While walking in the bush Paul hears a sound which he thinks is the roar of a lion.
He immediately runs to safety.
Describe how he hears the sound and describe the role of adrenalin to ensure that his
muscles are able to function efficiently while he runs away.
Hearing
- Pinna traps/directs the sound waves
- into the ear canal/meatus
- This causes the tympanic membrane to vibrate
- The vibration is transmitted to the auditory ossicles
- The ossicles amplify the vibration
- and transmit it to the oval window
- The oval window vibrates
- creating waves
- in the fluid/endolymph of the cochlea
- which stimulates the Organ of Corti
- to convert the wave into an impulse
- The impulse travels along the auditory nerve
- to the cerebrum where it is interpreted as the roar of the lion
Max 10
Role of Adrenalin
- More adrenalin is secreted
- Adrenalin increases muscle tone
- And causes the liver/muscles to convert glycogen into glucose
- The heart rate increases
- so that the muscles receive more glucose
- and oxygen
- needed for cellular respiration
- to provide the energy for the muscles to contract efficiently
- The rate of breathing increases
- and the depth of breathing increases
- to exhale carbon dioxide from the muscles faster
- and inhale oxygen faster
- Constriction of blood vessels to the gut/skin
- and dilation of blood vessels to the vital organs/brain/muscles
- allowing more blood to be supplied to vital organs/brain/muscles
Max 7
Fossils of the bipedal primates Ardipithecus, Australopithecus and early Homo species
are used to support the 'Out of Africa' hypothesis.
State the 'Out of Africa' hypothesis. Describe the evidence that supports the 'Out of
Africa' hypothesis and the evidence that shows that the three primate genera
mentioned above, were all bipedal.
HYPOTHESIS
- All modern humans*/Homo sapiens
- originated in Africa*
- and migrated to other parts of the world
FOSSIL EVIDENCE
- Fossils of Ardipithecus were found ONLY in Africa/Rift Valley/Ethiopia/South Africa
- Fossils of Australopithecus were found ONLY in Africa/Rift Valley/Ethiopia/South Africa
- The fossils of Homo habilis were ONLY found in Africa
- The OLDEST fossils of Homo erectus were found in Africa
- The OLDEST fossils of Homo sapiens were found in Africa
GENETIC EVIDENCE
- Mitochondrial DNA
- Is inherited only from the maternal line
- Analysis of mutations on this mitochondrial DNA
- shows that the oldest female ancestor were located in Africa
- and that all humans descended from her/mitochondrial Eve
- The Y chromosome shows the paternal line
CULTURAL EVIDENCE
- The OLDEST/most primitive artefacts (tools, cutlery, art etc.)
- were found in Africa
BIPEDALISM
The fossils of all three genera indicate that:
- The foramen magnum
- is located in a more forward position
- The pelvis
- is wider and shorter
- The spine
- is S-shaped
Describe how genetic variation is brought about in gametes through cell division and name and describe the specific process that takes place in the formation of an ovum.
Genetic variation is brought about in gametes through meiosis in two ways:
Crossing-over
- During Prophase I
- Homologous chromosomes/bivalents pair up
- Each chromosome has 2 chromatids
- Non-sister chromatids of the homologous pair overlap/cross over
- Points at which crossing-over takes place are referred to as chiasmata
- Genetic material is exchanged
- between non-sister chromatids
- After the process of crossing-over chromosomes have genes from its homologous partner
- This means that each gamete formed will have a mix of genes from maternal and paternal parents
Random arrangement of chromosomes at the equator
- During Metaphase I
- Each pair of homologous chromosomes
- *may line up either way/randomly on the equator of the spindle
- *Independently of what the other pairs are doing/ independent assortment
- During Metaphase II
- Each individual chromosome
- *may line up either way/flipped on the equator of the spindle
- *This means that gametes will have differing number/mix of maternal and
paternal chromosomes/chromatids
(at least 1 of the *compulsory and any 4 which could include compulsory points)
Formation of an ovum
- During oogenesis
- diploid cells
- in the ovary
- undergo meiosis
- to form a primary oocyte
- consisting of haploid cells
- One cell develops into an ovum
Describe the location, structure and functions of the DNA molecule and the process whereby copies of this molecule are made.
