XH Xh
Y
XH Y
Xh Y
F1
Genotype
XH XH
XH Xh
XH Y
Xh Y
Phenotype
1 = Normal blood female
1 = Normal blood (carrier) female
1 = Normal blood male
1 = haemophilia male
Genetic disorders caused by Mutations
The following disorders are also known as sex-linked disease as they are inherited.
- Down syndrome
- Sickle-cell anaemia
- Haemophilia
- Albinism
Down syndrome
Causes
Down syndrome is cause by an extra copy of chromosome 21. They are 3 copies instead of 2. Remembers this also is called trisomy 21.
Symptoms
- Mental retardation
- Hearing loss
- Decreased muscle tone
- Upwardly slanting eyes
- Small mouth
- Abnormal ear shape
- Small nose
Sicle-cell anaemia
Causes
Sickle-cell anaemia is caused by a mutant allele on chromosome number 11. Sicle-cell cause the red blood corpuscle to become sickle shaped.
Symptoms
- Redued blood supply
- Damage to organs such as the spleen
- Damageed parts of the brain
- suddent pains
Treatment
- Blood transfusions and drugs may help to reduce pain.
- Bone marrow transplant
Haemophilia
A person suffering from haemophilia has hard time clotting his/her blood which may result in mass blood loss
Causes
Its caused by a recessive allele on the X-chromosome
Symptoms
- Blood does not clot well
- Internal bleeding at joints which may lead to arthritis
- Bleeding to death without treatment
Treatment
- Injection of purified clotting agents extracted from human blood plasma
Albinism
A person who is suffering from albinism lacks a pigment called melanin.
Causes
Caused by a mutation of a gene on the X-Chromosome.
Symptoms
- Poor vision
- light skin which gets sunburns very easily
- Skin highly susceptible to skin cancer
Treatment
- Sunscreen to reduce skin burns
- eye glass to enhance vision
Genetic Engineering
Genetic engineering, also called genetic modification is to change the characteristics of an organism by manipulating its genetic material.
Cloning is a type genetic engineering, where the aim is to duplicate the genes of an existing individual so that an identical set is inside an egg.
The use of stem cells to treat disease, like cloning, is alos a type of engineering but is not the same as true genetic manipulation.
Genetically Modified Organisms
- The first genetically modified organisms were bacteria in 1973
- Plant can also be modified so that they become bigger and resistant to dieases.
Arguments for genetic modification
- Pest resistant and drought resistant plants
- Cheaper production of medication or other resources
- Increased crop yield's therefor increased food security
Arguments against genetic modification
- Expensive
- Interfering with nature
- unkown long term effects to human health
Pedigree Diagrams
A pedigree diagram is used to study the inheritance of characteristics in
a family over a number of generations. A pedigree diagram is also called
a family tree.
Steps when interpreting pedigree diagrams:
- Step 1 : Study any key and opening statement/s and look for dominant and recessive
characteristics and phenotypes.
- Step 2 : Write in the phenotypes of all the individuals as given in the problem.
- Step 3 : Fill in the genotype of all the individuals with the recessive condition – it must have two
recessive alleles (two lower case letters, e.g. ff).
- Step 4 : For every individual in the diagram that has the recessive condition, it means that each
allele was obtained from each of the parents. Work backwards and fill in one recessive
allele for each parent.
- Step 5 : If the parents showed the dominant characteristic, fill in the second letter which
represents the dominant allele (a capital letter, e.g. F).
- Step 6 : Any other individual showing the dominant characteristic will most likely be homozygous
dominant (FF) or heterozygous dominant (Ff).
Now lets do an example
Brown eye colour (B) is
dominant over blue eye colour (b).
Our pedigree
Genetic counselling
Couples with a risk of giving birth to children with genetic diseases can undergo genetic counselling
to enable them to make informed decisions on whether they want to have
children or not.
Benefits of genetic counselling
- To be given advice on the risk of transferring the defective gene/
to find the probability of passing on the defective gene to the
offspring
- To be given an explanation of the procedure involved in DNA
testing
- To be given an explanation of the results of DNA testing
The human nervous system
Nervous Tissue
Nervers are made up of nerver fibres held togther by connective tissues.
The nerver fibres on the other hand are made up of specialized nerver cells
called Neurons.
Neurons are specialised cells which connect the brain and spinal cord to
all other parts of the body.
Three types of Neurons
- Sensory neurons
- Motor neurons
- Connector neurons/interneurons
Sensory nenron
- Carries impulses from the receptors to the central nevrous system
Motor nenron
- Carries impulses from the central nervous system to the effectors
Connector nenron
- Carries impulses inside the central nervous system from a sensory neuron to a motor nenron
Parts of the neuron definination
- Dendrite: Transmits impulses towards
the cell body of the neuron
- Axon: Transmits impulses away from
the cell body of the neuron
- Myelin sheath: provides electrical insulation and helps to speed up up the transmission of impulses.
Synapse
A microscopic gap between the axon terminals of one neuron and the dendrite of another.
Neurotransmiitters
Carries nerve impulses from one dendrite to another.
The main parts of the Nervous System
The Nervous system is divide into two main parts
- Central nervous system
- Peripheral nervous system
Central nervous system includes
- The Brain
- Spinal Cord
Peripheral nervous system
Is made up of all the nerves outside the central nervous system
Its further sub-divided into
- Somatic nervous system
- Autonomic nervous system
Somatic nervous system
Includes parts of the nerves system that enables the body to react to changes in the external environment.
Autonomic nervou system
Includes parts of the nerves system that control the internal enivornment. e.g (actions of sweating, and the heart and breathing rates.)
The Central Nervous System
The central nervous system consists of the brain and the spinal cord
The structure and functions of The Brain
Cerebrum
- Controls voluntary
actions
- Receives and
interprets sensations
from sense organs
- Higher thought
processes
Medulla oblongata
- Transmits nerve
impulses between the
spinal cord and the
brainr.
- Controls involuntary
actions such as
heartbeat and
breathing
Hypothalamus
Control centre for
hunger, thirst, sleep,
body temperature
and emotions
Cerebellum
- Coordinates
all voluntary
movements
- Controls muscle
tension to
maintain balance
The Spinal Cord
- The spinal cord is an elongated cylinder-like structure running in the vertebral canal formed by successive vertebrae.
- The spinal cord is protected by the meninges
- The spinal cord consists of white matter on the outside and grey matter on the inside.
Functions of the spinal cord
- It conducts impulses between the brain and the receptors and effectors
- It serves as a reflex centre for actions such as blinking, sneezing, coughing and knee jerk
Reflex action and Reflex arc
A reflex action is a quick, automatic response to a stimulus received by an organ or other receptor.
The reflex arc is the path along which an impulse is transmitted to bring
about a response to a stimulus during a reflex action.
Reflex arc
The path taken by an impulse to bring about a response to a stimulus during a reflex action.
The path of a reflex arc:
Receptor (A) → Sensory neuron (B) → Interneuron (C) → Motor neuron (D) → Effector (E)
The reflex action
- Receptor: A structure which receives a
stimulus and converts it into an impulse
(the heat sensor of the finger feels burn)
- Sensory
neuron:
Carries the
impulse from
the receptor to
the spinal cord
- Effector:
A structure
which
produces the
reaction (the
muscles in the
finger contract
and the finger
is pulled
away)
- Interneuron: Carries the impulse
from sensory neuron to the motor
neuron in the spinal cord
- Motor neuron: Carries
the impulse from the
spinal cord to the
effectors
Disorders of the central nervous system
Alzheimer's disease
Is a diseases that occurs when the nerve tissue within the brain appears to waste away.
Symptoms
- Memory loss
- Confusion
Multiple sclerosis
When the bodys own immune system attacks and destroys the myelin sheath causing a disorder
called multiple sclerosis.
Symptoms
- Physical disabilities
- Mental disabilities
Effects of drugs
Dagga (Marijuana or Cannabis)
- Affects the parts of the barin that control emotions ,memory and judgment
- Weaken short-term memory and block information from becoming save into long trem memory
Heroin
- Gives an immediate 'rush ' of pleasure but leaves the brain in a 'fog' for many hours afterwards
- Difficulty in differentiating reality and fantasy
Ecstasy
- Difficulty in differentiating between reality and fantasy
- Problems in concentration
Tik
- Paranoia ,anxiety,fearfulness and exhaustion
- Memory loss ,mood swings,wild rages
Alcohol
- Impairs judgment and leads to to memory lapses
- Can damage every organ in the body,including the brain
Cocaine
- Loss of interest in many areas of life ,including school ,sports,family ,and friends
- paranoia and anxiety
The human eye
Structure of the ear and function
- Retina : Contains the light-senstive receptor cell
- Sclera: The tough white outer coat ,which protects the eye against damage
- Choroid: Reduces reflection
,Supplys cells with nutrients and oxygen
- Yellow spot : Has the greatest number of cones, this area offers the clearest image
- Optic nerve: Carries nerve impulses from the retina to the brain
- Blind spot : This area has no rods and cones ,therefore there is no vision at this point
- Vitreous humour: A jelly-like substance which gives shape of to the eye
- Lens: Changes shape for near and distant (far) vision
- Lris: The coloured part of the eye
- Aqueous humour: Watery fliud that supports the cornea and fronts chamber of the eye
- Pupil: A circular opening in the iris which allows light into the eye
- Suspensory ligament: Holds the lens in position
Accommodation
Is the adjustment of the shape lens to see clearly whether away or close by.
Distant vision (objects further than 6m)
- 1.Ciliary muscles relax
- 2.Suspensory ligaments tighten (become taut)
- 3.Tension ligaments tigten (become taut)
- 4.Lens is less convex (Flatter)
- 5.Light rays are refracted (bent)less
- 6.Light rays are focused onto the retina
Near vision (objects closer than 6)
- 1.Ciliary muscles contract
- 2.Suspensory ligments slacken
- 3.Tension on lens decreases
- 4.Lens becomes more convex (more rounded)
- 5.Light rays are refracted (bent) more
- 6.Light rays are focused onto the retina
Pupillary mechanism
The pupillary mechanism (or pupil reflex) regulates the amount of light entering the eye by adjusting the size of the
pupil
Light is briht
- 1.Radial muscles of the iris relax
- 2.Circular muscles of the iris contract
- 3.Pupil constsricts (gets smaller)
- 4.Less light enters the eye
Light is dim
- 1.Radial muscles of the iris contract
- 2.Circular muscles of the iris relax
- 3.Pupil widens (gets bigger)
- 4.More light enters the eye
Diseases and Disorders of the Eye
- Long-sightedness (Hypermetropia)
- Short-sightedness (Myopia)
Long-sightedness (Hypermetropia)
- Inability to see near objects less than 6 metres
How to correct
- Wearing glasses with convex lenses
Short-sightedness (Myopia)
- Inability to see distant objects less than 6 metres
How to correct
- Wearing flasses with concave lenses
Structure of the ear
Functions of the ear
-
Pinna:
Directs
sound
waves to
eardrum
-
auditory
canal: Transmits
sound waves to the
eardrum
-
Tympanum
(eardrum): Transmits
sound waves to the
middle ear
-
Ossicles:
Transmit
vibrations from
the eardrum to
inner ear
-
Eustachian
tube: Equalises
pressure on
either side of
the eardrum
-
Oval window:
Transmits sound
waves to the
inner ear
-
Round window:
Releases
pressure from
the inner ear
-
Semi circular canals:
Balance of the body
-
Sacculus and utriculus:
Balance of the body
-
Auditory nerve: Transmits
impulses to the brain
-
Cochlea: Contains the
organ of Corti which
converts sound waves
into nerve impulses
Hearing
- Sound waves are directed into the auditory canal by the
pinna.
- The sound waves make the tympanic membrane vibrate and
the vibrations are passed on to the ossicles in the middle
ear.
- The ossicles make the oval window vibrate and this causes
pressure waves to be set up in the inner ear.
- These vibrations also cause the organ of Corti to be
stimulated and it generates impulses which are sent to the
cerebrum along the auditory nerve.
- The cerebrum interprets the impulses as sound.
Balance
- Random changes in the speed and direction causes the endolymph inside the semicircular canals to move.
- This also causes fluids inside the semicircular canals to move.
- The movement of the fluids stimulates the receptors called cristae within the ampullae
- When the direction of head changes, gravitational pull stimulates different receptors called maculae, within the sacculus and utriculus
- The cristae and maculae (stimuli) are converted to nerve impulses
- These impulses are transmitted by the vestibular branch of the auditory nerve to the cerebellum
- The cerebellum sends impulses to the muscles to restore the balance
Diseases and Disorders of the Ear
- Middle ear infection
- Deafness
Middle Ear Infection
Is caused by bacteria
Treatment
- Insert grommets
- Antibiotics
Deafness
Is caused by damages to certain parts of the ear
Treatment
- Hearing Aid
- Cochlear implants
Endocrine system
What is an Endocrine System ?
Our bodies consist of two kind of glands:
- Endocrine glands
- Exocrine glands
Exocrine glands
Consist of ducts, e.g sweat ducts which carry secretions to the surface of the skin
Endocrine glands
Produces secretions that have to be transported for use far away from the gland itself e.g (Pituitary gland or hypophysis).
Hormones
Hormones are organic chemical messengers.
The human endocrine system
- The endocrine system is responsible for chemical coordination and regulates
activities that take place inside the body.
- The endocrine system consists
of glands that produce different hormones, which are the body's chemical
messengers.
Hypothalamus
ADH (antidiuretic hormone)
- Target organ: Kidney
- Controls the concentration of
water in the blood
Thyroid gland
Thyroxin
- Controls basic metabolic rate
Adrenal gland
Adrenalin
Increases:
- heartbeat
- blood pressure
- conversion from glycogen to
glucose
- blood supply to the cardiac
and skeletal muscles
- skeletal muscle tone
- rate and depth of breathing
- diameter of pupils
Decreases:
- blood flow to the digestive
system and skin
Aldosterone
- Target organ: Kidney
- Regulates salt concentration
in the blood
Ovary (only females)
Oestrogen
- Prepares the wall of the uterus by making it
- Thicker, vascular and full of blood
Progesterone
- Maintaince pregnancy
Testes (only males)
Testosterone
- Development of male secondary sexual characteristics
- Stimulates the maturation of sperm cells
Pancreas: Islets of Langerhans
Glucagon
- Stimulates conversion
of glycogen to glucose
(increases blood glucose
levels)
Insulin
- Stimulates conversion of
glucose to glycogen (reduce
Pituitary gland (hypophysis):
GH (growth hormone)
- Controls growth
TSH (thyroid stimulating
hormone)
- Stimulates thyroid gland to
secrete thyroxin
Prolactin
- Stimulates the production of milk by the mother
FSH
- Causes a follice in the ovary to become a Graffian follice
LH
- Converts raputured Graffian follice to corpus luteum
Negative feedback mechanisms
Operate in the human body to detect
changes or imbalances in the internal environment and to restore the
balance.
In other words if theres any changes in the body that are above normal the body release certain hormone to ensure that the body goes back to its normal form
How the negative feedback mechanisms works ?
- Step 1: An change is detected.
- Step 2: A control centre is stimulated.
- Step 3: Control centre responds
- Step 4: Message sent to target organ/s
- Step 5: The target organ responds.
- Step 6: It opposes/reverses the imbalance.
- Step 7: Balance is restored
Example : Thyroxin Level increase above normal
- Step 1: When thyroxin level increase above normal.
- Step 2: Pituitary gland is stimulated.
- Step 3: Pituitary gland produces less TSH.
- Step 4: TSH stimulates the thyroid gland.
- Step 5: Thyroid secretes less thyroxin.
- Step 6: Thyroxin level therefore decreases.
- Step 7: Thyroxin level goes back to normal
Example : Thyroxin Level decrease above normal
- Step 1: When thyroxin level decrease above normal.
- Step 2: Pituitary gland is stimulated.
- Step 3: Pituitary gland produces more TSH.
- Step 4: TSH stimulates the thyroid gland.
- Step 5: Thyroid secretes more thyroxin.
- Step 6: Thyroxin level therefore increases.
- Step 7: Thyroxin level goes back to normal
We will look at other examples when we do homeostatsis
Diabetes
Diabetes is caused when the body can no longer produce insulin therefore the glucose level of the blood rises.
There are two types of Diabetes
Type 1 diabetes
Occurs when the pancrease stops producing insulin.
Type 2 diabetes
Occurs when the insulin produced isn't enough or not functioning properly.
Symptoms
- Extreme thirts
- bured vision
- Weight loss
- non-healing of wounds
Treatment
- Excerise
- Eating healthy
Homeostasis in humans
What is Homeostatsis ?
This enables the body to function efficiently ,despite changes in the external or internal environment
Negative feedback mechanisms
- The level of glucose ,carban dioxide ,water and salt levels amongst others need to be kept constant,
within narrow limits, this means that the negative feedback mechanisms must work constantly also.
Maintaining the blood/sugar glucoso level
Increases
- Step 1: When glucose Level increase above normal.
- Step 2: Islets of Langerhans secretes Insulin.
- Step 3: Insulin decreases the glucose level.
- Step 4:Glucose Level than goes back to normal.
Decrease
- Step 1: When glucose Level decrease above normal.
- Step 2: Islets of Langerhans secretes Glucagon.
- Step 3: Glucagon increases the glucose level.
- Step 4:Glucose Level than goes back to normal.
Maintaining Oxygen and Carbon Dioxide Levels
Increases
- Step 1: When Carbon Dioxide Level increase above normal.
- Step 2: Medulla oblongata increases heartbeat and breathing rate.
- Step 3: Carbon Dioxide is expelled for the body and more Oxygen is taken up the lungs and sent to the cells.
- Step 4: Carbon Dioxide Level in the body decreases.
Maintaining water levels (Osmoregulation)
When the body has too much water
- Step 1: When water Level increase above normal.
- Step 2: The Pituitary gland secretes less ADH.
- Step 3: Less water is then re-absored so more water is lost in urine.
- Step 4: Water Level in then body decreases and goes to normal.
When the body has too little water
- Step 1: When water Level decrease above normal.
- Step 2: The Pituitary gland secretes more ADH.
- Step 3: More water is then re-absored so less water is lost in urine.
- Step 4: Water Level in then body increases and goes to normal.
Maintaining salt/soduim levels
When the body has too much salt
- Step 1: When sodium Level increase above normal.
- Step 2: The Adrenal gland secretes less aldosterone.
- Step 3: Less sodium is re-absored so more sodium is lost in urine.
- Step 4: Sodium Level in then body decreases and goes back to normal.
When the body has too little salt
- Step 1: When sodium Leveldecrease above normal.
- Step 2: The Adrenal gland secretes more aldosterone.
- Step 3: More sodium is re-absored so less sodium is lost in urine.
- Step 4:Sodium Level in then body increases and goes back to normal.
The process of temperature regulation
- Hypothermia: occurs when the body temperture drops below 37*C for an extended time .
it is caused by exetended exposure to cold conditions .More heat is lost than the body is able to produce.
- Hyperthemia: occurs when the body temperture increases above 37*C for an exetended time .
it is caused by prolonged exposure to high temperatures. The body produces and absorbs more heat then
it can lose.
Temperature regulation is the control of body temperature to keep it as
close to 370C as possible to enable the body to function normally
Body temperature is regulated by the hypothalamus in the brain and the
blood vessels and sweat glands in the skin.
On a hot day
- Step 1: Heat receptors in the skin are stimulated.
- Step 2: The stimulus is converted into an impulse and transmitted to the hypothalamus.
- Step 3: High blood temperature also stimulates the hypothalamus directly.
- Step 4: Nerves impluse are sent from the hypothalamus to the muscles of the blood vessels of the skin .
- Step 5: The blood vessels to the skin dilate ( this is called vasodilation).
- Step 6: More blood is sent to the surface of the skin and more heat is lost from the body.
- Step 7: More sweat is producted and more heat is lost by evaporation of sweat.
- Step 8: The temperature of the body drops back to normal body temperature.
On a cold day
- Step 1: Cold receptors in the skin are stimulated
- Step 2: The stimulus is converted into an impulse and transmitted to the hypothalamus.
- Step 3: low blood temperature aslo stimulates the hypothalamus directly.
- Step 4: Nerve impulses are sent from the hypothalamus to the muscles of the blood vessels of the skin.
- Step 5: The blood vessels to the skin constrict ( this is called vasoconstrition)
- Step 6: Less blood is sent to the surface of the skin and hence less heat is lost from the body
- Step 7: Less blood is also sent to the sweat glands
- Step 8: Less sweat is formed and less heat is lost by the evaporation of sweat
- Step 9: The temperature of the body rises back to the normal body temperature of the body rises back to
the normal body temperature.
Structure of the Skin
Plant Responses
Plant Growth Substances
A hormone is an organic substance produced in small amounts in one part of the body and transported to other parts where it controls the growth and development in some specific way.
Auxins, gibberellins and abscisic acid are some examples of plants growth substances that may be considered to be horomones
The Three types of plant Hormones
- Auxins
- Gibberellins
- Abscisic Acid
Auxins
- Brings about a bending reaction in plants known as tropism.
- Promote cell division
- Responsible for cell enlargement
- Promote root development
- Responsible for plant growth
Gibberellins
- Brings about elongation of the internodes of stems.
- stimulates root growth
- Promote development of flowers
- Helps in the germination of seeds
- Increases fruits size.
Abscisic Acid
- Brings about dormancy of seeds by slowing down germination, and dormancy of apical buds.
- Induces flowering in some plants
- Helps in the closing of stomata during periods of water shortage or drought
- Promotes the ageing of Leaves
Phototropism and Geotropism
A tropism is a growth movement or bending reaction of a plant (or part of a plant) in response to an external stimulus.
- The direction of growth or bending of the plant depends on the direction of the stimulus.
- When the external stimulus is light, this is known as phototropism.
- If the external stimulus is gravity, this is known as geotropism.
Phototropism
Is the growth movement of plant organs in response to the stimulus of light.
- Stems are positively phototropic i.e they growth towards light.
- Roots are negatively phototropic i.e they grow away from light.
Geotropism
Is the growth movement of plant organs in response to the stimulus of gravity.
- Roots are positively geotropic while stems are negatively geoptropic.
Role of auxins in Phototropism
- Auxins are produced at the tip of the stem from where they move downwards evently.
- The even distribution of auxins brings about equal growth on all sides of the stem.
- Therefore, the stem grows straight upwards.
- When stems are exposed to unilateral light(light from one side) the brightly-lit side
suffers from a shortage of auxins probably because the auxins are destroyed by the light or because
they move to the darker side.
- A high concentration of auxins in stems promotes growth.
- Thus an uneven distribution of auxins causes uneven growth of the stem with the darker side growing faster
- The stem thus bends towards the light i.e stems are positively phototropic.
Role of auxins in Geotropism
- Auxins are produced at the tip of the root from where they move upwards evently.
- The even distribution of auxins brings about equal growth on all sides of the root.
- Therefore, the stem grows straight downwards.
- When a root is placed horizontally the auxins accumulate on the lower side probably because of gravity.
- A high concentration of auxins in roots inhibits growth.
- Thus an uneven distribution of auxins causes uneven growth of the root with the upper side growing faster.
- The root thus bends downwards i.e roots are positively geotropic.
Weed Control by using Growth Hormones
- Hormone weed-killers are auxin-based selective herbicides, which are pesticides that kill only one specific unwanted plant as
they are used in the appropriate dosage.
- Hormone weed-killer is made by chemical synthesis and are the main factor in controlling weed growth.
Advantages of Hormone weed-killers
- Non-Toxic to Animals or Humans.
- Eliminate the need to hand pick annoying unwanted weeds in the garden.
Disadvantages of Hormone weed-killers
- May damage other plants if over used.
- Can affect plant growth.
Plant Defence Mechanism
This deals with how the plant protects itself from being eaten by other animals/inserts.
Plants protect themselves using chemicals and thorns
Thorns
- Some plants have thorns on their stems and leaves.
- These thorns serve as protection and keep herbivoures at bay
Chemicals
- Plants that use chemical defense secrete poisonous chemicals that may kill many organisms.
- Many organisms avoid theres plants.
Natural Selection
Hypothesis and Theory
In science a Theory is an idea that has been well tested and shown to be widely applicable, preferably one that
has not been falsified by a better 'theory'.
And
In science a Hypothesis is an untestable idea that cannot be falsified at the time, but would explain a great deal of great
importance if true.
What is Evolution ?
The theory of evolution states that all the things we see today arose from things that existed in the past but they look
different because things change over long periods of time.
Biological evolution is a special type of evolution that refers to changes that living things have undergone over long periods of time.
Simple english
- The theory of evolution states that everything we see today living, came from things that have lived before , along time ago, but now they look different from them because thing change over long periods of times.
Variation within a species
Species
- refers to a group of similar organisms that are able to interbreed to produce offsprings , that will be able to interbreed.
Population
- refers to organisms of the same species living in the same area at the same time, and can interbreed.
Variation
- refers to the small differences that exist between individuals of a species or population (e.g) differences in height, differences in
eye colour etc..
Sources of variation
Things that bring about change amongst species(organisms).
1) Mutation
- Mutations involves a change on the structure of a gene.
2) Meiosis
Crossing-over
- During Prophase 1 chromosome exchange genetic material bring about variation.
Random arrangement of chromosome
- During Metaphase 1 and Metaphase 2 Chromosomes/chromatids align themselves in equator at random positions bring about variation
3) Random fertilisation of gametes
- Every egg cells and sperm cells produced during meiosis are different form each other. Since there is random
fertilisation of these gametes, there will be different combinations of genetic material in the offspring.
Continuous and Discontinuous Variation
Continous variation
In continous variation, variation is endless there is a range of different phenotypes for a particular characteristic. Example
lets look at the height of a human , we can see that there is a complete range of measurements.
Discontinuous variation
In discontinous variation, there is no range of different phenotype its (either this or this) for a particular characteristic. Example Human blood Group it either A, B ,O or AB
Evidence for Evolution
Previously you learnt that according to the theory of biological evolution, all organisms we see today came from organisms that existed in the
past but they look different today because things change over time.
For scientists to determine if two species are closely related to each other or have a common ancestor, they must study the characteristics of the species
concerned.
Scientist provide us with evidence to support the theory of evolution.
Evidence of the theory of evolution
- Paleontology
- Comparative anatomy
- Comparative embryology
- Biogeography
- Molecular biology and genetics
Evidence from Paleontology
Paleontology : is the study of fossils
- Fossils are the remains of ancient life forms preserved in the rocks, e.g bone fragments etc..
How do scientists tell the age of a fossils ?
"There Two ways scientists can tell the age of fossils"
Using Relative dating and radiometric dating
- Relative dating: In relative dating scientists try and figure out the age of a fossil by comparing the age of another fossil or geographical event, such as volcanic eruption.
- Radiometric dating: In radiometric scientists attempt to find out the age of a fossil by finfing out how long ago a particular fossil was formed.
Fossils provide the only direct evidence of the history of evolution
Evidence from Comparative Anatomy/Modification by descent
Scientists used comparative anatomy to determine relationships between species
Organisms with similar structure, they argue, must have acquired these traits from a common ancestor
For example lets look at the forelimp structure of certain vertebrates like (mole, bat, horse, seal, monkey) they all have a basic struture
plan suggesting that they may arose from a common ancestor
Homologous struture
- The structure which have the same basic plan, but have different functions e.g Human forelimp and cat forelimop
Analogous struture
- The structure peforms the same function but is different from other strutures e.g butterfly and bird
Evidence from Biogeography
Biogeography is the study of the distribution of life forms over geographical areas.
Other evidence in support of evolution comes from biogeography, this is what first suggested to charles darwin that species evolve from a common ancestor.
Evidence from Molecular Biology and Genetics
Scientists argue that organisms are closely related if they have...
- Identical DNA Struture
- Similar Sequence of Genes
- Similar Portions of DNA with No Function
- Identical Protein Synthesis and Similar Protein
- Similar Respiratory Pathways
Evidence from Comparative Embryology
By comparing the structure of an embryo in its early development stage , scientists figured that most vertebrates embryo look alike in their early development stage this could be because they arose from a common ancestor.
For Example the embryo, of a fish , chicken, pig and human all look alike and sometimes are even hard to differeniate.
Lamarckism
Lamarckism is the idea that organisms can pass on their characteristics, that they have acquired during their lifetime to thier offsprings.
It was named after the biologist Jean-Baptiste de Lamarck (1744-1829).
Jean-Baptiste Lamarck explained evolution (On how organisms undergone change) using the following two ‘laws’.
1) The law of inheritance of modified/acquired characteristics:
- For this Law Lamarck believes that change in organisms happpened because they deliberately wanted to change to better adopte to the enviroment.
Example : The long neck of the giraffe came about because it wanted to feed on the tree tops, to avoid competition.
2) Law of use and disuse:
- For this Law Lamarck believes that when an organisms uses a structure or an organ more regular, it becomes better developed or enlarged overtime.
If an organisms does not use a structure or organ frequently, it becomes less developed or reduced in size and may disappear altogther.
Why Lamarck's theory is rejected by most biologists
- Biologists say that Organisms evolved, not because they wanted too, but because change took place randomly in response to the enviroment
- Biologists say that there just not enough evidence to prove/support Lamarck's idea that changes brought about by adoptation to the environment are inherited from parent to offspring
Darwinism
Darwinism is a theory that explains the evolution of new species through natural selection.
It was named after Charles Darwin (1809-1882)
Charles Darwin theory of evolution is based on 5 main observations and assumptions
- Variation:There is a great deal of variation among members of the same
species.
- Offspring:Species produce a large number of offspring but not all survive.
- Competition:Organisms compete for limited resource, such as food and teritory.
- Genetics:Organisms pass genetic traits on to their offspring.
- Natural Selection:Those organisms with the most favourable characteristics are more likely to survive and reproduce.
Darwin's Theory of Evolution by Natural Selection
- Both plant and animals generally produce a large number of offspring.
- The offsprings produced of the same species show a great deal of variation.
- The offsprings produced compete with each other for avaliable resources.
- Only those with favourable characteristics will survive and reproduce.
- Darwinism called this Natural selection
- Since the individuals with favourable characteristics survive, they will continue to reproduce offsprings that are
have favourable characteristics.
- Organisms which do not have favourable characteristics, will not cope with the environment and therefore die.
Difference between Lamarck's and Darwin's Theories
Lamarck's Theory
- Variation in offspring brought by individuals in the population changing
- Change is brought about because individuals in the population wanted to change
- Change brought about by individuals in the population adapting to the environmnet
- Individuals in the population change
- Changes brought about by adaptation to the environmnet are inherited from parent to offspring
Darwin's Theory
- Offspring showed variation from the moment of their production
- Change as a result of environmental factors working randomly on the population
- Change brought by nature selecting those that are best suited to environmnet to survive
- The population as a whole changes
- Characteristics are passed on from generation to generation because they enable the inidividuals to survive in the environment.
Punctuated Equilibrium
According to this theory, most species do not undergo any change for long period of time. Then, suddenly, the species undergo rapid change over
a short period of geological time, resulting in new species.
Theory of punctuated equilibrium for the tiger stripes
- Millions of years ago, there were lot of tigers without black strips.
- Then suddently, a mutation occurred in a few of the animals, causing some of the tigers to be born with stripes
- Tigers with stripes were able to camouflage themselves from prey using tall grasses and trees.
- Tigers without stripes were out-competed by tigers with stripes.
- Over only a few generations, the whole population was born striped.
Gradualism
- Gradualism is selection and variation that happens more gradually.
Theory of gradualism appiled for the stripes of tigers
- At first, the entire population of tigers was without stripes.
- Some tigers developed marks on their fur, as a result of mutation.
- Marked tigers were able to camouflage themselves better than the stripes less tigers, so few tigers without stripes survived.
- At the same time, the marks gradually became clear stripes.
- Eventually, the entire population of tigers became striped.
Artificial Selection
Artificial selection is a form of selection which humans actively choose which traits should be passed onto offsprings to have desirable characteristics.
Differences Between Artificial Selection and Natural Selection
Definition
- Natural Selection: Natural selection is the process whereby organisms better adapted to their environment tend to survive and produce more offspring.
- Artificial Selection: Artificial selection refers to the process by which animals and plants are chosen by the breeder to produce desirable and inheritable characters in the successive generations.
Selection
- Natural Selection: Natural selection is a nature-made selection process.
- Artificial Selection: Artificial selection is a man-made selection process.
Significance
- Natural Selection: Natural selection produces a huge biological diversity.
- Artificial Selection: Artificial selection produces organisms with selected traits.
Occurs in
- Natural Selection: Natural selection occurs in natural populations.
- Artificial Selection: Artificial selection mainly occurs in domestic populations.
Importance
- Natural Selection: Natural selection only allows favorable characters to be inherited over the successive generations.
- Artificial Selection: Artificial selection allows only selected traits to be inherited over successive generations.
Speed
- Natural Selection: Natural selection is a slow process.
- Artificial Selection: Artificial selection is a rapid process.
Effect on Evolution
- Natural Selection: Natural selection facilitates evolution through generating biological diversity.
- Artificial Selection: Artificial selection does not facilitate evolution.
Speciation
Speciation : means the formation of new species.
Types of Speciation
- Allopatric speciation
- Sympatric speciation
Allopatric speciation
- New species are formed who a population of the same species becomes separated by a geographical barrier e.g contient split, mountain or river.
- Each sub-population then develops into a new species.
Sympatric speciation
- New species are formed without the presence of a geographic barrier to separate the population.
- Instead the population may develop reproductive barrier which prevents them from interbreeding, resulting in separate species.
Speciation by Geographic isolation (Allopatric Speciation)
- A population of a particular
species may become split...
- by a geographical barrier, e.g.
a river.
- As a result, the two parts of the population cannot interbreed
- There is no gene flow between the two populations.
- Natural selection occurs independently in each population.
- This is due to different environmental conditions.
- As a result, the two populations become genotypically and
phenotypically different over a period of time.
- Even if the two populations mixed at a later time, they will not be
able to interbreed again.
- We say that one or both parts of the population have become a new
species = speciation.
Mechanisms of Reproductive Isolation
Reproductive isolation or reproductive isolating barrier are factors that prevent two species from producing fertile offspring.
Habitat Isolation
- When two closely related species live in different habitats.
Temporal Isolation
- When two species breed during different times (seasons) of the year.
Species-specific Courtship Behaviour
- When two species develop develop new ways of attracting mates that might not attract the other mates.
Adaptation to Different Pollinating Agents
- Differences in structure can prevent successful mating.
Prevention of Fertilisation
