Explain the three types of selection forces we discussed? (5 marks)
- Directional Selection: occurs when a certain extreme trait becomes much more adaptive and beneficial to species
- Stabilizing Selection: would occur when neither extreme of the trait is beneficial but the normal or middle
variation of the trait is
- Disruptive Selection: occurs when both extremes of the trait are adaptive and beneficial to species survival.
1. Please explain whether scientists think evolution has a purpose? --OR --On the basis of Darwinian Theory, do you
think that appearance of species was just a lucky coincidence or was it inevitable that Homo sapiens have
evolved? (3 marks)
- Is purposeless change resulting from random variation
- Mutation ( genetic variation) is the basis of variability upon which natural slection works.
- Evolution is change in allele frequencies from generation to generation.
- It doesn’t work toward a specific direction species must move, it’s completely random.
- However, species if able to adapt to the environment and reach their reproductive age, will survive.
- There have been trillions of accidental events that led to the existence of all current life on the planet.
- Homo sapiens have evolved to cope with certain environments and perform particular tasks.
2. Briefly describe the function and structure of DNA. (5 marks)
DNA is a base pair helical molecule with two twisting sugar-phosphate back bones attached to each other by pair
Have 4 building blocks (nucleotide bases): Adenine, Thymine, Guanine, and Cytosine.
5”prime (beginning) and 3”prime (end) is the position of basis relative to sugar molecules in DNA backbone.
it’s structure is a mechanism for heredity
Info in DNA guides the cells to make new proteins( aminoacids)
that determine all of our biological traits that get passed to next generations. 2
3. What is an action potential and how is it generated? Please describe the process? (6 marks)
The action potential is the change in the cells voltage. Is a quick reversal of the negative resting potential from -
65mv to +40mv
it can be inhibitory or excitatory. An action potential can be generated in numerous ways.
The integration of EPSP and IPSP would generate a potential. All or none phenomenon (it either occurs or it
When electrical signals inside neurons travel through to the target neuron. These signals can be carried out by
TEMPORAL or SPATIAL summation.
an excitatory postsynaptic potential (EPSP) is a temporary depolarization of postsynaptic membrane potential caused by
the flow of positively charged ions into the postsynaptic cell. They are the opposite of inhibitory postsynaptic potentials
(IPSPs), which usually result from the flow of negative ions into the cell or positive ions out of the cell
1. The electrical signals(EPSP) brings the neuron to threshold; Na+ channels will open and a lot of Na+ will rush into
the cell making the cell positive inside (depolarization). (rising phase)
2. At the peak of the potential Na+ channels will start closing and K+ channels will open. (overshoot phase)
3. K+ will exit the cell; hyperpolarizing it. (repolarising phase)
4. K+ will exit too much (undershoot phase)
5. All K+ will close ( recovery phase)
6. Cell will return to resting potential. (-65mv)
4. Please revise what happens when an action potential reaches presynaptic terminal and how the signal is
transmitted to postsynaptic terminal. (8 marks)
Communications among neuron occurs at specialized junctions called “synapses”.
most common type of synapse is the chemical synapse
Synaptic transmission begins in a chemical synapse in a Nervous system, when a nerve impulse reaches the
presynaptic axon terminal.
depolarization of presynaptic membrane initiates sequence of events leading to transmitter release and activation
of receptors on post synaptic membrane.
Some principle molecules and organelles necessary for the release of neurotransmitters :
o Ca2+ channels, and Ca2+ ions.
o synaptic vesicles
o transmitter molecules
o synaptic cleft
o post synaptic receptors 3
i) when presynaptic neuron is depolarized—voltage gated calcium channels open and calcium ions rush into the
ii) some of these calcium ions bind to protein on synaptic vesicles membrane( synaptotagmin)
iii) These synaptic vesicles then move to the presynaptic membrane and both (synaptic vesicle membrane and
presynaptic membrane are drawn together by SNAREs)
iv) once these two are fused, they release neurotransmitter molecules into the synaptic cleft
v) These transmitter molecules bind to receptor molecules in post synaptic membrane. Excitation or inhibition
depends on the particular neurotransmitters and their receptor combination.