Location, structure and function
- The DNA is located in the nucleus/chromosome/genes/mitochondria
- DNA is a nucleic acid
- It has a doublestranded
- helix configuration
- consisting of building blocks called nucleotides
The three components of a nucleotide are as follows:
- Nitrogenous bases
- Phosphate portion
- Deoxyribose sugar portion(in DNA)
- 4 nitrogenous bases are A,T,C,G of DNA:
- adenine (A) bonds with thymine (T)
- cytosine (C) bonds with guanine (G)
- by hydrogen bonds
- Sections of DNA carry hereditary information
- DNA contains coded information for protein synthesis
Replication
- The double helix unwinds
- Double stranded DNA unzips
- as the weak hydrogen bonds break
- Each original DNA strand serves as a template
- Free nucleotidesbuild
- a new DNA strandonto each of the original DNA strands
- by attaching to their complementarynitrogenous bases/(A to T, and C to G)
- this results in two identicalDNA molecule
Plants and animals are both able to sense and respond to light.
Explain how plant stems respond to unilateral light and describe the path taken by light
through the human eye until it is converted into an impulse.
Plant stems response to unilateral light
- Plant stems response to light is positively phototropic
- Auxins
- produced in the tip of the stem
- move away from unilateral light
- so that there is a high concentration of auxins on the darker side
- which stimulates growth/cell division/cell elongation
- The low concentration of auxins on the side exposed to light
- inhibits growth
- This uneven growth
- causes the stem to bend towards the light
How humans receive and interpret light stimuli
- Light enters the eye
- through the cornea
- which refracts the light
- It then passes through the aqueous humour
- and the pupil
- The size of the pupil is adjusted by the iris
- to regulate the amount of light that enters the eye
- The light then passes through the lens
- which also refracts the light
- It then passes through the vitreous humour
- and reaches the retina
- which has the photoreceptors/rods and cones which convert the light stimulus into a nerve impulse
An ancestor of the elephant, Phiomia, had a long nose-like structure called a proboscis
which evolved into the trunk of the elephant. The proboscis was used to gather leaves
as food. The proboscis of Phiomia and the trunk of the elephant are shown below. The
diagrams have been drawn to scale.
Explain the evolution of the elephant's trunk in terms of Lamarckism and Darwinism as
well as the way in which an increase in the length of the trunk of the elephant could be
achieved through artificial selection.
Lamarckism
- The ancestral elephant stretched its proboscis
- to get leaves in trees/further from the body
- The more it used the proboscis,
- the longer it became
- The offspring then inherited the acquired longer proboscis
- Over many generations the length of the proboscis increased
- until it became a trunk as in the modern elephant
Darwinism
- There was a great deal of genetic variation amongst the offspring
- Some had long proboscis
- and some had short proboscis
- There was a change in environmental conditions/competition amongst the animals for food
- They had to reach higher in the trees to get leaves
- The animals with shorter proboscis died
- Those individuals with the longer proboscis survived
- They then reproduced
- and passed on this characteristic to their offspring
- The next generation of animals had a greater proportion of animals with longer proboscis
Artificial selection
- Humans select the elephants with
- desirable characteristics/long trunk
- and mate them to produce offspring with longer trunks
- Those that are pure breeding for long trunks
- are further selected to mate to produce offspring with further longer trunks
Explain the structural suitability of the sperm cell for its function and describe its involvement in the formation of a zygote and the development of this zygote until implantation.
Structural suitability of the sperm cell for internal fertilisation
- The front of the head of the sperm cell contains an acrosome/vesicle which carries enzymes to dissolve a path into the ovum
- Nucleus of the sperm carries genetic material of the male/ haploid number of chromosomes
- The middle piece contains mitochondria which release energy so that sperms could swim
- The presence of a long tail enables sperm cells to swim towards the ovum
- The contents of the sperm cell such as the cytoplasm is reduced/condensed making the sperm light for efficient movement
Fertilisation
- In the Fallopian tubes
- one sperm cell makes contact with the ovum's membrane
- The nucleus of the sperm enters the ovum
- Then the ovum membrane becomes impenetrableto other sperms
- The nucleus of the sperm fuses
- with the nucleus of the ovum
- to form a diploid zygote
- This is called fertilisation
Events after fertilisation until implantation
- The zygote divides by mitosismany times
- to form an embryo
- It first consists of a ball of cells
- called the morula
- which then develops into a hollow ball of cells
- called the blastula/blastocyst
- It embeds itself into the uterus lining/endometrium
- using chorionic villi
The unicellular zygote undergoes many developmental changes until it becomes a
multicellular foetus, nourished and protected by the mother.