- In some closely-related species fertilization of the different species is prevented by the different species having different copulatory organs.
Hybrid Infertility
- Some closely-related species may mate and produce viable offspring.
Evolution in Present Time
Scientists have used the way in which insects have developed resistance to insecticides, and the way in which bacteria have developed resistance to antibiotics as examples of evolution by natural selection in present times.
The developement of Resistance to insecticides by insects
- There is great deal of variation amongst mosquitoes.
- Insecticides were created to kill mosquitoes.
- Some mosquitoes became resistent to the insecticides.
- More mosquites resistent to the insecticides lived and reproduced and produced fertile offsprings that are also resistance.
- While those without resistance died.
- Thats how the population of resistent mosquites evolved.
Human evloution
Our Place in the Animal Kingdom
There are Five kingdoms one of which is the Kingdom Animalia or commonly called the Animal Kingdom
Animalia/Animal Kingdom
There two large groups within the Animal kingdom
- Invertebrates (Animals without bones)
- Vertebrates (Animals with bones)
Vertebrates
Vertebrates can be sub-divided into the following classes
- Class Pisces (fishes)
- Class Amphibia (frogs)
- Class Aves (birds)
- Class Reptilia (snakes and lizards)
- Class Mammalia (rabbits, monkeys, humans) *
Modern Humans are classified as Primates.
The scientific name for Modern Human is Homo sapiens.
Early Humans are often called ape men, since they showed some characteristics of apes and some characteristics of humans.
Order Primates
There two sub-orders that exist with the Order Primates
- Anthropoidea (Monkeys, apes and humans).
- Prosimii
Anthropoidea
Three families exits with the Anthropoidea
- Hylobatidae : Gibbons
- Pongidae : orangutans, gorillas and chimpanzees
- Hominidae : Humans
Hominid and Hominin
Note : The family pongidae doesn't exist anymore since scientist believe that African Apes are closely related to Humans.
- Now the African Aps fall under the Hominidae family.
Hominid: All modern and extinct great apes. Gorillas, chimps, orangs and humans and their immediate ancestors.
Homini:Any species of early human that is more closely related to humans than chimpanzees, including modern humans themselves.
Similarities betweeen African Apes and Humans
The Upper Limbs
- Opposable Thumbs
The Brain
- Large brain compares to their bidy masses
Vision
- Cones and rods
- Binocular vision
Number of offsprings produced
- Fewer offsprings than other mammals
Upright posture
- Ability to sit upright
African Apes
- Quadrupedal - knuckle-walkers
- Foramen magnum (opening for spinal cord) at back of skull
- C-shaped vertebral column
- Arms longer and stronger than legs
- Knee joints smaller and weaker
- Opposable (grasping) big toe with power grip
- Flat feet
- Long and narrow pelvis
- Smaller, less developed brain
- Large, prominent canines
- Thin tooth enamel
- Large, prominent jawbone with no chin (prognathism)
- Wider, sloping face
- Narrow, rectangular palate
- Prominent cranial and brow ridges
Humans
- Bipedal - walk upright on two legs
- Foramen magnum closer to front of skull (central under skull)
- S-shaped vertebral column
- Arms shorter and weaker than legs
- Knee joints larger and stronger
- Non-opposable (forward-thrusting) big toe in line with other toes
- Curved foot arch
- Short and wide pelvis
- Large, developed brain
- Smaller canines; the same size as other teeth
- Thick tooth enamel
- Rounded jaw with developed chin (reduced prognathism)
- Narrow, flat face
- Wider, more curved palate
- Reduced cranial and brow ridges
Evidence of common ancestors for living hominids (including humans)
- The evolutionary theory does not state that humans evolved from the chimpanzee or the gorilla, but it proposes that they share a common ancestor.
- Scientists are searching for a common ancestor of all living hominids.
- The big question scientists have to answer is whether the common ancestor was ape-like or human-like.
- Remains of earlier hominids are very rare.
Three main lines of evidence
- Fossil evidence
- Genetic evidence
- Cultural evidence
Fossil evidence
- Paleontologists study fossils to provide more information on the structure, movement, lifestyle and environment of a particular species.
- Certain features of hominid fossils indicate how changes occurred over time.
- Hominid fossils are rarely complete and consist mainly of fragments.
- Most hominid fossils are teeth, jaw bones or skull fragments.
- The remains of feet, hands, pelvic bones or vertebral columns are scarce.
- Long bones e.g. femurs are more commonly found.
- In the search for a common ancestor for hominids, palaeontologists look particularly at the following features of hominid fossils:
- bipedalism
- brain size
- dentition (teeth) prognathism
- palate shape
- cranial
- brow ridges
- Bip
Bipedalism
- The greatest observable difference between apes and humans lies in the difference in posture and method of locomotion.
- Apes are four-footed (quadrupedal) with gorillas and chimpanzees demonstrating a particular manner of walking, i.e. knuckle-walking.
- Humans, however, are bipedal and walk upright.
Advantages of bipedalism
Upright bodies expose a smaller surface area to the sun which reduces risk of overheating while hunting, foraging or escaping predators.
Upright bodies expose a larger surface area to air currents which causes cooling and reduces dependency on water.
Hands are free to use tools, prepare food, carry young, hunt or fight.
Vision extends further over the tall grass of the savannah to find food or avoid predators.
Adaptability to occupy a wider range of habitats.
The human vertebral column is S-shaped for flexibility and shock absorption. The vertebral column of apes is C-shaped.
Brain size
- Hominid fossils indicate that the size of the cranium increased in most fossils over time.
- We may conclude that, in general, the size of the brain (brain capacity) increased over time.
- The cranium of apes is small and elongated and contains a small, less developed brain.
- Chimpanzee brains have an average size of approximately 395 cm3.
- Humans have a more rounded skull with an enlarged cranium which contains a large, highly developed brain.
- The average size of the human brain is approximately 1 400 cm3.
- The more complex human brain gave rise to:
- well developed hand-eye coordination (to make and use tools)
- The capacity for language
- The use of fire
Dentition (teeth)
- The size of teeth decreased with the course of evolution.
- Apes have large prominent canines that are larger than other teeth.
- In apes, there is a large gap (diastema) between the incisors and the canines. It provides space for the protruding canines on the opposite jaw so that the mouth can close.
- The human canines are the same size as the other teeth.
- The diastema disappeared completely over time.
- The tooth enamel became thicker over time. In apes it is very thin, in hominins it is thicker and in humans it is very thick.
Prognathism
- Apes have large, protruding jaws (snout or muzzle) without a chin.
- Humans have a narrow, flat face with rounded jaws and a protruding chin.
Genetic evidence
Scientists states that organisms are closely related and likely to have a common recent ancestor if they have.
- Identical DNA structure
- Similar sequence of gene
- Similar portions of DNA with no function
Cultural evidence: tools
- The production and use of tools and other cultural practices like fire-making, burial rites, art and hunting techniques are suggested as further evidence of common ancestors for living hominids.
- The development of speech and language is another cultural change that distinguishes modern humans from primates.
Major phases in the hominid evolution (from 6 mya to present)
- The main hominin genera within the hominid group are the following:
- Ardipithecus
- Australopithecus
- Homo
- The timeline of human evolution probably began 6 - 7 million years ago.
Ardipithecus
- Ardipithecus ramidus was an early hominin that lived approximately 5,8 - 4,4 million years ago.
- About 17 Ardipithecus fossils were found in the Afar valley of Ethiopia in 1993.
- These beings show ape-like as well as australopithecine characteristics, indicating that Ardipithecus could be a transitional form between the apes and Australopithecus.
General characteristics of Ardipithecus
- Probably bipedal.
- Foramen magnum positioned centrally below skull, but more to the front than in apes.
- Pelvis is wider at the top, and narrow and long at the bottom as in apes.
- Long arms (almost as long as the legs) for climbing trees.
- Opposable, grasping big toe.
- Small brain capacity of approximately 300 - 350 cm3.
- Ape-like teeth, but smaller canines and molars; a diastema is present
- Protruding jaw (snout/muzzle) without a chin.
- Sloped face.
- Palate is narrow and rectangular.
- Small brow ridges.
Australopithecus
- Australopithecines are regarded as the first bipedal primates.
- They have both ape-like and human-like characteristics and they are sometimes called ape-men.
- The genus name Australopithecus literally means 'southern ape'.
- It is estimated that australopithecines lived in Africa between 4,5 and 1,4 million years ago.
- During this time the African forests increasingly made way for sparse woodlands, grasslands and savannas.
- Australopithecus fossils were found mainly in Eastern and Southern Africa.
General characteristics of Australopithecus
- Bipedalism and upright walking.
- Foramen magnum is positioned centrally below the skull. Pelvis is short and wide.
- Long arms for tree climbing.
- Fingers long and curved; non-opposable big toe.
- Brain capacity larger than that of the apes, approximately 380 - 500 cm3.
- Teeth more human-like; smaller canines than apes, but larger than humans; small diastema.
- Protruding jaw without a chin.
- Sloping face (less sloping than in apes).
- U-shaped palate.
- Large brow ridges.
- The 3,8 million year old footprints discovered in Laetoli,Tanzania are one of the oldest fossils indicating evidence of bipedalism of Australopithecus.
- Australopithecus probably developed simultaneously with the Homo genus and is therefore not regarded as a human ancestor.
- Various Australopithecus fossils of different species have already been found in Africa
Five well-known australopithecines
- Taung child
- Mrs Ples
- Lucy
- Little Foot
- Australopithecus sediba
Taung child (Australopithecus africanus)
In 1924 the fossil skull of a hominin was found by Professor Raymond Dart at Taung, northwest of Kimberley.
- It was the skull of a child of about 3 - 4 years old.
- The skull had human as well as ape-like characteristics: a small brain capacity (340 cm3) similar to apes human-like teeth foramen magnum in a more central position, indicating bipedalism
- The Taung skull is classified under Australopithecus africanus, who lived about 3 - 2 million years ago.
Mrs Ples (Australopithecus africanus)
In 1947 a complete adult skull and various bones were found by Dr Robert Broom in the Sterkfontein Caves in South Africa.
- This skull was about 2 - 3 million years old and was also classified as Australopithecus africanus.
- The brain capacity is estimated to be similar to that of a chimpanzee.
- From the position of the foramen magnum it could be deduced that Mrs Ples was bipedal and walked upright.
- The jaws indicated that there were no protruding canines, and the dentition indicated a diet of mainly plant material with little meat.
Lucy (Australopithecus afarensis)
Lucy is a fossilised female skeleton found by Donald Johanson at Hadar in the Afar valley, Ethiopia in 1974.
- The skeleton dates back 3,5 million years.
- The shape of the pelvis indicated that Lucy was female.
- The skeleton was about 1 m long and showed evidence of bipedalism.
- The face had ape-like characteristics, i.e. a low forehead, flat nose, protruding lower jaw and large canines.
- The arms were long and the legs short.
- The brain capacity of 400 cm3 was similar to that of apes.
Little Foot (Australopithecus species)
In 1994 the ankle and foot bones of an australopithecine fossil was discovered in the Sterkfontein Caves by the palaeoanthropologist Dr Ron Clarke.
- The fossil was named Little Foot.
- The rest of the skeleton was found in 1997.
- The excavation of the complete skeleton from the rock is still in progress.
- It has already been determined that Little Foot was bipedal because of the position of the foramen magnum.
- The arms are short and the bones of the hand are very similar to those of the modern human, with short palms and fingers.
- The species to which Little Foot belongs will only be determined when the entire skeleton has been removed.
Australopithecus sediba (2 - 1,7 mya)
- In 2008 two fossils, those of a young woman and boy, were discovered in the Cradle of Humankind in the Malapa area by Professor Lee Berger and his 9-year-old son, Matthew.
- These fossils represent a new species, Australopithecus sediba, which was announced to the world in April 2010.
- The fossils are between 1,78 and 1,95 million years old and the most complete early hominins discovered so far.
- Australopithecus sediba is considered a transitional fossil between the older Australopithecus africanus and the first Homo species, and possibly gave rise to the origin of modern humans.
- Australopithecus sediba has a small brain and large brow ridges in comparison to modern humans, but the shape indicates a more advanced brain than that of other australopithecines.
- Early australopithecines were able to walk upright, but could not run fast or walk for long distances.
- Similarly, Australopithecus sediba had long arms and short hands adapted for tree climbing, while the pelvis was similar to that of early Homo species and adapted for walking long distances.
- Professor Berger and his colleagues believe that Australopithecus sediba could probably be the ancestor of modern humans.
HOMO
- The genus Homo appeared in Africa about 2,2 million years ago.
General characteristics of Homo
- Bipedalism with upright walking.
- Central foramen magnum at the base of the skull, directly above the vertebral column.
- Pelvis is short and wide.
- Legs are long in relation to arms; longer femurs for greater stride.
- Short, straight toes; non-opposable big toe; enlarged heel bone; opposable thumb.
- Larger brain with a brain capacity of approximately 600 - 1 400 cm3.
- Smaller teeth (no protruding canines), no diastema.
- Jaws more rounded with a prominent chin in Homo sapiens; older species have protruding jaws.
- Flat face.
- Wide, curved palate.
- No brow ridges in Homo sapiens; older species have large brow ridges.
Homo species
- Homo habilis
- Homo erectus
- Homo neanderthalensis
- Homo sapiens
Homo habilis (handy man)
Homo habilis lived in Africa, together with other Australopithecus species, about 2,2 - 1,6 million years ago.
- Australopithecus africanus probably gave rise to Homo habilis.
- In 1960 a Homo habilis fossil was discovered in Tanzania.
- The body of Homo habilis was smaller than that of Australopithecus and it was ape-like.
- They also had a larger brain (640 cm3) than Australopithecus, which meant they had better skills in using their hands to make tools.
- Homo habilis was the first group that used stone tools.
Homo erectus
- Homo erectus is a species that is closer to modern humans than to Australopithecus.
- Homo erectus literally means 'upright man' and they lived 1,8 - 0,3 million years ago.
- They were probably the first hominins to migrate from Africa to Europe and Asia.
- The most complete Homo erectus fossil is 1,5 million years old and was found Differences between genera Australopithecus and Homo near Lake Turkana in Kenya. It is known as the Turkana boy.
- Homo erectus had large bodies, similar to those of modern humans.
- Their skulls were thick with low, prominent foreheads, heavy brow ridges and no chin.
- Both jaws were relatively massive with large teeth.
- Their brain capacity was about 1 000 cm3.
- Homo erectus made and used stone and bone tools.
- They were successful hunters and the first species that learnt to use fire
Homo neanderthalens
- The Neanderthals were a group of people that lived between approximately 230 000 and 30 000 years ago in Europe and Western Asia.
- The first fossil was discovered in 1856 in the Neander Valley in Germany.
- Their skulls were long and flat, with a low forehead, broad nose and a prominent brow ridge above the eyes.
- Although their brains were larger than Homo sapiens, language was not well developed and their technological development was limited.
- They were hunters, wore clothes made from animal skins, built shelters in caves and used fire.
- They buried their dead, which is an indication of some form of 'spiritual life' or advanced culture.
Homo sapiens
- This group is considered to be the direct ancestors of modern humans.
- Presumably, Homo sapiens appeared about 200 000 years ago.
- It is claimed that the appearance of Homo sapiens resulted in the disappearance of the Neanderthals.
- Homo sapiens developed better skills and had more advanced technology.
Therefore modern humans are not directly related to Homo neanderthalensis.
- Homo sapiens used tools made from bone as well as stone, which included spears, arrows, bows and hooks for fishing.
- Their clothes were made mainly from leather and plant material.
- They lived in tents and formed communities.
- As hunters they followed the annual animal migrations in the summer.
- They developed agriculture and cultivated the land.
- They wore jewellery and decorated their bodies with paint.
- They developed rituals that were linked to hunting, births and deaths
- Like the Neanderthals, they buried their dead which indicates a development of advanced culture and spiritual rituals.
'OUT OF AFRICA' Hypothesis
- According to the 'Out of Africa' hypothesis, Homo sapiens originated in Africa about 200 000 years ago and migrated relatively recently (50 000 ya) to the rest of the world.
- These early Homo sapiens had a higher level of technological skills, were better adapted to their new environment and out-competed other Homo species.
- This resulted in the more successful Homo sapiens replacing Homo erectus in Asia and Indonesia and Homo neanderthalensis in Europe.
Evidence of african origins for all modern humans
The following evidences support this hypothesis:
- Genetic links
- Fossils and artefacts of hominins found in Africa
Genetic links as evidence for the ‘Out of Africa’ hypothesis
- Scientists increasingly make use of genetic studies where sections of DNA are used to determine ancestry.
Different types of types of DNA are used:
- Chromosomal DNA (excluding Y-chromosomes)
- Mitochondrial DNA (mtDNA)
- Y-chromosome DNA
Arguments against Evolution
People who do not believe in evolution put forward four main arguments aginst evolution. They say that:
- The Earth is only about 6 000 years old not 4.5 billion years old as claimed by those who believe in evolution.
- The probability of forming a single molecule by chance is incredibly small.
- When things are left on their own, they get more disorderly or less organized.
- The fossil record has too many gaps in it to be accepted as proof of evolution
Some Alternate Theories of Diversity
Creationism
- The believe that all living forms have been created by some Supreme Being.
So the organism that have been created have not changed since their creation.
- Different forms of life were designed to functionin particular settings.
Intelligent Design
Theory is based on the following ideas:
- Cells are too highly organised to have arisen on their own.
- The differences between different kinds of organisms are too complex for them to have evolved from a common ancestor
Literalism
- Taking whats writtern in religious books to be literally true.
Theistic Evolution
- Theistic evolutionists believe in God and Evolution, they say that natural selection is simply the plans of gods.
Human Impact
The atmosphere and climate change
- Climate refers to the long-term weather conditions of an area.
- The atmosphere is made up of nitrogen, oxygen and other gases, which include the greenhouse gases such as carbon dioxide and methane.
- The greenhouse effect is important in keeping the Earth warm so that it can sustain life. However, an increase in the concentration of greenhouse gases leads to the ‘enhanced greenhouse effect’.
As a result, there may be a significant rise in the average temperature of the surface of the Earth over a period of time. This is known as ‘global warming’
Increased concentration of carbon dioxide in the atmosphere is due mainly to:
- Burning of fossil fuels (for electricity, to power vehicles and for industrial processes): Combustion of carbon-rich fuels such as coal or plants (w ood) releases carbon that was stored in them, as carbon dioxide.
- Deforestation : Cutting down trees and removing vegetation from the land decreases the amount of carbon dioxide taken up by plants during photosynthesis. This increases the amount of carbon dioxide available in the atmosphere.
Increased concentration of the methane in the atmosphere is due mainly to:
- The increased number of landfills: decaying organic matter in waterlogged soils such as landfills releases methane.
- The increased number of livestock: ruminants such as cows release methane gas through their digestive tracts.
- Mining of coal.
Increased temperatures may lead to:
- More evaporation of water which can lead to increased precipitation which eventually increases the potential for flooding.
- Rising sea levels caused by melting ice in the glaciers which can eventually increase the potential for flooding.
- Increased wildfires that increase the chances of soil erosion and eventually desertification.
- Increased loss of biodiversity, as species are unable to cope with rapidly rising temperatures, eventually leading to desertification.
- Increased droughts in some areas leading to desertification and food insecurity.
Carbon footprint
This is a measure of the total amount of carbon dioxide emissions of an individual, a defined population or a company per year.
Strategies to reduce the carbon footprint include the following:
- Reuse and recycle: less fossil fuels burnt in the production of some of the material.
- Drive less: by using public transport, walking, bicycles.
- Reduce the need for heating: insulating walls and building energy efficient homes.
- Carbon offsetting: by using alternative energy (solar and wind) and reforestation to act as a carbon reservoir.
- Technological developments: decrease the amount of energy needed for production/decreasing the dependency on carbon emitting fuels.
Destruction of the ozone layer
Ozone is a greenhouse gas that is found at low concentrations 15 – 50 km above the Earth’s surface.
If the measures to reduce the destruction of ozone layer fail:
- There will be a significant increase in the number of skin cancer cases.
- Ultraviolet rays reaching the Earth’s surface may cause permanent damage to our eyes.
Availability of water
The availability of water may be influenced by the following factors:
Construction of Dams
- The construction of additional dams plays a major role in increasing the quantity of water stored and made available for later use by people and in agriculture.
Destruction of wetlands
- Wetlands should not be destroyed because they influence both the availability and quality of water.
Water wastage
- A large amount of water used for irrigation is lost due to poor farming practices. Open drain irrigation leads to loss of water by evaporation. The use of water for irrigation further up a river decreases the availability of water for other users lower down the river.
- Availability is also affected by wastage of water through leaking taps and toilets and faulty pipelines.
- Wastage of water can be reduced by reducing the pressure in the pipes, by educating people to use water wisely and by maintaining all plumbing in good condition.
Cost of water
- The cost of water is influenced by costs involved in increasing the availability and quality of water.
- The cost per kilolitre (kl) of water increases with the increased use of water. This is meant to discourage over-use of water, thus allowing for its sustained use.
- A certain amount of water is available free to all citizens to ensure that water is available to the poorest.
Poor farming practices
- Contamination of water sources by fertilizers and pesticides has decreased the amount of clean water available, thus increasing the costs involved in purification.
- Over-grazing leads to soil erosion. On land that is eroded, water runs off rapidly rather than soaking into the ground, and is thus wasted.
Droughts and floods
- During periods of drought, water availability decreases. Water used from dams during the drought periods cannot be easily replaced.
- Natural vegetation can hold back water from floods. If the natural vegetation is removed, flood waters are lost.
Boreholes and their effect on aquifers
- Boreholes have been used to increase water availability in areas that do not have direct access to other sources of water.
- Constant use of boreholes eventually leads to the drying up of aquifers (the source of borehole water) thus decreasing water availability in the future.
Water recycling
- The availability of water can be increased if existing water is used for more than one purpose. For example, some water used in the household can be used for the garden. Sewage water can be treated and used again.
Exotic plantations and the depletion of the water table
- Some exotic plants use a large quantity of water from the ground. As a result, this decreases the level of the water table, making less water available to other vegetation in the area.
Quality of water
The quality of water may be influenced by the following factors:
Eutrophication and algal bloom
- Water used for agriculture may contain pesticides, herbicides and fertilizers which pollute the water in rivers, dams and lakes, causing eutrophication. The added nutrients lead to an increase in algal growth (algal bloom). These algae over-use and thus deplete the oxygen in the water, thus reducing the potential for life in such water.
Thermal pollution
- Thermal pollution refers to the heating of water caused by the use of water for cooling in power-stations and industries.
- The quality of water is affected because heated water has a lower oxygen content, making it difficult to support life.
Pollution of water through domestic, agricultural and industrial use
- After water is used for domestic purposes it may contain detergents (such as from washing) and pathogenic bacteria (such as in sewage). This polluted water has to be treated before it can be used again.
- After water is used for industrial purposes it may contain many heavy metals, oil, heat and fertilizers. This adversely affects the quality of the water and all life that depends on it.
- Fertilisers and pesticides may run off into rivers, ponds and dams and pollute the water.
Mining
- Water returned to the environment from mines is generally acidic and toxic. This water is hot and thus also contributes to thermal pollution.
Alien Plants
- Alien invasive water plants block the waterways, reducing light to other aquatic plants. These plants eventually die and decompose. Bacteria that decompose these plants eventually deplete the oxygen supply in the water.
Water purification
- The quality of water is improved through purification methods. Undrinkable water can be made drinkable.
Food security
Food security refers to the access, by all people at all times, to adequate, safe and nutritious food for a healthy and productive life. Food security may be influenced by the following factors:
Exponential growth of the human population
- The world’s population is growing at an exponential rate (very rapidly) and as a result some countries cannot produce enough food to feed their growing population. Food production needs to increase as rapidly as the world population; otherwise many countries will experience food insecurity.
Droughts and floods
- Climate change has led to more frequent and severe droughts and floods. Droughts result in crop losses and livestock death which reduce the food available in an area. Floods cause extensive damage in a short period of time and decrease the amount of farmland available to grow crops. People also usually lose their homes, possessions and economic security during floods, further impacting on food security
Poor farming practices – monoculture, pest control, loss of topsoil and the need for fertilizers
- Monoculture is the growing of one type of crop over large areas of land year after year. Monoculture depletes nutrients and water supplies and therefore impacts negatively on the quality of the topsoil.
- Pest control involves the use of pesticides (chemicals) to kill pests that compete with humans for food. Pesticides may kill or get into the tissues of healthy plants. This may reduce crop production and, since pesticides are expensive, increase the cost of food and thus reduce access to poor consumers. Many farmers now use biological control, which uses a natural predator/parasite to get rid of the pest instead of using expensive pesticides.
- Topsoil is the top 1.5 metres of soil that contain the nutrients that plants require for growth. The tilling of the soil between plantings and heavy rainfall cause much of the topsoil to be lost, leading to the loss of valuable nutrients over time, reducing crop yields.
- The use of fertilizers, both inorganic (chemical) and organic (compost and manure) can increase the nutrients in the soil and keep soil fertile. This replaces nutrients in the soil that are lost when crop plants absorb them. Fertilizers can be expensive, contributing to the high cost of food, thus reducing access to poor consumers.
Alien plants and reduction of agricultural land
- Alien plants deplete the topsoil of water and nutrients. These alien plants out-compete indigenous plants because they have no natural predators, grow rapidly and invade land that could be used to grow crops.
The loss of wild varieties and the impact on gene pools
- Crop plants have replaced wild varieties. The preservation of wild varieties is important because, if changing environmental conditions destroy the present crop plants, then wild varieties could be used as alternative sources of food. If wild varieties are wiped out, it will reduce the genetic diversity and thus the gene pool.
Genetically engineered food
- Genetically engineered food is produced from genetically modified organisms (GMOs). Genetic engineering involves the inserting of a gene (with a desired characteristic) from one organism into another organism to increase the yield. For example, a gene for drought resistance could be inserted into a crop plant that grows in areas where water is scarce.
Food wastage
- Wastage could occur during the storage, production and processing of food. Wastage includes food thrown away and food not eaten.
Wastage increases the prices of food to consumers and could reduce food security in a country.
Loss of biodiversity
Biodiversity refers to the variety of plant and animal species on Earth.
Factors that reduce our biodiversity
Farming methods
- Monoculture : Monoculture is the growing of one type of crop over large areas of land year after year. Monoculture replaces indigenous plants and reduces biodiversity. Insects that specialise in feeding on one type of crop spread rapidly because there are no natural enemies or barriers to stop them. This means the farmer needs to use more pesticides to kill them. Intensive use of agrochemicals such as fertilisers and pesticides often end up in rivers, streams and groundwater, poisoning species in the area and causing eutrophication. This results in a large loss of biodiversity. Overgrazing: It occurs when livestock such as sheep or cattle are kept in an area for too long; the vegetation is grazed to a point where it will not grow back. It causes soil erosion by removing the plants that bind the soil together with their roots. Topsoil is lost during rainstorms. This can lead to the extensive destruction of land through desertification which results in loss of biodiversity. Sometimes overgrazed land becomes subject to alien plant invaders which destroy habitats by taking over the land.
Golf Estates
Developments such as golf estates are a form of monoculture that requires large amounts of water, pesticides and fertilisers which may runoff and poison aquatic ecosystems. Housing associated with golf developments replaces large areas of natural vegetation.
Mining
- Mining alters the environment and can negatively affect the biodiversity in an area. Pollutants in the form of dust and smoke may be released into the air while vegetation is removed and replaced with rock and waste dumps. Underground water may be poisoned because of sulphates and heavy metals released into them.
- Urbanisation The growth of large cities (urbanisation) also negatively impacts on biodiversity. Surfaces are covered with concrete, and natural habitats are destroyed to build houses and businesses. Habitat fragmentation causes the loss of biodiversity, as natural plants are replaced by exotic trees and plants.
Deforestation
- Deforestation is the permanent destruction of indigenous forest and woodland areas. Deforestation is caused by human activities such as agriculture, logging, and using trees as firewood. Deforestation leads to the destruction of the habitats of other organisms, like frogs and insects, and this leads to the loss of biodiversity.
Loss of wetlands and grasslands
- Grasslands and wetlands have unique plant and wildlife and provide many ecological services to humans. Destruction of these habitats will lead to the loss of species.
Poaching
- Poaching refers to the illegal hunting of animals, either for food or because certain body parts can be sold for money. ‘Poaching’ may also be applied to plants that are removed and sold for profit e.g. medicinal plants. Some wild animals are hunted for food (‘bush meat’) and are on the verge of extinction. Elephants are poached for their tusks to make carvings and jewellery and rhinos are hunted for their horns which are used in the Far East for medicinal reasons.
- Alien plant invasions These plants are species that have been introduced into an area and which compete with the natural plants in the area. They can outcompete indigenous plants, thus reducing the biodiversity.
Ways in which our biodiversity can be maintained
Control of alien plant invasions
Alien invasive species may be controlled by mechanical, chemical and biological methods. Mechanical methods involve chopping down plants or physically removing them by hand and is very time consuming. Chemical control involves spraying herbicides onto the plants; this can pollute the environment and is expensive. Biological methods involve introducing a natural enemy from the alien plant’s environment and allowing it to reproduce and feed on the invasive plant.
Sustainable use of the environment
Sustainable use of the environment means using resources without harming the ability of future generations to use that resource. Substances from indigenous plants such as the African potato, Hoodia, rooibos and Devil’s claw all have economic and medicinal value. These indigenous plants can be used sustainably by encouraging traditional healers to grow their own plants and through improving education of the women who generally gather the plants in the wild.
Encouraging traditional healers to be part of formal medical programmes would encourage training to be ongoing and help establish sustainable use of medicinal plants. Legislation should be passed to limit the numbers of plants that can be harvested at one time and seeds of medicinal plants could be collected and distributed to increase plant numbers.
back
Dihybrid Crosses
A Dihybrid cross refers to a cross where two set of characteristic are inherited.
Remember with a dihybrid cross we have two separate traits and we want to show that these traits undergo independent assortment one of mendels laws.
To begin will start with a Key.
TT = tall
Tt = tall
tt = short
RR = red
Rr = red
rr = yellow
To Solve a dihybrid cross you have to start with a key to show you understand the pattern.
After you do the cross.
For example : Heterzyous tall plant and red seeds with another x
Heterzyous tall plant and red seeds.
So the Genotype will be ( TtRr x TtRr)
So now will have to draw a 8 by 8 plate square.
Now we need to determine what allels each of the plants need to put in their gametes.
TR | Tr | tR | tr | |
---|---|---|---|---|
TR | TTRR | TTRr | TtRR | TtRr |
Tr | TTRr | TTrr | TtRr | Ttrr |
tR | TtRR | TtRr | ttRR | ttRr |
tr | TtRr | Ttrr | ttRr | ttrr |
Do you see the pattern...
TR | Tr | tR | tr | |
---|---|---|---|---|
TR | TTRR | TTRr | TtRR | TtRr |
Tr | TTRr | TTrr | TtRr | Ttrr |
tR | TtRR | TtRr | ttRR | ttRr |
tr | TtRr | Ttrr | ttRr | ttrr |
Genotype
- TTRR (1/16)
- TTRr (2/16)
- TTrr (1/16)
- TtRr (2/16)
- TtRr (4/16)
- Ttrr (2/16)
- ttRR (1/16)
- ttRr (2/16)
- ttrr (1/16)
Phenotype
- (9/16) Tall and red
- (3/16) Tall and yellow
- (3/16) Short and red
- (1/16) Short and yellow
Mendel's Experiments
Gregor Mendel, was an Austrian monk who carried out breeding experiments with garden peas from 1857 to 1864
Monks had a lot of time on there hands and mendel spent his time crossing pea plants. As he did this over and over again, he noticed some patterns to the inheritance of traits from one set of pea plants to the next. By carefully analyzing his pea plant numbers (he was really good at math), he discovered three laws.
Mendel's Laws are as follows
- The Law of Dominance
- The Law of Segregation
- The Law of Independent Assortment
The Law of Dominance
The Law of dominance states that only one trait in a pair will be dominate and therefor show up in the Phenotype unless the pairs are recessive
e.g Tall(T) x Short(t)
= Tall(Tt)
The Law of Segregation
The Law of Segregation states that members of a pair of homologous chromosomes separate during the formation of gametes and are distributed to different gametes so that every gamete receives only one member of the pair
The Law of independent Assortment
The Law of independent Assortment states that each member of a pair of homologous chromosomes separates independently of the members of other pairs so the results are random
Three types of Dominance
- Complete dominance
- Incomplete dominance
- Co-dominance
Complete dominance
A genetic cross where only one allele is dominant over the other allele and therefore only the dominant one is expressed in the phenotype.
Example :
P1
Genotype = RR x rr
Phenotype = Red x white
meiosis
G1
R | R | |
---|---|---|
r | Rr | Rr |
r | Rr | Rr |
F1
Genotype = 4(Rr)
Phenotype = 4(Red)
Incomplete dominance
A genetic cross where none of the allele's are dominance over the other and therefore none of them are expressed in the phenotype.
Example :
P1
Genotype = RR x rr
Phenotype = Red x white
meiosis
G1
R | R | |
---|---|---|
W | RW | RW |
W | RW | RW |
F1
Genotype = 4(RW)
Phenotype = 4(Pink)
Co-dominance
A genetic cross where both of the alleles are dominant over each other and are therefore are both expressed in the phenotype.
Example :
P1
Genotype = RR x rr
Phenotype = Red x white
meiosis
G1
R | R | |
---|---|---|
W | RW | RW |
W | RW | RW |
F1
Genotype = 4(RW)
Phenotype = 4(Equal colours both red and white)
Blood types
In humans you find only three types of blood groups
Blood type can also be used to determine parentage but since many people have the same blood group it not be useful
• A
• B
• O