vi) receptors open, Na+ comes into the cell generating Excitatory post synaptic response
vii) AChE in the synaptic cleft, breaks down ACh >>A +Ch
viii)release of receptors causes channels to close
ix) left over neurotransmitters from the cleft are taken back to presynaptic terminal by TRANSPORTERS
x) They are refilled by synaptic vesicles so they can be recycled.
xi) a spike in presynaptic cell, will stimulate a spike in post synaptic cell.
5. What is LTP? How is it induced and measured? What is its relevance to behaviour? (6 marks)
Long term potentiation is the persistent increase in synaptic strength following high frequency stimulation of a
Synapses that have undergone LTP tend to have stronger electrical responses to stimulation than other synapses.
Increase in synaptic strength or potentiation lasts a very long time compared to other processes that affect
An increase likelihood of cells firing A.P/ in response to a constant synaptic input LTP long lasting and involved in
many memory formations
Contributes to learning and memory.
6. Explain why behavioural characteristics don’t often follow Mendelian Inheritance? (4 marks)
There is a tendency to think that there are genes for particular behaviour.
Some part of genetic material of individuals causes variation in physical structure of that behaviour
That structure in turn causes specific behaviour changes under particular combination of env. Circumstances.
Thus, behaviour is influenced by BOTH env. And genetics.
For law of dominance: not all alleles are dominant or recessive one has alleles that express co-dominance and
incomplete dominance where both traits are visible to some extent.
Law of independent assortment: some genes are linked which would imply that when asserting they would assert
together. i.e. A+B-> C 4
7. Please explain the foraging behaviour strategies of the sitter and rover larvae of the fruit fly and explain why
scientists think these two strategies coexist in nature? (3 points)
Rover Larvae moves significant distances and feed as they go. (70%)
sitter larvae moves much less and tends to feed on one cluster of food (30%
these two strategies exist due to varying densities of the population
Rover is good when population is dense, because there is more competition and food recourses are patchy and
dispense and one has to get them.
When population density is low, sitter is best. Because food is present in larger patches and not lots of
competition is required. Therefore, less movement is required, and less energy is wasted.
8. What is an optimal foraging strategy is with regard to choosing certain prey items. If you can, please use a
mathematical equation and explain what it predicts? (5 marks)
Mathematical equation: E2/T2 > E1/ (S1+T1) (E) Amount of energy (T) Time.
Optimal foraging theory make the assumption that animals make choices that will maxime their net energy gain ,
the animal will take into account not only the amount of caloric value of food , but also the energy cost involved in
processing and eating it.
Energy divided by time E/T , allows the prediction of profitability
In this case the equation describes
Big prey (profitability= E1/T1)
Small Prey( profitability= E2/T2
S1 = the time taken to search for new prey).
where big prey are energetically the most profitable (E1/T1 >E2/T2)
when the animal encounter a small prey
It should eat if the amount of extra “profit” a big prey would yield is greater than the amount of energy it will spend
in the search (E2/T2 > E1/(S1 + T1), where S1is the time taken to search for new prey).
9. Why do you think that foraging in groups may be advantageous and are there any costs associated with foraging
in groups? (4 marks)
o adding protection- decrease predatory risk
o adding food intake- decrease vigilance ( more perception all together)
o ability to hunt larger prey
o sharing prey
o fast depletion
flock size is affected by : feeding, interference, vigilance
10. Please explain what conditioned taste aversion is and also explain why this form of conditioning is considered
quite different from other classical conditioning phenomenon. (3 marks)
CTA-> eating a substance, followed by an illness, and then avoiding that substance
It’s different from other Classical conditioning because unusually long delays between CS (taste) and UCS (nausea)
and unusually long lasting memory. Conditioned Response= food avoidance 5
11. Please explain the molecular mechanisms underlying e