Describe the changes that allow the zygote to eventually develop into a foetus and how
this foetus is nourished and protected during the period of pregnancy.
- The zygote divides by mitosis
- to form a ball of cells
- called the morula
- More mitotic divisions of the morula occurs to form a hollow ball of cells
- called a blastocyst
- The blastocyst attaches to the endometrial lining
- The outer wall of the blastocyst, called the chorion,
- develops projections called villi which
- embeds/implants into the uterine wall
- The cells of the embryo continues to divide
- and differentiate
- to form the different organs and limbs
- and is now called a foetus
- The foetus is enclosed in a sac called the amnion
- filled with amniotic fluid
- which protects the foetus against temperature fluctuations
- protects the foetus against dehydration
- and protects the foetus against mechanical injury/acts as a shock absorber
- The chorionic villi and the endometrium form the placenta
- where the blood of both the foetus and the mother
- run close to each other
- allowing for nutrients to diffuse into the blood of the foetus
- The umbilical vein
- carries the absorbed nutrients from the mother to the foetus
Describe how Lamarck and Darwin explained evolution, and compare Darwin's ideas to the ideas of Punctuated Equilibrium.
Lamarck explained evolution using the following two 'laws':
The law of use and disuse:
- As an organism uses a structure or organ more regularly, it becomes better developed or enlarged in that organism.
- If an organism does not use a structure or organ frequently, it becomes less developed or reduced in size and may disappear altogether in that organism
The inheritance of acquired characteristics:
- Characteristics developed during the life of an individual
- (Acquired characteristics) can be passed on to their offspring.
Evolution according to Darwin
- Organisms produce a large number of offspring
- There is a great deal of variation amongst the offspring
- Some have favourable characteristics
- and some do not
- When there is a change in the environmental conditions/or
- there is competition
- Then organisms with characteristics which are more favourable survive
- Whilst organisms with less favourable characteristics die
- This is called natural selection
- The organisms that survive reproduce
- And thus pass on the favourable characteristics to their offspring
- The next generation will therefore have a higher proportion of individuals with the favourable characteristics
Darwin's ideas about gradualism compared to Punctuated Equilibrium
- Darwin believed that evolution takes place through an
- accumulation of small
- gradual changes that occur over a long period of time
- supported by transitional forms in fossil record
- Punctuated equilibrium suggested that evolution sometimes involves long periods of time where species do not change/very little change occurs
- This alternates with short periods of time where rapid changes occur
- New species are formed in a short period of time/relative to the long period of no/little change
- supported by the absence of transitional forms
Describe the process of protein synthesis and the way in which this process would be affected by a gene mutation.
PROTEIN SYNTHESIS
Transcription (T)
- Double stranded DNA unwinds
- and unzips when
- the hydrogen bonds break
- and this is controlled by enzymes
- One strand is used as a template
- to form mRNA
- using free RNA nucleotides from the nucleoplasm
- The mRNA is complementary to the DNA
- mRNA now has the coded message for protein synthesis
Translation (S)
- mRNA moves from the nucleus/to the ribosome
- Each tRNA carries an amino acid
- tRNA carries the amino acid to the ribosome
- When the anticodon on the tRNA
- matches the codon on the mRNA
- Amino acids become attached in the sequence determined by the mRNA
- by peptide bonds
- to form the required protein
EFFECTS OF A MUTATION (M)
- A gene mutation affects arrangement/type of the nitrogen bases/nucleotides
- This changes the code on the DNA
- which changes the code on the RNA
- A different amino acid may be coded for
- which causes a change in the amino acid sequence in the protein
- leading to the formation of a different/alternate/no protein
A goalkeeper in a soccer match prevented a goal from being scored when he dived to his right after the ball was kicked towards him. Just before he dived, he heard his team
Describe how his eyes adjusted to see the ball as it travelled towards him and describe how he heard his team-mate and maintained his balance as he dived to save the ball.