An individual can only have two of these alleles making up his/her genotype
The i alleles is recessive to the |A , |B. These alleles are co-dominant
Understanding these group types
|A and |B = are co-dominant
|A is dominant = over i
|B is dominant = over i
ii are just two recessive alleles
Example : Crossing a homozygous parent with blood type A and heterozygous blood type B parent
P1
Genotype = |A |A x |B i
Phenotype = Homozygous A blood type x Heterozygous B blood type
meiosis
G1
|A | |A | |
---|---|---|
|B | |A |B | |A |B |
i | |A i | |A i |
F1
Genotype = 2(|A |B) 2(|A i)
Phenotype = 2(With AB blood type) and 2(with A blood type)
Mutations
Mutations means sudden, changes in the genetic code of an organism which can be inherited.
Causes of mutations
Mutations occur suddently and randomly and may be caused by many environmental agents such as X-rays, cosmic rays, ultra-violet radiation and certain chemicals.
Where does mutation occur
- Somatic cells and sex cells
- When they occur in somatic cells they results in disorders such as cancer
- When they occur in sex cells they can be inherited
Two Types of Mutations
- Gene mutations
- Chromosomal Aberrations
Gene mutations
A gene mutation refers to a change in the structure of a gene as a result of a change in the DNA sequence.
Types of Gene mutations
Point Mutations

