Topic 1 :Nucleic Acid

Image not found Location of DNA in the cell

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 DNA

DNA 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.

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

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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.

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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
Eukaryotic cell: a cell that possesses a membranebound nucleus and membranebound organelles.
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.

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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
Image not found The illustration of the DNA replication process.

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

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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)

  • Forms the ribosomes, which are found free in the cytoplasm of the cell and are attached to the outside of the endoplasmic reticulum. Ribosomes are the site of protein synthesis.
  • Transfer RNA (tRNA)

  • It picks up amino acids in the cytoplasm and brings them to the ribosomes where they are joined together to form a protein
  • 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


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    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
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    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.
    Translation (takes place in the cytoplasm on 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.
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    Meiosis

    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.
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    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

    Interphase 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.
    Image not found Prophase 1
    • 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.
    Image not found Metaphase 1
    • 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.
    Image not found Anaphase 1
    • The spindle fibres shorten and pull each chromosome of each chromosome pair to opposite poles of the cell.
    Image not found Telophase 1
    • 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.
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    Meiosis II

    • Prophase 2
    • Metaphase 2
    • Anaphase 2
    • Telophase 2
    Image not found Prophase 2
    • Each cell formed during meiosis I now divides again.
    • A spindle forms in each of the new cells
    Metaphase 2
    • Individual chromosomes line up at the equator of each cell, with the centromeres attached to the spindle fibres.
    Anaphase 2
    • The spindle fibres start to contract.
    • The centromeres split and daughter chromosomes/ chromatids are pulled to the opposite poles of each cell.
    Telophase 2
    • 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

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    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.

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    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

    Image not found Random assortment

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

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    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.
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    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

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    Charateristics

    • small eyes
    • stocky body
    • distinct facial
    • big forehead
    Reproduction in vertebrates

    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.
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    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.

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    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
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    Vivipary

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

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

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    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.

    Human reproduction

    Structure of the male reproductive system

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

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    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
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    Fertilisation and Development to Blastocyst Stage

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    • 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.
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    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

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    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.

    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

      Condom:

    • 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.
    Genetics and inheritance

    Key concepts

    The following are very important terminolgies to understand for for Genetics

    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)

    All plants will be Tall this is because the tall plant has the dominat gene. Meaning the offsprings will be Tall and have a recessive gene with the genotype of (Tt).

    Now what would happen if you cross a Heterozygous plant with a Short recessive plant.
    P1

    Genotype = Tt x tt

    Phenotype = Tall plant x short plant

    meiosis
    G1
    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

    Phenotype

    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 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

    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

    Image not found

    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

    Two Types of Mutations

    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

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    Frame-shift Mutations

    Chromosomal Aberrations/Chromosomal Mutations

    Types of Chromosomal Aberrations

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    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

    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

    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

    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

    Treatment

    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

    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

    Treatment


    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

    Arguments for genetic modification

    Arguments against genetic modification


    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:

    Now lets do an example

    Brown eye colour (B) is dominant over blue eye colour (b).

    Our pedigree

    Image not found

    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

    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

    Image not found

    Sensory nenron

    Motor nenron

    Connector nenron

    Parts of the neuron definination

    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 includes

    Peripheral nervous system

    Is made up of all the nerves outside the central 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

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    Cerebrum

    Medulla oblongata

    Hypothalamus

    Control centre for hunger, thirst, sleep, body temperature and emotions

    Cerebellum

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    The Spinal Cord

    Functions of the spinal cord


    Reflex action and Reflex arc

    Image not found Image not found

    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

    Image not found

    Disorders of the central nervous system

    Alzheimer's disease

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    Is a diseases that occurs when the nerve tissue within the brain appears to waste away.

    Symptoms

    Multiple sclerosis

    Image not found

    When the bodys own immune system attacks and destroys the myelin sheath causing a disorder called multiple sclerosis.

    Symptoms


    Effects of drugs

    Dagga (Marijuana or Cannabis)

    Heroin

    Ecstasy

    Tik

    Alcohol

    Cocaine


    The human eye

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    Structure of the ear and function

    Accommodation

    Image not found

    Is the adjustment of the shape lens to see clearly whether away or close by.

    Distant vision (objects further than 6m)

    Near vision (objects closer than 6)

    Pupillary mechanism

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    The pupillary mechanism (or pupil reflex) regulates the amount of light entering the eye by adjusting the size of the pupil

    Light is briht

    Light is dim

    Diseases and Disorders of the Eye

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    Long-sightedness (Hypermetropia)

    How to correct

    Short-sightedness (Myopia)

    How to correct


    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

    Is caused by bacteria

    Treatment

    Deafness

    Is caused by damages to certain parts of the ear

    Treatment

    Endocrine system

    What is an Endocrine System ?