As the ball moved towards the goalkeeper:
- Accommodation took place
- Ciliary muscles contracted
- Suspensory ligaments became slack
- This reduced the tension on lens
- Lens became more convex/round
- Refractive power of the lens increased
- Image of the ball fell on the retina
Hearing
The shout of his team-mate was heard by the goal keeper as follows:
- The sound waves were directed by the pinna
- through the auditory canal
- to the tympanic membrane/eardrum
- causing it to vibrate
- The vibrations of the tympanic membrane were transferred to the ossicles in the middle ear
- which eventually caused the oval window to vibrate
- This set up pressure waves in the cochlea
- This stimulated the Organ of Corti in the cochlea
- to convert this stimulus into a nerve impulse
- which was then transmitted along the auditory nerve
- and interpreted in the cerebrum
Balance and equilibrium As he dived:
- A change in the direction and speedof the body
- causes the movement of fluid in the semicircular canals
- which stimulates the cristae
- A change in the position of the head
- stimulated the maculaein the utriculus and sacculus
- The stimuli were converted into impulses
- which were transported along the auditory nerve
- and interpreted in the cerebellum
- which then sent impulses to the muscles
- to restore balance and equilibrium
Describe how meiosis and different types of mutations contribute to genetic variation and the role of this variation in natural selection.
Meiosis
- Crossing over
- occurs during prophase I
- Homologous chromosomes / chromatids overlap
- at points called chiasma/ chiasmata
- Genetic material is exchanged
- resulting in new combinations of genetic material Max 3
- Random arrangementof chromosomes
- occurs during metaphase
- so that they separate in a random/ independent manner
- resulting in new combinations of genetic material
Mutations
- A gene/ (point and frameshift) mutation occurs
- as a result of a change in sequence of nitrogen bases in the DNA molecule
- A chromosomemutation occurs as a
- result of a change in the structure of a chromosome/ number of chromosomes during meiosis
- Mutations that occur in sex cells
- are passed on to the new generations
- creating new characteristics
Role of variation in natural selection
- Organisms of a particular species shows a great deal of variation
- Some individuals may have characteristics that are favourable / any example
- Others may have characteristics/any example that are unfavourable
- If there is competition/changing environmental conditions/ Selective pressure by the environment
- organisms with favourable characteristics survive
- and reproduce
- and pass this favourable characteristics to their offspring
- while organisms with unfavourable characteristics will die out
- Over time the whole population will have this favourable trait
Name the hormones produced by the testes and ovaries and describe the role of each hormone in human reproduction.
Testosterone
Produced by seminiferous tubules in the testes During puberty testosterone stimulates:
- The deepening of the voice as vocal cords elongate in the larynx
- The development of muscles
- The growth of facial, pubic and body hair
- Development of the penis and testes
- The production of sperm in the testes
Oestrogen
Produced by the Graafian follicles in the ovaries
- Causes the lining of the uterus/endometrium
- to become thicker/more vascular
- in preparation for a possible implantation of the embryo and development of the foetus
During puberty oestrogen stimulates:
- The widening of the pelvis/hips
- The growth and development of the breasts
- The growth of the female sex organs
- The start of the menstrual cycle, ovulation and menstruation
Progesterone
Produced by the corpus luteum and placenta
- Progesterone causes further thickening of the endometrium
- so that it is ready for implantation of the embryo should fertilisation occur
- High levels of progesterone
- inhibits the secretion of FSH
- by the pituitary gland
- which in turn prevents the further development of any new ovum in the ovary
The development of a new species
- If a population splits into two populations.
- There is now no gene flow between the two populations.
- Since each population may be exposed to different environmental conditions,
- Natural selection occurs independently in each of the two populations
- such that the individuals of the two populations become very different from each other
- genotypically and phenotypically.