- In point mutation, there is a change in a single base pair in the DNA molecule at just one point (i.e. a single base pair is replaced by another base pair).
Frame-shift Mutations
- A single base pair may be inserted or deleted from the DNA molecule.
Chromosomal Aberrations/Chromosomal Mutations
- Chromosomal Aberrations refers to changes in the normal structure or number of chromosomes
Types of Chromosomal Aberrations

- Deletions : In Which a section of a chromatid is simply lost
- Duplications : In which a section of a chromatid is doubled
- Inversions : In which a section of a chromatid gets turned
- Translocations : In which a part of the chromatid amy break off and join a non-homologous chromosome.
Effects of mutations
You find Harmful mutations and Harmless mutations
Harmful Mutations
Harmful mutations are also called lethal mutations, the mutated organism dies along with the mutations, so the characteristic is not past on to the next generation.
Harmless Mutations
There are two types of harmless mutations
- Neutral mutations
- Advantageous mutations
Neutral mutations
Neutral mutations have no effect on the organism they affect, meaning it normal to have the mutations.
Advantageous mutations
Advantageous mutations are actually an advantage to the organism they affect meaning that they may offer special abililties which normal organism may be incapable of doing.
Sex Determination in Humans
As you know XX represents a Female and XY represents a Male
Males have a single X-chromosome + (22 pairs of autosomes)
Autosomes: All chromosomes besides the sex chromosomeFemales have two X-chromosomes + (22 pairs of autosomes)
How to determine sex in humans
P1
Genotype = XX x XY
Phenotype = Female x Male
meiosis
G1
X | X | |
---|---|---|
X | XX | XX |
Y | XY | XY |
F1
Genotype = 2(XX) 2(XY)
Phenotype = 2(Females) 2(Males)
Percentage = 50%(female) 50%(male)
This means that there is a 50:50 chances that the offsprings will be male or female.
Now representing the inheritance of sex-linked charateristics in a genetic cross
Lets make an example of haemophilia ,a genetic disorder which affects mostly males
Key note to understand
Females
XH XH =normal blood (Homozygous normal female)
Xh X h =haemophilia (Homozygous haemophilia female)
XH Xh =normal blood (carrier) (Heterzygous normal female)
Males
XH Y = normal blood
Xh Y = haemophilia
HH doesn't have haemophilia and not even a carrier
Hh doesn't have haemophilia but a carrier
hh has haemophilia and also a carrier
In Males the Y-Chromosome will never be normal and carriers
Example: What will happen when a Heterzygous normal Female cross with a normal male
XH |
Xh |
|
---|---|---|
XH |
XH XH |
XH Xh |
Y |
XH Y |
Xh Y |
F1
Genotype
XH XHXH XhXH YXh YPhenotype
1 = Normal blood female
1 = Normal blood (carrier) female
1 = Normal blood male
1 = haemophilia male
Genetic disorders caused by Mutations
The following disorders are also known as sex-linked disease as they are inherited.
- Down syndrome
- Sickle-cell anaemia
- Haemophilia
- Albinism
Down syndrome
Causes
Down syndrome is cause by an extra copy of chromosome 21. They are 3 copies instead of 2. Remembers this also is called trisomy 21.
Symptoms
- Mental retardation
- Hearing loss
- Decreased muscle tone
- Upwardly slanting eyes
- Small mouth
- Abnormal ear shape
- Small nose
Sicle-cell anaemia
Causes
Sickle-cell anaemia is caused by a mutant allele on chromosome number 11. Sicle-cell cause the red blood corpuscle to become sickle shaped.
Symptoms
- Redued blood supply
- Damage to organs such as the spleen
- Damageed parts of the brain
- suddent pains
Treatment
- Blood transfusions and drugs may help to reduce pain.
- Bone marrow transplant
Haemophilia
A person suffering from haemophilia has hard time clotting his/her blood which may result in mass blood loss
Causes
Its caused by a recessive allele on the X-chromosome
Symptoms
- Blood does not clot well
- Internal bleeding at joints which may lead to arthritis
- Bleeding to death without treatment
Treatment
- Injection of purified clotting agents extracted from human blood plasma
Albinism
A person who is suffering from albinism lacks a pigment called melanin.
Causes
Caused by a mutation of a gene on the X-Chromosome.
Symptoms
- Poor vision
- light skin which gets sunburns very easily
- Skin highly susceptible to skin cancer
Treatment
- Sunscreen to reduce skin burns
- eye glass to enhance vision
Genetic Engineering
Genetic engineering, also called genetic modification is to change the characteristics of an organism by manipulating its genetic material.
Cloning is a type genetic engineering, where the aim is to duplicate the genes of an existing individual so that an identical set is inside an egg.
The use of stem cells to treat disease, like cloning, is alos a type of engineering but is not the same as true genetic manipulation.
Genetically Modified Organisms
- The first genetically modified organisms were bacteria in 1973
- Plant can also be modified so that they become bigger and resistant to dieases.
- Pest resistant and drought resistant plants
- Cheaper production of medication or other resources
- Increased crop yield's therefor increased food security
Arguments against genetic modification
- Expensive
- Interfering with nature
- unkown long term effects to human health
Pedigree Diagrams
A pedigree diagram is used to study the inheritance of characteristics in a family over a number of generations. A pedigree diagram is also called a family tree.
Steps when interpreting pedigree diagrams:
- Step 1 : Study any key and opening statement/s and look for dominant and recessive characteristics and phenotypes.
- Step 2 : Write in the phenotypes of all the individuals as given in the problem.
- Step 3 : Fill in the genotype of all the individuals with the recessive condition – it must have two
recessive alleles (two lower case letters, e.g. ff).
- Step 4 : For every individual in the diagram that has the recessive condition, it means that each allele was obtained from each of the parents. Work backwards and fill in one recessive allele for each parent.
- Step 5 : If the parents showed the dominant characteristic, fill in the second letter which represents the dominant allele (a capital letter, e.g. F).
- Step 6 : Any other individual showing the dominant characteristic will most likely be homozygous dominant (FF) or heterozygous dominant (Ff).
Now lets do an example
Brown eye colour (B) is dominant over blue eye colour (b).
Our pedigree