    Our bodies consist of two kind of 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

    Hypothalamus

      ADH (antidiuretic hormone)

    • Target organ: Kidney
    • Controls the concentration of water in the blood

    Thyroid gland

    Thyroxin

    • Controls basic metabolic rate

    Adrenal gland

    Ovary (only females)

    Testes (only males)

    Pancreas: Islets of Langerhans

    Pituitary gland (hypophysis):


    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

    Treatment

    Homeostasis in humans

    What is Homeostatsis ?

    This enables the body to function efficiently ,despite changes in the external or internal environment

    Negative feedback mechanisms


    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


    Maintaining water levels (Osmoregulation)

    When the body has too much water

    When the body has too little water


    Maintaining salt/soduim levels

    When the body has too much salt

    When the body has too little salt


    The process of temperature regulation

    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

    On a cold day

    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


    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.

    Phototropism

    Is the growth movement of plant organs in response to the stimulus of light.

    Geotropism

    Is the growth movement of plant organs in response to the stimulus of gravity.

    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

    Advantages of Hormone weed-killers

    Disadvantages of Hormone weed-killers


    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

    Population

    Variation

    Sources of variation

    Things that bring about change amongst species(organisms).


    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

    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

    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...

    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:

    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:

    Why Lamarck's theory is rejected by most biologists


    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

    Darwin's Theory of Evolution by Natural Selection


    Difference between Lamarck's and Darwin's Theories

    Lamarck's Theory

    Darwin's Theory


    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

    Gradualism

    Theory of gradualism appiled for the stripes of tigers


    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

    Selection

    Significance

    Occurs in

    Importance

    Speed

    Effect on Evolution


    Speciation

    Speciation : means the formation of new species.

    Types of Speciation

    Allopatric speciation

    Sympatric speciation

    Speciation by Geographic isolation (Allopatric Speciation)

    Mechanisms of Reproductive Isolation

    Reproductive isolation or reproductive isolating barrier are factors that prevent two species from producing fertile offspring.

    Habitat Isolation

    Temporal Isolation

    Species-specific Courtship Behaviour

    Adaptation to Different Pollinating Agents

    Prevention of Fertilisation

    Hybrid Infertility


    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

    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

    Vertebrates

    Vertebrates can be sub-divided into the following classes

    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

    Three families exits with the Anthropoidea


    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

    The Brain

    Vision

    Number of offsprings produced

    Upright posture


    African Apes

    Humans


    Evidence of common ancestors for living hominids (including humans)

    Three main lines of evidence

    Fossil evidence

    Bipedalism

    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)

    Ardipithecus

    General characteristics of Ardipithecus

    Australopithecus

    General characteristics of Australopithecus

    Five well-known australopithecines

    Taung child (Australopithecus africanus)

    In 1924 the fossil skull of a hominin was found by Professor Raymond Dart at Taung, northwest of Kimberley.

    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.

    Lucy (Australopithecus afarensis)

    Lucy is a fossilised female skeleton found by Donald Johanson at Hadar in the Afar valley, Ethiopia in 1974.

    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.

    Australopithecus sediba (2 - 1,7 mya)

    HOMO

    General characteristics of Homo

    Homo species

    Homo habilis (handy man)

    Homo habilis lived in Africa, together with other Australopithecus species, about 2,2 - 1,6 million years ago.

    Homo erectus

    Homo neanderthalens

    Homo sapiens


    'OUT OF AFRICA' Hypothesis

    Evidence of african origins for all modern humans

    The following evidences support this hypothesis:

    Genetic links as evidence for the ‘Out of Africa’ hypothesis

    Different types of types of DNA are used:


    Arguments against Evolution

    People who do not believe in evolution put forward four main arguments aginst evolution. They say that:

    Some Alternate Theories of Diversity

    Human Impact

    The atmosphere and climate change

    Increased concentration of carbon dioxide in the atmosphere is due mainly to:

    Increased concentration of the methane in the atmosphere is due mainly to:

    Increased temperatures may lead to:

    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:

    Destruction of the ozone layer

    Ozone is a greenhouse gas that is found at low concentrations 15 – 50 km above the Earth’s surface.


    Availability of water

    The availability of water may be influenced by the following factors:

    Construction of Dams

    Destruction of wetlands

    Water wastage

    Cost of water

    Poor farming practices

    Droughts and floods

    Water recycling

    Quality of water

    The quality of water may be influenced by the following factors:


    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

    Droughts and floods

    Poor farming practices – monoculture, pest control, loss of topsoil and the need for fertilizers

    Alien plants and reduction of agricultural land

    The loss of wild varieties and the impact on gene pools

    Genetically engineered food

    Food wastage


    Loss of biodiversity

    Biodiversity refers to the variety of plant and animal species on Earth.

    Factors that reduce our biodiversity

    Farming methods

    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

    Deforestation

    Loss of wetlands and grasslands

    Poaching

    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.

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