- Even if the two populations were to mix again,
- they will not be able to reproduce with each other, thus becoming different species
The development of bipedalism
- The backward position of the foramen magnum on the skull,
- the narrow pelvis
- and the less-curved spine
- indicates that the ape-like beings were quadripedal (any 3)
- The forward position of the foramen magnum on the skull,
- the wider pelvis
- and the curved spine
- indicates that modern humans are bipedal
Change in the diet from raw food to cooked food
- The large teeth, especially the canines
- as well as the large and long jaws
- which makes the skull prognathous
- as well as cranial/brow ridges associated with large muscles that operate the jaws
- indicate that the ape-like beings ate raw food that required a great amount of processing/tearing, biting and chewing. (any 3)
- The smaller teeth, including the canines
- as well as the smaller jaw size
- which makes the skull less prognathous
- as well as the absence of cranial/brow ridges due to the presence of smaller muscles for chewing
- indicate that modern humans rely on a diet of cooked food that does not require the same amount of processing/tearing, biting and chewing.
Start with a cell containing FOUR chromosomes and describe ALL the chromosomal changes that occur during meiosis, resulting in the formation of abnormal gametes due to non-disjunction in meiosis 1.
- Each chromosome shortens and becomes visible
- as two chromatids
- joined by a centromere
- Homologous chromosomes come to lie next to each other
- Chromatids from each homologous chromosome overlap/crossing over occurs
- The point of overlap is called the chiasma
- Genetic material is exchanged between the homologous chromosomes
- The chromosomes line up along the equator
- in homologous pairs
- attached to the spindle fibres
- When the spindle fibres shorten/contract
- * All 4 chromosomes are pulled to one pole due to non-disjunction
- Resulting in two cells
- * one with 4 chromosomes,
- * and one with no chromosomes.
- The cell with 4 chromosomes undergoes meiosis 2
- The 4 chromosomes line up at the equator
- in a single row
- When the spindle fibres shorten/contract
- the centromeres split
- and chromatids/daughter chromosomes
- are pulled to the opposite poles of the cell
- Two cells result
- * Each with a nucleus containing 4 chromosomes
- * Resulting in diploid gametes
Nontobeko had been walking in the desert, without water, for two days, when she
suddenly heard a sound behind her. She turned her head and saw a snake coming
towards her. She became scared and turned around to run away. As she was running,
she tripped and fell.
Describe how her body regulated water content during the two days and describe how
her balance would have been restored after she fell down.
Regulating water
- The water levels in her body are low/she is dehydrated
- Osmoreceptors
- in the hypothalamus are stimulated by the low water levels and send impulses
- to the pituitary gland/hypophysis
- which is stimulated to secrete more ADH
- ADH increases the permeability
- of the tubules/collecting ducts and distal convoluted tubules
- in the kidneys
- More water is reabsorbed
- and passed to the surrounding blood vessels
- Less urine is produced
- and the urine is more concentrated
- in order to conserve water
- Aldosterone is secreted by the adrenal glands
- to ensure more Na+ ions are reabsorbed by the distal convoluted tubules
- The increase in Na+ ions in the blood
- causes more water to be reabsorbed into the blood capillaries
Balance is achieved in the following way:
- The maculae
- in the utriculus and sacculus and
- the cristae
- in the semi
- circular canals are stimulated
- They generate impulses
- which is transmitted through the auditory nerve
- to the cerebellumwhere they are interpreted
- Impulses are transmitted via the motor neuron
- to skeletal muscles
The anole lizard of the Caribbean Islands represents a group of about 150 closely
related species, which evolved within the past 50 million years from a single species.
Use this example to describe how natural selection led to the process of speciation that
gave rise to the 150 different species of lizards.
Natural selection and speciation
- The original species of anole lizards was separatedS
- into different populationsS
- by a geographical barrierS
- which is the seaS
- There was no gene flowS
- between the separated populationsS
- Each population was exposed to different environmental conditionsN on each island
- Because there is variationN amongst the lizards
- Natural selection occurred independentlyN in each population
- Some had favourable characteristicsN to survive on a specific island
- while others did notN
- The ones that did not have the favourable characteristics died N
- The ones with the favourable characteristic survived N
- and reproduced N
- to pass the gene for the favourable characteristicsN
- to the next generation N
- And over many generations the favourable characteristic becomes more frequent in the population N
- each population became different from the otherS over time
- genotypically S
- and phenotypicallyS
- Even if the populations were to mix againS
- they would not be able to reproduce/interbreed with each other