Genetic counselling
Couples with a risk of giving birth to children with genetic diseases can undergo genetic counselling to enable them to make informed decisions on whether they want to have children or not.
Benefits of genetic counselling
- To be given advice on the risk of transferring the defective gene/ to find the probability of passing on the defective gene to the offspring
- To be given an explanation of the procedure involved in DNA testing
- To be given an explanation of the results of DNA testing
Nervous Tissue
Nervers are made up of nerver fibres held togther by connective tissues.
The nerver fibres on the other hand are made up of specialized nerver cells
called Neurons.
Neurons are specialised cells which connect the brain and spinal cord to all other parts of the body.
Three types of Neurons

- Sensory neurons
- Motor neurons
- Connector neurons/interneurons
Sensory nenron
- Carries impulses from the receptors to the central nevrous system
Motor nenron
- Carries impulses from the central nervous system to the effectors
Connector nenron
- Carries impulses inside the central nervous system from a sensory neuron to a motor nenron
Parts of the neuron definination
- Dendrite: Transmits impulses towards the cell body of the neuron
- Axon: Transmits impulses away from the cell body of the neuron
- Myelin sheath: provides electrical insulation and helps to speed up up the transmission of impulses.
Synapse
A microscopic gap between the axon terminals of one neuron and the dendrite of another.
Neurotransmiitters
Carries nerve impulses from one dendrite to another.
The main parts of the Nervous System
The Nervous system is divide into two main parts
- Central nervous system
- Peripheral nervous system
Central nervous system includes
- The Brain
- Spinal Cord
Peripheral nervous system
Is made up of all the nerves outside the central nervous system
- Somatic nervous system
- Autonomic nervous system
Its further sub-divided into
Somatic nervous system
Includes parts of the nerves system that enables the body to react to changes in the external environment.
Autonomic nervou system
Includes parts of the nerves system that control the internal enivornment. e.g (actions of sweating, and the heart and breathing rates.)
The Central Nervous System
The central nervous system consists of the brain and the spinal cord
The structure and functions of The Brain

Cerebrum
- Controls voluntary actions
- Receives and interprets sensations from sense organs
- Higher thought processes
Medulla oblongata
- Transmits nerve impulses between the spinal cord and the brainr.
- Controls involuntary actions such as heartbeat and breathing
Hypothalamus
Control centre for hunger, thirst, sleep, body temperature and emotionsCerebellum
- Coordinates all voluntary movements
- Controls muscle tension to maintain balance

The Spinal Cord
- The spinal cord is an elongated cylinder-like structure running in the vertebral canal formed by successive vertebrae.
- The spinal cord is protected by the meninges
- The spinal cord consists of white matter on the outside and grey matter on the inside.
Functions of the spinal cord
- It conducts impulses between the brain and the receptors and effectors
- It serves as a reflex centre for actions such as blinking, sneezing, coughing and knee jerk
Reflex action and Reflex arc


A reflex action is a quick, automatic response to a stimulus received by an organ or other receptor.
The reflex arc is the path along which an impulse is transmitted to bring about a response to a stimulus during a reflex action.
Reflex arc
The path taken by an impulse to bring about a response to a stimulus during a reflex action.
The path of a reflex arc:
Receptor (A) → Sensory neuron (B) → Interneuron (C) → Motor neuron (D) → Effector (E)
The reflex action

- Receptor: A structure which receives a stimulus and converts it into an impulse (the heat sensor of the finger feels burn)
- Sensory neuron: Carries the impulse from the receptor to the spinal cord
- Effector: A structure which produces the reaction (the muscles in the finger contract and the finger is pulled away)
- Interneuron: Carries the impulse from sensory neuron to the motor neuron in the spinal cord
- Motor neuron: Carries the impulse from the spinal cord to the effectors
Disorders of the central nervous system
Alzheimer's disease

Is a diseases that occurs when the nerve tissue within the brain appears to waste away.
Symptoms
- Memory loss
- Confusion
Multiple sclerosis

When the bodys own immune system attacks and destroys the myelin sheath causing a disorder called multiple sclerosis.
Symptoms
- Physical disabilities
- Mental disabilities
Effects of drugs
Dagga (Marijuana or Cannabis)
- Affects the parts of the barin that control emotions ,memory and judgment
- Weaken short-term memory and block information from becoming save into long trem memory
Heroin
- Gives an immediate 'rush ' of pleasure but leaves the brain in a 'fog' for many hours afterwards
- Difficulty in differentiating reality and fantasy
Ecstasy
- Difficulty in differentiating between reality and fantasy
- Problems in concentration
Tik
- Paranoia ,anxiety,fearfulness and exhaustion
- Memory loss ,mood swings,wild rages
Alcohol
- Impairs judgment and leads to to memory lapses
- Can damage every organ in the body,including the brain
Cocaine
- Loss of interest in many areas of life ,including school ,sports,family ,and friends
- paranoia and anxiety
The human eye

Structure of the ear and function
- Retina : Contains the light-senstive receptor cell
- Sclera: The tough white outer coat ,which protects the eye against damage
- Choroid: Reduces reflection ,Supplys cells with nutrients and oxygen
- Yellow spot : Has the greatest number of cones, this area offers the clearest image
- Optic nerve: Carries nerve impulses from the retina to the brain
- Blind spot : This area has no rods and cones ,therefore there is no vision at this point
- Vitreous humour: A jelly-like substance which gives shape of to the eye
- Lens: Changes shape for near and distant (far) vision
- Lris: The coloured part of the eye
- Aqueous humour: Watery fliud that supports the cornea and fronts chamber of the eye
- Pupil: A circular opening in the iris which allows light into the eye
- Suspensory ligament: Holds the lens in position
Accommodation

Is the adjustment of the shape lens to see clearly whether away or close by.
Distant vision (objects further than 6m)
- 1.Ciliary muscles relax
- 2.Suspensory ligaments tighten (become taut)
- 3.Tension ligaments tigten (become taut)
- 4.Lens is less convex (Flatter)
- 5.Light rays are refracted (bent)less
- 6.Light rays are focused onto the retina
Near vision (objects closer than 6)
- 1.Ciliary muscles contract
- 2.Suspensory ligments slacken
- 3.Tension on lens decreases
- 4.Lens becomes more convex (more rounded)
- 5.Light rays are refracted (bent) more
- 6.Light rays are focused onto the retina
Pupillary mechanism

The pupillary mechanism (or pupil reflex) regulates the amount of light entering the eye by adjusting the size of the pupil
Light is briht
- 1.Radial muscles of the iris relax
- 2.Circular muscles of the iris contract
- 3.Pupil constsricts (gets smaller)
- 4.Less light enters the eye
Light is dim
- 1.Radial muscles of the iris contract
- 2.Circular muscles of the iris relax
- 3.Pupil widens (gets bigger)
- 4.More light enters the eye

Diseases and Disorders of the Eye

- Long-sightedness (Hypermetropia)
- Short-sightedness (Myopia)
Long-sightedness (Hypermetropia)
- Inability to see near objects less than 6 metres
How to correct
- Wearing glasses with convex lenses
Short-sightedness (Myopia)
- Inability to see distant objects less than 6 metres
How to correct
- Wearing flasses with concave lenses
Structure of the ear

Functions of the ear
- Pinna: Directs sound waves to eardrum
- auditory canal: Transmits sound waves to the eardrum
- Tympanum (eardrum): Transmits sound waves to the middle ear
- Ossicles: Transmit vibrations from the eardrum to inner ear
- Eustachian tube: Equalises pressure on either side of the eardrum
- Oval window: Transmits sound waves to the inner ear
- Round window: Releases pressure from the inner ear
- Semi circular canals: Balance of the body
- Sacculus and utriculus: Balance of the body
- Auditory nerve: Transmits impulses to the brain
- Cochlea: Contains the organ of Corti which converts sound waves into nerve impulses
Hearing

- Sound waves are directed into the auditory canal by the pinna.
- The sound waves make the tympanic membrane vibrate and the vibrations are passed on to the ossicles in the middle ear.
- The ossicles make the oval window vibrate and this causes pressure waves to be set up in the inner ear.
- These vibrations also cause the organ of Corti to be stimulated and it generates impulses which are sent to the cerebrum along the auditory nerve.
- The cerebrum interprets the impulses as sound.
Balance
- Random changes in the speed and direction causes the endolymph inside the semicircular canals to move.
- This also causes fluids inside the semicircular canals to move.
- The movement of the fluids stimulates the receptors called cristae within the ampullae
- When the direction of head changes, gravitational pull stimulates different receptors called maculae, within the sacculus and utriculus
- The cristae and maculae (stimuli) are converted to nerve impulses
- These impulses are transmitted by the vestibular branch of the auditory nerve to the cerebellum
- The cerebellum sends impulses to the muscles to restore the balance
Diseases and Disorders of the Ear
- Middle ear infection
- Deafness
Middle Ear Infection
Is caused by bacteria
Treatment
- Insert grommets
- Antibiotics
Deafness
Is caused by damages to certain parts of the ear
Treatment
- Hearing Aid
- Cochlear implants
What is an Endocrine System ?
Our bodies consist of two kind of glands:
- Endocrine glands
- Exocrine glands
Exocrine glands
Consist of ducts, e.g sweat ducts which carry secretions to the surface of the skin
Endocrine glands
Produces secretions that have to be transported for use far away from the gland itself e.g (Pituitary gland or hypophysis).
Hormones
Hormones are organic chemical messengers.
The human endocrine system
- The endocrine system is responsible for chemical coordination and regulates activities that take place inside the body.
- The endocrine system consists of glands that produce different hormones, which are the body's chemical messengers.

Hypothalamus
- Target organ: Kidney
- Controls the concentration of water in the blood
ADH (antidiuretic hormone)
Thyroid gland
Thyroxin
- Controls basic metabolic rate
Adrenal gland
- heartbeat
- blood pressure
- conversion from glycogen to glucose
- blood supply to the cardiac and skeletal muscles
- skeletal muscle tone
- rate and depth of breathing
- diameter of pupils
- blood flow to the digestive system and skin Aldosterone
- Target organ: Kidney
- Regulates salt concentration in the blood
Adrenalin
Increases:
Decreases:
Ovary (only females)
- Prepares the wall of the uterus by making it
- Thicker, vascular and full of blood
- Maintaince pregnancy
Oestrogen
Progesterone
Testes (only males)
- Development of male secondary sexual characteristics
- Stimulates the maturation of sperm cells
Testosterone
Pancreas: Islets of Langerhans
- Stimulates conversion of glycogen to glucose (increases blood glucose levels)
- Stimulates conversion of glucose to glycogen (reduce
Glucagon
Insulin
Pituitary gland (hypophysis):
- Controls growth
- Stimulates thyroid gland to secrete thyroxin
- Stimulates the production of milk by the mother
- Causes a follice in the ovary to become a Graffian follice
- Converts raputured Graffian follice to corpus luteum
GH (growth hormone)
TSH (thyroid stimulating hormone)
Prolactin
FSH
LH
Negative feedback mechanisms
Operate in the human body to detect changes or imbalances in the internal environment and to restore the balance.
In other words if theres any changes in the body that are above normal the body release certain hormone to ensure that the body goes back to its normal form

How the negative feedback mechanisms works ?
- Step 1: An change is detected.
- Step 2: A control centre is stimulated.
- Step 3: Control centre responds
- Step 4: Message sent to target organ/s
- Step 5: The target organ responds.
- Step 6: It opposes/reverses the imbalance.
- Step 7: Balance is restored
Example : Thyroxin Level increase above normal
- Step 1: When thyroxin level increase above normal.
- Step 2: Pituitary gland is stimulated.
- Step 3: Pituitary gland produces less TSH.
- Step 4: TSH stimulates the thyroid gland.
- Step 5: Thyroid secretes less thyroxin.
- Step 6: Thyroxin level therefore decreases.
- Step 7: Thyroxin level goes back to normal
Example : Thyroxin Level decrease above normal
- Step 1: When thyroxin level decrease above normal.
- Step 2: Pituitary gland is stimulated.
- Step 3: Pituitary gland produces more TSH.
- Step 4: TSH stimulates the thyroid gland.
- Step 5: Thyroid secretes more thyroxin.
- Step 6: Thyroxin level therefore increases.
- Step 7: Thyroxin level goes back to normal
We will look at other examples when we do homeostatsis
Diabetes
Diabetes is caused when the body can no longer produce insulin therefore the glucose level of the blood rises.
There are two types of Diabetes
Type 1 diabetes
Occurs when the pancrease stops producing insulin.
Type 2 diabetes
Occurs when the insulin produced isn't enough or not functioning properly.
Symptoms
- Extreme thirts
- bured vision
- Weight loss
- non-healing of wounds
Treatment
- Excerise
- Eating healthy
What is Homeostatsis ?
This enables the body to function efficiently ,despite changes in the external or internal environment
Negative feedback mechanisms
- The level of glucose ,carban dioxide ,water and salt levels amongst others need to be kept constant, within narrow limits, this means that the negative feedback mechanisms must work constantly also.
Maintaining the blood/sugar glucoso level

Increases
- Step 1: When glucose Level increase above normal.
- Step 2: Islets of Langerhans secretes Insulin.
- Step 3: Insulin decreases the glucose level.
- Step 4:Glucose Level than goes back to normal.
Decrease
- Step 1: When glucose Level decrease above normal.
- Step 2: Islets of Langerhans secretes Glucagon.
- Step 3: Glucagon increases the glucose level.
- Step 4:Glucose Level than goes back to normal.
Maintaining Oxygen and Carbon Dioxide Levels
Increases
- Step 1: When Carbon Dioxide Level increase above normal.
- Step 2: Medulla oblongata increases heartbeat and breathing rate.
- Step 3: Carbon Dioxide is expelled for the body and more Oxygen is taken up the lungs and sent to the cells.
- Step 4: Carbon Dioxide Level in the body decreases.
Maintaining water levels (Osmoregulation)

When the body has too much water
- Step 1: When water Level increase above normal.
- Step 2: The Pituitary gland secretes less ADH.
- Step 3: Less water is then re-absored so more water is lost in urine.
- Step 4: Water Level in then body decreases and goes to normal.
When the body has too little water
- Step 1: When water Level decrease above normal.
- Step 2: The Pituitary gland secretes more ADH.
- Step 3: More water is then re-absored so less water is lost in urine.
- Step 4: Water Level in then body increases and goes to normal.
Maintaining salt/soduim levels
When the body has too much salt
- Step 1: When sodium Level increase above normal.
- Step 2: The Adrenal gland secretes less aldosterone.
- Step 3: Less sodium is re-absored so more sodium is lost in urine.
- Step 4: Sodium Level in then body decreases and goes back to normal.
When the body has too little salt
- Step 1: When sodium Leveldecrease above normal.
- Step 2: The Adrenal gland secretes more aldosterone.
- Step 3: More sodium is re-absored so less sodium is lost in urine.
- Step 4:Sodium Level in then body increases and goes back to normal.
The process of temperature regulation
- Hypothermia: occurs when the body temperture drops below 37*C for an extended time . it is caused by exetended exposure to cold conditions .More heat is lost than the body is able to produce.
- Hyperthemia: occurs when the body temperture increases above 37*C for an exetended time . it is caused by prolonged exposure to high temperatures. The body produces and absorbs more heat then it can lose.
Temperature regulation is the control of body temperature to keep it as close to 370C as possible to enable the body to function normally
Body temperature is regulated by the hypothalamus in the brain and the blood vessels and sweat glands in the skin.
On a hot day

- Step 1: Heat receptors in the skin are stimulated.
- Step 2: The stimulus is converted into an impulse and transmitted to the hypothalamus.
- Step 3: High blood temperature also stimulates the hypothalamus directly.
- Step 4: Nerves impluse are sent from the hypothalamus to the muscles of the blood vessels of the skin .
- Step 5: The blood vessels to the skin dilate ( this is called vasodilation).
- Step 6: More blood is sent to the surface of the skin and more heat is lost from the body.
- Step 7: More sweat is producted and more heat is lost by evaporation of sweat.
- Step 8: The temperature of the body drops back to normal body temperature.
On a cold day

- Step 1: Cold receptors in the skin are stimulated
- Step 2: The stimulus is converted into an impulse and transmitted to the hypothalamus.
- Step 3: low blood temperature aslo stimulates the hypothalamus directly.
- Step 4: Nerve impulses are sent from the hypothalamus to the muscles of the blood vessels of the skin.
- Step 5: The blood vessels to the skin constrict ( this is called vasoconstrition)
- Step 6: Less blood is sent to the surface of the skin and hence less heat is lost from the body
- Step 7: Less blood is also sent to the sweat glands
- Step 8: Less sweat is formed and less heat is lost by the evaporation of sweat
- Step 9: The temperature of the body rises back to the normal body temperature of the body rises back to the normal body temperature.
Structure of the Skin

Plant Growth Substances
A hormone is an organic substance produced in small amounts in one part of the body and transported to other parts where it controls the growth and development in some specific way. Auxins, gibberellins and abscisic acid are some examples of plants growth substances that may be considered to be horomones
The Three types of plant Hormones
- Auxins
- Gibberellins
- Abscisic Acid
Auxins

- Brings about a bending reaction in plants known as tropism.
- Promote cell division
- Responsible for cell enlargement
- Promote root development
- Responsible for plant growth
Gibberellins
- Brings about elongation of the internodes of stems.
- stimulates root growth
- Promote development of flowers
- Helps in the germination of seeds
- Increases fruits size.
Abscisic Acid

- Brings about dormancy of seeds by slowing down germination, and dormancy of apical buds.
- Induces flowering in some plants
- Helps in the closing of stomata during periods of water shortage or drought
- Promotes the ageing of Leaves
Phototropism and Geotropism
A tropism is a growth movement or bending reaction of a plant (or part of a plant) in response to an external stimulus.
- The direction of growth or bending of the plant depends on the direction of the stimulus.
- When the external stimulus is light, this is known as phototropism.
- If the external stimulus is gravity, this is known as geotropism.
Phototropism

Is the growth movement of plant organs in response to the stimulus of light.
- Stems are positively phototropic i.e they growth towards light.
- Roots are negatively phototropic i.e they grow away from light.
Geotropism

Is the growth movement of plant organs in response to the stimulus of gravity.
- Roots are positively geotropic while stems are negatively geoptropic.
Role of auxins in Phototropism

- Auxins are produced at the tip of the stem from where they move downwards evently.
- The even distribution of auxins brings about equal growth on all sides of the stem.
- Therefore, the stem grows straight upwards.
- When stems are exposed to unilateral light(light from one side) the brightly-lit side suffers from a shortage of auxins probably because the auxins are destroyed by the light or because they move to the darker side.
- A high concentration of auxins in stems promotes growth.
- Thus an uneven distribution of auxins causes uneven growth of the stem with the darker side growing faster
- The stem thus bends towards the light i.e stems are positively phototropic.
Role of auxins in Geotropism

- Auxins are produced at the tip of the root from where they move upwards evently.
- The even distribution of auxins brings about equal growth on all sides of the root.
- Therefore, the stem grows straight downwards.
- When a root is placed horizontally the auxins accumulate on the lower side probably because of gravity.
- A high concentration of auxins in roots inhibits growth.
- Thus an uneven distribution of auxins causes uneven growth of the root with the upper side growing faster.
- The root thus bends downwards i.e roots are positively geotropic.
Weed Control by using Growth Hormones
- Hormone weed-killers are auxin-based selective herbicides, which are pesticides that kill only one specific unwanted plant as they are used in the appropriate dosage.
- Hormone weed-killer is made by chemical synthesis and are the main factor in controlling weed growth.
Advantages of Hormone weed-killers
- Non-Toxic to Animals or Humans.
- Eliminate the need to hand pick annoying unwanted weeds in the garden.
Disadvantages of Hormone weed-killers
- May damage other plants if over used.
- Can affect plant growth.
Plant Defence Mechanism
This deals with how the plant protects itself from being eaten by other animals/inserts.
Plants protect themselves using chemicals and thorns
- Some plants have thorns on their stems and leaves.
- These thorns serve as protection and keep herbivoures at bay
- Plants that use chemical defense secrete poisonous chemicals that may kill many organisms.
- Many organisms avoid theres plants.
Thorns
Chemicals
Hypothesis and Theory
In science a Theory is an idea that has been well tested and shown to be widely applicable, preferably one that has not been falsified by a better 'theory'.
AndIn science a Hypothesis is an untestable idea that cannot be falsified at the time, but would explain a great deal of great importance if true.
What is Evolution ?

The theory of evolution states that all the things we see today arose from things that existed in the past but they look different because things change over long periods of time.
Biological evolution is a special type of evolution that refers to changes that living things have undergone over long periods of time.
Simple english
- The theory of evolution states that everything we see today living, came from things that have lived before , along time ago, but now they look different from them because thing change over long periods of times.
Variation within a species
Species
- refers to a group of similar organisms that are able to interbreed to produce offsprings , that will be able to interbreed.
Population
- refers to organisms of the same species living in the same area at the same time, and can interbreed.
Variation
- refers to the small differences that exist between individuals of a species or population (e.g) differences in height, differences in eye colour etc..
Sources of variation
Things that bring about change amongst species(organisms).
- Mutations involves a change on the structure of a gene.
- During Prophase 1 chromosome exchange genetic material bring about variation.
- During Metaphase 1 and Metaphase 2 Chromosomes/chromatids align themselves in equator at random positions bring about variation
- Every egg cells and sperm cells produced during meiosis are different form each other. Since there is random fertilisation of these gametes, there will be different combinations of genetic material in the offspring.
1) Mutation
2) Meiosis
-
Crossing-over
Random arrangement of chromosome
3) Random fertilisation of gametes
Continuous and Discontinuous Variation

Continous variation
In continous variation, variation is endless there is a range of different phenotypes for a particular characteristic. Example lets look at the height of a human , we can see that there is a complete range of measurements.
Discontinuous variation
In discontinous variation, there is no range of different phenotype its (either this or this) for a particular characteristic. Example Human blood Group it either A, B ,O or AB
Evidence for Evolution
Previously you learnt that according to the theory of biological evolution, all organisms we see today came from organisms that existed in the past but they look different today because things change over time.
For scientists to determine if two species are closely related to each other or have a common ancestor, they must study the characteristics of the species concerned.
Scientist provide us with evidence to support the theory of evolution.
Evidence of the theory of evolution
- Paleontology
- Comparative anatomy
- Comparative embryology
- Biogeography
- Molecular biology and genetics
Evidence from Paleontology
Paleontology : is the study of fossils
- Fossils are the remains of ancient life forms preserved in the rocks, e.g bone fragments etc..
How do scientists tell the age of a fossils ?
"There Two ways scientists can tell the age of fossils"
Using Relative dating and radiometric dating
- Relative dating: In relative dating scientists try and figure out the age of a fossil by comparing the age of another fossil or geographical event, such as volcanic eruption.
- Radiometric dating: In radiometric scientists attempt to find out the age of a fossil by finfing out how long ago a particular fossil was formed.
Fossils provide the only direct evidence of the history of evolution
Evidence from Comparative Anatomy/Modification by descent
Scientists used comparative anatomy to determine relationships between species
Organisms with similar structure, they argue, must have acquired these traits from a common ancestor
For example lets look at the forelimp structure of certain vertebrates like (mole, bat, horse, seal, monkey) they all have a basic struture plan suggesting that they may arose from a common ancestor
Homologous struture
- The structure which have the same basic plan, but have different functions e.g Human forelimp and cat forelimop
Analogous struture
- The structure peforms the same function but is different from other strutures e.g butterfly and bird
Evidence from Biogeography
Biogeography is the study of the distribution of life forms over geographical areas.
Other evidence in support of evolution comes from biogeography, this is what first suggested to charles darwin that species evolve from a common ancestor.
Evidence from Molecular Biology and Genetics
Scientists argue that organisms are closely related if they have...
- Identical DNA Struture
- Similar Sequence of Genes
- Similar Portions of DNA with No Function
- Identical Protein Synthesis and Similar Protein
- Similar Respiratory Pathways
Evidence from Comparative Embryology
By comparing the structure of an embryo in its early development stage , scientists figured that most vertebrates embryo look alike in their early development stage this could be because they arose from a common ancestor.
For Example the embryo, of a fish , chicken, pig and human all look alike and sometimes are even hard to differeniate.
Lamarckism
Lamarckism is the idea that organisms can pass on their characteristics, that they have acquired during their lifetime to thier offsprings.
It was named after the biologist Jean-Baptiste de Lamarck (1744-1829).
Jean-Baptiste Lamarck explained evolution (On how organisms undergone change) using the following two ‘laws’.
1) The law of inheritance of modified/acquired characteristics:
- For this Law Lamarck believes that change in organisms happpened because they deliberately wanted to change to better adopte to the enviroment.
Example : The long neck of the giraffe came about because it wanted to feed on the tree tops, to avoid competition.
2) Law of use and disuse:
- For this Law Lamarck believes that when an organisms uses a structure or an organ more regular, it becomes better developed or enlarged overtime. If an organisms does not use a structure or organ frequently, it becomes less developed or reduced in size and may disappear altogther.
Why Lamarck's theory is rejected by most biologists
- Biologists say that Organisms evolved, not because they wanted too, but because change took place randomly in response to the enviroment
- Biologists say that there just not enough evidence to prove/support Lamarck's idea that changes brought about by adoptation to the environment are inherited from parent to offspring
Darwinism
Darwinism is a theory that explains the evolution of new species through natural selection.
It was named after Charles Darwin (1809-1882)
Charles Darwin theory of evolution is based on 5 main observations and assumptions
- Variation:There is a great deal of variation among members of the same species.
- Offspring:Species produce a large number of offspring but not all survive.
- Competition:Organisms compete for limited resource, such as food and teritory.
- Genetics:Organisms pass genetic traits on to their offspring.
- Natural Selection:Those organisms with the most favourable characteristics are more likely to survive and reproduce.
Darwin's Theory of Evolution by Natural Selection

- Both plant and animals generally produce a large number of offspring.
- The offsprings produced of the same species show a great deal of variation.
- The offsprings produced compete with each other for avaliable resources.
- Only those with favourable characteristics will survive and reproduce.
- Darwinism called this Natural selection
- Since the individuals with favourable characteristics survive, they will continue to reproduce offsprings that are have favourable characteristics.
- Organisms which do not have favourable characteristics, will not cope with the environment and therefore die.
Difference between Lamarck's and Darwin's Theories
Lamarck's Theory
- Variation in offspring brought by individuals in the population changing
- Change is brought about because individuals in the population wanted to change
- Change brought about by individuals in the population adapting to the environmnet
- Individuals in the population change
- Changes brought about by adaptation to the environmnet are inherited from parent to offspring
Darwin's Theory
- Offspring showed variation from the moment of their production
- Change as a result of environmental factors working randomly on the population
- Change brought by nature selecting those that are best suited to environmnet to survive
- The population as a whole changes
- Characteristics are passed on from generation to generation because they enable the inidividuals to survive in the environment.
Punctuated Equilibrium
According to this theory, most species do not undergo any change for long period of time. Then, suddenly, the species undergo rapid change over a short period of geological time, resulting in new species.
Theory of punctuated equilibrium for the tiger stripes
- Millions of years ago, there were lot of tigers without black strips.
- Then suddently, a mutation occurred in a few of the animals, causing some of the tigers to be born with stripes
- Tigers with stripes were able to camouflage themselves from prey using tall grasses and trees.
- Tigers without stripes were out-competed by tigers with stripes.
- Over only a few generations, the whole population was born striped.
Gradualism
- Gradualism is selection and variation that happens more gradually.
Theory of gradualism appiled for the stripes of tigers
- At first, the entire population of tigers was without stripes.
- Some tigers developed marks on their fur, as a result of mutation.
- Marked tigers were able to camouflage themselves better than the stripes less tigers, so few tigers without stripes survived.
- At the same time, the marks gradually became clear stripes.
- Eventually, the entire population of tigers became striped.
Artificial Selection
Artificial selection is a form of selection which humans actively choose which traits should be passed onto offsprings to have desirable characteristics.
Differences Between Artificial Selection and Natural Selection
Definition
- Natural Selection: Natural selection is the process whereby organisms better adapted to their environment tend to survive and produce more offspring.
- Artificial Selection: Artificial selection refers to the process by which animals and plants are chosen by the breeder to produce desirable and inheritable characters in the successive generations.
Selection
- Natural Selection: Natural selection is a nature-made selection process.
- Artificial Selection: Artificial selection is a man-made selection process.
Significance
- Natural Selection: Natural selection produces a huge biological diversity.
- Artificial Selection: Artificial selection produces organisms with selected traits.
Occurs in
- Natural Selection: Natural selection occurs in natural populations.
- Artificial Selection: Artificial selection mainly occurs in domestic populations.
Importance
- Natural Selection: Natural selection only allows favorable characters to be inherited over the successive generations.
- Artificial Selection: Artificial selection allows only selected traits to be inherited over successive generations.
Speed
- Natural Selection: Natural selection is a slow process.
- Artificial Selection: Artificial selection is a rapid process.
Effect on Evolution
- Natural Selection: Natural selection facilitates evolution through generating biological diversity.
- Artificial Selection: Artificial selection does not facilitate evolution.
Speciation
Speciation : means the formation of new species.
Types of Speciation
- Allopatric speciation
- Sympatric speciation

Allopatric speciation
- New species are formed who a population of the same species becomes separated by a geographical barrier e.g contient split, mountain or river.
- Each sub-population then develops into a new species.
Sympatric speciation
- New species are formed without the presence of a geographic barrier to separate the population.
- Instead the population may develop reproductive barrier which prevents them from interbreeding, resulting in separate species.
Speciation by Geographic isolation (Allopatric Speciation)
- A population of a particular species may become split...
- by a geographical barrier, e.g. a river.
- As a result, the two parts of the population cannot interbreed
- There is no gene flow between the two populations.
- Natural selection occurs independently in each population.
- This is due to different environmental conditions.
- As a result, the two populations become genotypically and phenotypically different over a period of time.
- Even if the two populations mixed at a later time, they will not be able to interbreed again.
- We say that one or both parts of the population have become a new species = speciation.
Mechanisms of Reproductive Isolation
Reproductive isolation or reproductive isolating barrier are factors that prevent two species from producing fertile offspring.
Habitat Isolation
- When two closely related species live in different habitats.
Temporal Isolation
- When two species breed during different times (seasons) of the year.
Species-specific Courtship Behaviour
- When two species develop develop new ways of attracting mates that might not attract the other mates.
Adaptation to Different Pollinating Agents
- Differences in structure can prevent successful mating.
Prevention of Fertilisation
- In some closely-related species fertilization of the different species is prevented by the different species having different copulatory organs.
Hybrid Infertility
- Some closely-related species may mate and produce viable offspring.
Evolution in Present Time
Scientists have used the way in which insects have developed resistance to insecticides, and the way in which bacteria have developed resistance to antibiotics as examples of evolution by natural selection in present times.
The developement of Resistance to insecticides by insects
- There is great deal of variation amongst mosquitoes.
- Insecticides were created to kill mosquitoes.
- Some mosquitoes became resistent to the insecticides.
- More mosquites resistent to the insecticides lived and reproduced and produced fertile offsprings that are also resistance.
- While those without resistance died.
- Thats how the population of resistent mosquites evolved.
Our Place in the Animal Kingdom
There are Five kingdoms one of which is the Kingdom Animalia or commonly called the Animal Kingdom
Animalia/Animal Kingdom
There two large groups within the Animal kingdom
- Invertebrates (Animals without bones)
- Vertebrates (Animals with bones)
Vertebrates
Vertebrates can be sub-divided into the following classes
- Class Pisces (fishes)
- Class Amphibia (frogs)
- Class Aves (birds)
- Class Reptilia (snakes and lizards)
- Class Mammalia (rabbits, monkeys, humans) *
Modern Humans are classified as Primates.
The scientific name for Modern Human is Homo sapiens.
Early Humans are often called ape men, since they showed some characteristics of apes and some characteristics of humans.
Order Primates
There two sub-orders that exist with the Order Primates
- Anthropoidea (Monkeys, apes and humans).
- Prosimii
Anthropoidea
Three families exits with the Anthropoidea
- Hylobatidae : Gibbons
- Pongidae : orangutans, gorillas and chimpanzees
- Hominidae : Humans
Hominid and Hominin
Note : The family pongidae doesn't exist anymore since scientist believe that African Apes are closely related to Humans.
- Now the African Aps fall under the Hominidae family.
Hominid: All modern and extinct great apes. Gorillas, chimps, orangs and humans and their immediate ancestors.
Homini:Any species of early human that is more closely related to humans than chimpanzees, including modern humans themselves.
Similarities betweeen African Apes and Humans
The Upper Limbs
- Opposable Thumbs
The Brain
- Large brain compares to their bidy masses
Vision
- Cones and rods
- Binocular vision
Number of offsprings produced
- Fewer offsprings than other mammals
Upright posture
- Ability to sit upright
African Apes
- Quadrupedal - knuckle-walkers
- Foramen magnum (opening for spinal cord) at back of skull
- C-shaped vertebral column
- Arms longer and stronger than legs
- Knee joints smaller and weaker
- Opposable (grasping) big toe with power grip
- Flat feet
- Long and narrow pelvis
- Smaller, less developed brain
- Large, prominent canines
- Thin tooth enamel
- Large, prominent jawbone with no chin (prognathism)
- Wider, sloping face
- Narrow, rectangular palate
- Prominent cranial and brow ridges
Humans
- Bipedal - walk upright on two legs
- Foramen magnum closer to front of skull (central under skull)
- S-shaped vertebral column
- Arms shorter and weaker than legs
- Knee joints larger and stronger
- Non-opposable (forward-thrusting) big toe in line with other toes
- Curved foot arch
- Short and wide pelvis
- Large, developed brain
- Smaller canines; the same size as other teeth
- Thick tooth enamel
- Rounded jaw with developed chin (reduced prognathism)
- Narrow, flat face
- Wider, more curved palate
- Reduced cranial and brow ridges
Evidence of common ancestors for living hominids (including humans)
- The evolutionary theory does not state that humans evolved from the chimpanzee or the gorilla, but it proposes that they share a common ancestor.
- Scientists are searching for a common ancestor of all living hominids.
- The big question scientists have to answer is whether the common ancestor was ape-like or human-like.
- Remains of earlier hominids are very rare.
Three main lines of evidence
- Fossil evidence
- Genetic evidence
- Cultural evidence
Fossil evidence
- Paleontologists study fossils to provide more information on the structure, movement, lifestyle and environment of a particular species.
- Certain features of hominid fossils indicate how changes occurred over time.
- Hominid fossils are rarely complete and consist mainly of fragments.
- Most hominid fossils are teeth, jaw bones or skull fragments.
- The remains of feet, hands, pelvic bones or vertebral columns are scarce.
- Long bones e.g. femurs are more commonly found.
- In the search for a common ancestor for hominids, palaeontologists look particularly at the following features of hominid fossils:
- bipedalism
- brain size
- dentition (teeth) prognathism
- palate shape
- cranial
- brow ridges
- Bip
Bipedalism
- The greatest observable difference between apes and humans lies in the difference in posture and method of locomotion.
- Apes are four-footed (quadrupedal) with gorillas and chimpanzees demonstrating a particular manner of walking, i.e. knuckle-walking.
- Humans, however, are bipedal and walk upright.
Advantages of bipedalism
The human vertebral column is S-shaped for flexibility and shock absorption. The vertebral column of apes is C-shaped.
Brain size
- Hominid fossils indicate that the size of the cranium increased in most fossils over time.
- We may conclude that, in general, the size of the brain (brain capacity) increased over time.
- The cranium of apes is small and elongated and contains a small, less developed brain.
- Chimpanzee brains have an average size of approximately 395 cm3.
- Humans have a more rounded skull with an enlarged cranium which contains a large, highly developed brain.
- The average size of the human brain is approximately 1 400 cm3.
- The more complex human brain gave rise to:
- well developed hand-eye coordination (to make and use tools)
- The capacity for language
- The use of fire
Dentition (teeth)
- The size of teeth decreased with the course of evolution.
- Apes have large prominent canines that are larger than other teeth.
- In apes, there is a large gap (diastema) between the incisors and the canines. It provides space for the protruding canines on the opposite jaw so that the mouth can close.
- The human canines are the same size as the other teeth.
- The diastema disappeared completely over time.
- The tooth enamel became thicker over time. In apes it is very thin, in hominins it is thicker and in humans it is very thick.
Prognathism
- Apes have large, protruding jaws (snout or muzzle) without a chin.
- Humans have a narrow, flat face with rounded jaws and a protruding chin.
Genetic evidence
Scientists states that organisms are closely related and likely to have a common recent ancestor if they have.
- Identical DNA structure
- Similar sequence of gene
- Similar portions of DNA with no function
Cultural evidence: tools
- The production and use of tools and other cultural practices like fire-making, burial rites, art and hunting techniques are suggested as further evidence of common ancestors for living hominids.
- The development of speech and language is another cultural change that distinguishes modern humans from primates.
Major phases in the hominid evolution (from 6 mya to present)
- The main hominin genera within the hominid group are the following:
- Ardipithecus
- Australopithecus
- Homo
- The timeline of human evolution probably began 6 - 7 million years ago.
Ardipithecus
- Ardipithecus ramidus was an early hominin that lived approximately 5,8 - 4,4 million years ago.
- About 17 Ardipithecus fossils were found in the Afar valley of Ethiopia in 1993.
- These beings show ape-like as well as australopithecine characteristics, indicating that Ardipithecus could be a transitional form between the apes and Australopithecus.
General characteristics of Ardipithecus
- Probably bipedal.
- Foramen magnum positioned centrally below skull, but more to the front than in apes.
- Pelvis is wider at the top, and narrow and long at the bottom as in apes.
- Long arms (almost as long as the legs) for climbing trees.
- Opposable, grasping big toe.
- Small brain capacity of approximately 300 - 350 cm3.
- Ape-like teeth, but smaller canines and molars; a diastema is present
- Protruding jaw (snout/muzzle) without a chin.
- Sloped face.
- Palate is narrow and rectangular.
- Small brow ridges.
Australopithecus
- Australopithecines are regarded as the first bipedal primates.
- They have both ape-like and human-like characteristics and they are sometimes called ape-men.
- The genus name Australopithecus literally means 'southern ape'.
- It is estimated that australopithecines lived in Africa between 4,5 and 1,4 million years ago.
- During this time the African forests increasingly made way for sparse woodlands, grasslands and savannas.
- Australopithecus fossils were found mainly in Eastern and Southern Africa.
General characteristics of Australopithecus
- Bipedalism and upright walking.
- Foramen magnum is positioned centrally below the skull. Pelvis is short and wide.
- Long arms for tree climbing.
- Fingers long and curved; non-opposable big toe.
- Brain capacity larger than that of the apes, approximately 380 - 500 cm3.
- Teeth more human-like; smaller canines than apes, but larger than humans; small diastema.
- Protruding jaw without a chin.
- Sloping face (less sloping than in apes).
- U-shaped palate.
- Large brow ridges.
- The 3,8 million year old footprints discovered in Laetoli,Tanzania are one of the oldest fossils indicating evidence of bipedalism of Australopithecus.
- Australopithecus probably developed simultaneously with the Homo genus and is therefore not regarded as a human ancestor.
- Various Australopithecus fossils of different species have already been found in Africa
Five well-known australopithecines
- Taung child
- Mrs Ples
- Lucy
- Little Foot
- Australopithecus sediba
Taung child (Australopithecus africanus)
In 1924 the fossil skull of a hominin was found by Professor Raymond Dart at Taung, northwest of Kimberley.
- It was the skull of a child of about 3 - 4 years old.
- The skull had human as well as ape-like characteristics: a small brain capacity (340 cm3) similar to apes human-like teeth foramen magnum in a more central position, indicating bipedalism
- The Taung skull is classified under Australopithecus africanus, who lived about 3 - 2 million years ago.
Mrs Ples (Australopithecus africanus)
In 1947 a complete adult skull and various bones were found by Dr Robert Broom in the Sterkfontein Caves in South Africa.
- This skull was about 2 - 3 million years old and was also classified as Australopithecus africanus.
- The brain capacity is estimated to be similar to that of a chimpanzee.
- From the position of the foramen magnum it could be deduced that Mrs Ples was bipedal and walked upright.
- The jaws indicated that there were no protruding canines, and the dentition indicated a diet of mainly plant material with little meat.
Lucy (Australopithecus afarensis)
Lucy is a fossilised female skeleton found by Donald Johanson at Hadar in the Afar valley, Ethiopia in 1974.
- The skeleton dates back 3,5 million years.
- The shape of the pelvis indicated that Lucy was female.
- The skeleton was about 1 m long and showed evidence of bipedalism.
- The face had ape-like characteristics, i.e. a low forehead, flat nose, protruding lower jaw and large canines.
- The arms were long and the legs short.
- The brain capacity of 400 cm3 was similar to that of apes.
Little Foot (Australopithecus species)
In 1994 the ankle and foot bones of an australopithecine fossil was discovered in the Sterkfontein Caves by the palaeoanthropologist Dr Ron Clarke.
- The fossil was named Little Foot.
- The rest of the skeleton was found in 1997.
- The excavation of the complete skeleton from the rock is still in progress.
- It has already been determined that Little Foot was bipedal because of the position of the foramen magnum.
- The arms are short and the bones of the hand are very similar to those of the modern human, with short palms and fingers.
- The species to which Little Foot belongs will only be determined when the entire skeleton has been removed.
Australopithecus sediba (2 - 1,7 mya)
- In 2008 two fossils, those of a young woman and boy, were discovered in the Cradle of Humankind in the Malapa area by Professor Lee Berger and his 9-year-old son, Matthew.
- These fossils represent a new species, Australopithecus sediba, which was announced to the world in April 2010.
- The fossils are between 1,78 and 1,95 million years old and the most complete early hominins discovered so far.
- Australopithecus sediba is considered a transitional fossil between the older Australopithecus africanus and the first Homo species, and possibly gave rise to the origin of modern humans.
- Australopithecus sediba has a small brain and large brow ridges in comparison to modern humans, but the shape indicates a more advanced brain than that of other australopithecines.
- Early australopithecines were able to walk upright, but could not run fast or walk for long distances.
- Similarly, Australopithecus sediba had long arms and short hands adapted for tree climbing, while the pelvis was similar to that of early Homo species and adapted for walking long distances.
- Professor Berger and his colleagues believe that Australopithecus sediba could probably be the ancestor of modern humans.
HOMO
- The genus Homo appeared in Africa about 2,2 million years ago.
General characteristics of Homo
- Bipedalism with upright walking.
- Central foramen magnum at the base of the skull, directly above the vertebral column.
- Pelvis is short and wide.
- Legs are long in relation to arms; longer femurs for greater stride.
- Short, straight toes; non-opposable big toe; enlarged heel bone; opposable thumb.
- Larger brain with a brain capacity of approximately 600 - 1 400 cm3.
- Smaller teeth (no protruding canines), no diastema.
- Jaws more rounded with a prominent chin in Homo sapiens; older species have protruding jaws.
- Flat face.
- Wide, curved palate.
- No brow ridges in Homo sapiens; older species have large brow ridges.
Homo species
- Homo habilis
- Homo erectus
- Homo neanderthalensis
- Homo sapiens
Homo habilis (handy man)
Homo habilis lived in Africa, together with other Australopithecus species, about 2,2 - 1,6 million years ago.
- Australopithecus africanus probably gave rise to Homo habilis.
- In 1960 a Homo habilis fossil was discovered in Tanzania.
- The body of Homo habilis was smaller than that of Australopithecus and it was ape-like.
- They also had a larger brain (640 cm3) than Australopithecus, which meant they had better skills in using their hands to make tools.
- Homo habilis was the first group that used stone tools.
Homo erectus
- Homo erectus is a species that is closer to modern humans than to Australopithecus.
- Homo erectus literally means 'upright man' and they lived 1,8 - 0,3 million years ago.
- They were probably the first hominins to migrate from Africa to Europe and Asia.
- The most complete Homo erectus fossil is 1,5 million years old and was found Differences between genera Australopithecus and Homo near Lake Turkana in Kenya. It is known as the Turkana boy.
- Homo erectus had large bodies, similar to those of modern humans.
- Their skulls were thick with low, prominent foreheads, heavy brow ridges and no chin.
- Both jaws were relatively massive with large teeth.
- Their brain capacity was about 1 000 cm3.
- Homo erectus made and used stone and bone tools.
- They were successful hunters and the first species that learnt to use fire
Homo neanderthalens
- The Neanderthals were a group of people that lived between approximately 230 000 and 30 000 years ago in Europe and Western Asia.
- The first fossil was discovered in 1856 in the Neander Valley in Germany.
- Their skulls were long and flat, with a low forehead, broad nose and a prominent brow ridge above the eyes.
- Although their brains were larger than Homo sapiens, language was not well developed and their technological development was limited.
- They were hunters, wore clothes made from animal skins, built shelters in caves and used fire.
- They buried their dead, which is an indication of some form of 'spiritual life' or advanced culture.
Homo sapiens
- This group is considered to be the direct ancestors of modern humans.
- Presumably, Homo sapiens appeared about 200 000 years ago.
- It is claimed that the appearance of Homo sapiens resulted in the disappearance of the Neanderthals.
- Homo sapiens developed better skills and had more advanced technology. Therefore modern humans are not directly related to Homo neanderthalensis.
- Homo sapiens used tools made from bone as well as stone, which included spears, arrows, bows and hooks for fishing.
- Their clothes were made mainly from leather and plant material.
- They lived in tents and formed communities.
- As hunters they followed the annual animal migrations in the summer.
- They developed agriculture and cultivated the land.
- They wore jewellery and decorated their bodies with paint.
- They developed rituals that were linked to hunting, births and deaths
- Like the Neanderthals, they buried their dead which indicates a development of advanced culture and spiritual rituals.
'OUT OF AFRICA' Hypothesis
- According to the 'Out of Africa' hypothesis, Homo sapiens originated in Africa about 200 000 years ago and migrated relatively recently (50 000 ya) to the rest of the world.
- These early Homo sapiens had a higher level of technological skills, were better adapted to their new environment and out-competed other Homo species.
- This resulted in the more successful Homo sapiens replacing Homo erectus in Asia and Indonesia and Homo neanderthalensis in Europe.
Evidence of african origins for all modern humans
The following evidences support this hypothesis:
- Genetic links
- Fossils and artefacts of hominins found in Africa
Genetic links as evidence for the ‘Out of Africa’ hypothesis
- Scientists increasingly make use of genetic studies where sections of DNA are used to determine ancestry.
Different types of types of DNA are used:
- Chromosomal DNA (excluding Y-chromosomes)
- Mitochondrial DNA (mtDNA)
- Y-chromosome DNA
Arguments against Evolution
People who do not believe in evolution put forward four main arguments aginst evolution. They say that:
- The Earth is only about 6 000 years old not 4.5 billion years old as claimed by those who believe in evolution.
- The probability of forming a single molecule by chance is incredibly small.
- When things are left on their own, they get more disorderly or less organized.
- The fossil record has too many gaps in it to be accepted as proof of evolution
Some Alternate Theories of Diversity
- The believe that all living forms have been created by some Supreme Being. So the organism that have been created have not changed since their creation.
- Different forms of life were designed to functionin particular settings.
- Cells are too highly organised to have arisen on their own.
- The differences between different kinds of organisms are too complex for them to have evolved from a common ancestor
- Taking whats writtern in religious books to be literally true.
- Theistic evolutionists believe in God and Evolution, they say that natural selection is simply the plans of gods.
Creationism
Intelligent Design
Theory is based on the following ideas:
Literalism
Theistic Evolution
The atmosphere and climate change
- Climate refers to the long-term weather conditions of an area.
- The atmosphere is made up of nitrogen, oxygen and other gases, which include the greenhouse gases such as carbon dioxide and methane.
- The greenhouse effect is important in keeping the Earth warm so that it can sustain life. However, an increase in the concentration of greenhouse gases leads to the ‘enhanced greenhouse effect’. As a result, there may be a significant rise in the average temperature of the surface of the Earth over a period of time. This is known as ‘global warming’
Increased concentration of carbon dioxide in the atmosphere is due mainly to:
- Burning of fossil fuels (for electricity, to power vehicles and for industrial processes): Combustion of carbon-rich fuels such as coal or plants (w ood) releases carbon that was stored in them, as carbon dioxide.
- Deforestation : Cutting down trees and removing vegetation from the land decreases the amount of carbon dioxide taken up by plants during photosynthesis. This increases the amount of carbon dioxide available in the atmosphere.
Increased concentration of the methane in the atmosphere is due mainly to:
- The increased number of landfills: decaying organic matter in waterlogged soils such as landfills releases methane.
- The increased number of livestock: ruminants such as cows release methane gas through their digestive tracts.
- Mining of coal.
Increased temperatures may lead to:
- More evaporation of water which can lead to increased precipitation which eventually increases the potential for flooding.
- Rising sea levels caused by melting ice in the glaciers which can eventually increase the potential for flooding.
- Increased wildfires that increase the chances of soil erosion and eventually desertification.
- Increased loss of biodiversity, as species are unable to cope with rapidly rising temperatures, eventually leading to desertification.
- Increased droughts in some areas leading to desertification and food insecurity.
Carbon footprint
This is a measure of the total amount of carbon dioxide emissions of an individual, a defined population or a company per year.
Strategies to reduce the carbon footprint include the following:
- Reuse and recycle: less fossil fuels burnt in the production of some of the material.
- Drive less: by using public transport, walking, bicycles.
- Reduce the need for heating: insulating walls and building energy efficient homes.
- Carbon offsetting: by using alternative energy (solar and wind) and reforestation to act as a carbon reservoir.
- Technological developments: decrease the amount of energy needed for production/decreasing the dependency on carbon emitting fuels.
Destruction of the ozone layer
Ozone is a greenhouse gas that is found at low concentrations 15 – 50 km above the Earth’s surface.
- There will be a significant increase in the number of skin cancer cases.
- Ultraviolet rays reaching the Earth’s surface may cause permanent damage to our eyes.
If the measures to reduce the destruction of ozone layer fail:
Availability of water
The availability of water may be influenced by the following factors:
Construction of Dams
- The construction of additional dams plays a major role in increasing the quantity of water stored and made available for later use by people and in agriculture.
Destruction of wetlands
- Wetlands should not be destroyed because they influence both the availability and quality of water.
Water wastage
- A large amount of water used for irrigation is lost due to poor farming practices. Open drain irrigation leads to loss of water by evaporation. The use of water for irrigation further up a river decreases the availability of water for other users lower down the river.
- Availability is also affected by wastage of water through leaking taps and toilets and faulty pipelines.
- Wastage of water can be reduced by reducing the pressure in the pipes, by educating people to use water wisely and by maintaining all plumbing in good condition.
Cost of water
- The cost of water is influenced by costs involved in increasing the availability and quality of water.
- The cost per kilolitre (kl) of water increases with the increased use of water. This is meant to discourage over-use of water, thus allowing for its sustained use.
- A certain amount of water is available free to all citizens to ensure that water is available to the poorest.
Poor farming practices
- Contamination of water sources by fertilizers and pesticides has decreased the amount of clean water available, thus increasing the costs involved in purification.
- Over-grazing leads to soil erosion. On land that is eroded, water runs off rapidly rather than soaking into the ground, and is thus wasted.
Droughts and floods
- During periods of drought, water availability decreases. Water used from dams during the drought periods cannot be easily replaced.
- Natural vegetation can hold back water from floods. If the natural vegetation is removed, flood waters are lost. Boreholes and their effect on aquifers
- Boreholes have been used to increase water availability in areas that do not have direct access to other sources of water.
- Constant use of boreholes eventually leads to the drying up of aquifers (the source of borehole water) thus decreasing water availability in the future.
Water recycling
- The availability of water can be increased if existing water is used for more than one purpose. For example, some water used in the household can be used for the garden. Sewage water can be treated and used again. Exotic plantations and the depletion of the water table
- Some exotic plants use a large quantity of water from the ground. As a result, this decreases the level of the water table, making less water available to other vegetation in the area.
Quality of water
The quality of water may be influenced by the following factors:
- Water used for agriculture may contain pesticides, herbicides and fertilizers which pollute the water in rivers, dams and lakes, causing eutrophication. The added nutrients lead to an increase in algal growth (algal bloom). These algae over-use and thus deplete the oxygen in the water, thus reducing the potential for life in such water.
- Thermal pollution refers to the heating of water caused by the use of water for cooling in power-stations and industries.
- The quality of water is affected because heated water has a lower oxygen content, making it difficult to support life. Pollution of water through domestic, agricultural and industrial use
- After water is used for domestic purposes it may contain detergents (such as from washing) and pathogenic bacteria (such as in sewage). This polluted water has to be treated before it can be used again.
- After water is used for industrial purposes it may contain many heavy metals, oil, heat and fertilizers. This adversely affects the quality of the water and all life that depends on it.
- Fertilisers and pesticides may run off into rivers, ponds and dams and pollute the water. Mining
- Water returned to the environment from mines is generally acidic and toxic. This water is hot and thus also contributes to thermal pollution.
- Alien invasive water plants block the waterways, reducing light to other aquatic plants. These plants eventually die and decompose. Bacteria that decompose these plants eventually deplete the oxygen supply in the water.
- The quality of water is improved through purification methods. Undrinkable water can be made drinkable.
Eutrophication and algal bloom
Thermal pollution
Alien Plants
Water purification
Food security
Food security refers to the access, by all people at all times, to adequate, safe and nutritious food for a healthy and productive life. Food security may be influenced by the following factors:
Exponential growth of the human population
- The world’s population is growing at an exponential rate (very rapidly) and as a result some countries cannot produce enough food to feed their growing population. Food production needs to increase as rapidly as the world population; otherwise many countries will experience food insecurity.
Droughts and floods
- Climate change has led to more frequent and severe droughts and floods. Droughts result in crop losses and livestock death which reduce the food available in an area. Floods cause extensive damage in a short period of time and decrease the amount of farmland available to grow crops. People also usually lose their homes, possessions and economic security during floods, further impacting on food security
Poor farming practices – monoculture, pest control, loss of topsoil and the need for fertilizers
- Monoculture is the growing of one type of crop over large areas of land year after year. Monoculture depletes nutrients and water supplies and therefore impacts negatively on the quality of the topsoil.
- Pest control involves the use of pesticides (chemicals) to kill pests that compete with humans for food. Pesticides may kill or get into the tissues of healthy plants. This may reduce crop production and, since pesticides are expensive, increase the cost of food and thus reduce access to poor consumers. Many farmers now use biological control, which uses a natural predator/parasite to get rid of the pest instead of using expensive pesticides.
- Topsoil is the top 1.5 metres of soil that contain the nutrients that plants require for growth. The tilling of the soil between plantings and heavy rainfall cause much of the topsoil to be lost, leading to the loss of valuable nutrients over time, reducing crop yields.
- The use of fertilizers, both inorganic (chemical) and organic (compost and manure) can increase the nutrients in the soil and keep soil fertile. This replaces nutrients in the soil that are lost when crop plants absorb them. Fertilizers can be expensive, contributing to the high cost of food, thus reducing access to poor consumers.
Alien plants and reduction of agricultural land
- Alien plants deplete the topsoil of water and nutrients. These alien plants out-compete indigenous plants because they have no natural predators, grow rapidly and invade land that could be used to grow crops.
The loss of wild varieties and the impact on gene pools
- Crop plants have replaced wild varieties. The preservation of wild varieties is important because, if changing environmental conditions destroy the present crop plants, then wild varieties could be used as alternative sources of food. If wild varieties are wiped out, it will reduce the genetic diversity and thus the gene pool.
Genetically engineered food
- Genetically engineered food is produced from genetically modified organisms (GMOs). Genetic engineering involves the inserting of a gene (with a desired characteristic) from one organism into another organism to increase the yield. For example, a gene for drought resistance could be inserted into a crop plant that grows in areas where water is scarce.
Food wastage
- Wastage could occur during the storage, production and processing of food. Wastage includes food thrown away and food not eaten. Wastage increases the prices of food to consumers and could reduce food security in a country.
Loss of biodiversity
Biodiversity refers to the variety of plant and animal species on Earth.
Factors that reduce our biodiversity
Farming methods
- Monoculture : Monoculture is the growing of one type of crop over large areas of land year after year. Monoculture replaces indigenous plants and reduces biodiversity. Insects that specialise in feeding on one type of crop spread rapidly because there are no natural enemies or barriers to stop them. This means the farmer needs to use more pesticides to kill them. Intensive use of agrochemicals such as fertilisers and pesticides often end up in rivers, streams and groundwater, poisoning species in the area and causing eutrophication. This results in a large loss of biodiversity. Overgrazing: It occurs when livestock such as sheep or cattle are kept in an area for too long; the vegetation is grazed to a point where it will not grow back. It causes soil erosion by removing the plants that bind the soil together with their roots. Topsoil is lost during rainstorms. This can lead to the extensive destruction of land through desertification which results in loss of biodiversity. Sometimes overgrazed land becomes subject to alien plant invaders which destroy habitats by taking over the land.
Golf Estates
Developments such as golf estates are a form of monoculture that requires large amounts of water, pesticides and fertilisers which may runoff and poison aquatic ecosystems. Housing associated with golf developments replaces large areas of natural vegetation.
Mining
- Mining alters the environment and can negatively affect the biodiversity in an area. Pollutants in the form of dust and smoke may be released into the air while vegetation is removed and replaced with rock and waste dumps. Underground water may be poisoned because of sulphates and heavy metals released into them.
- Urbanisation The growth of large cities (urbanisation) also negatively impacts on biodiversity. Surfaces are covered with concrete, and natural habitats are destroyed to build houses and businesses. Habitat fragmentation causes the loss of biodiversity, as natural plants are replaced by exotic trees and plants.
Deforestation
- Deforestation is the permanent destruction of indigenous forest and woodland areas. Deforestation is caused by human activities such as agriculture, logging, and using trees as firewood. Deforestation leads to the destruction of the habitats of other organisms, like frogs and insects, and this leads to the loss of biodiversity.
Loss of wetlands and grasslands
- Grasslands and wetlands have unique plant and wildlife and provide many ecological services to humans. Destruction of these habitats will lead to the loss of species.
Poaching
- Poaching refers to the illegal hunting of animals, either for food or because certain body parts can be sold for money. ‘Poaching’ may also be applied to plants that are removed and sold for profit e.g. medicinal plants. Some wild animals are hunted for food (‘bush meat’) and are on the verge of extinction. Elephants are poached for their tusks to make carvings and jewellery and rhinos are hunted for their horns which are used in the Far East for medicinal reasons.
- Alien plant invasions These plants are species that have been introduced into an area and which compete with the natural plants in the area. They can outcompete indigenous plants, thus reducing the biodiversity.
Ways in which our biodiversity can be maintained
Control of alien plant invasions
Alien invasive species may be controlled by mechanical, chemical and biological methods. Mechanical methods involve chopping down plants or physically removing them by hand and is very time consuming. Chemical control involves spraying herbicides onto the plants; this can pollute the environment and is expensive. Biological methods involve introducing a natural enemy from the alien plant’s environment and allowing it to reproduce and feed on the invasive plant.
Sustainable use of the environment
Sustainable use of the environment means using resources without harming the ability of future generations to use that resource. Substances from indigenous plants such as the African potato, Hoodia, rooibos and Devil’s claw all have economic and medicinal value. These indigenous plants can be used sustainably by encouraging traditional healers to grow their own plants and through improving education of the women who generally gather the plants in the wild. Encouraging traditional healers to be part of formal medical programmes would encourage training to be ongoing and help establish sustainable use of medicinal plants. Legislation should be passed to limit the numbers of plants that can be harvested at one time and seeds of medicinal plants could be collected and distributed to increase plant numbers.