Summer 2017 selection (b)

Explanation/disclaimer: click to expand/contract

Role of receptors and nervous system in increasing heart rate

This causes neurones to be sent along the sympathetic nervous system

These are detected by the motor neurones in the heart

The medulla oblongata will send the chemical signal along the sympathetic neurone

Baroreceptors and chemoreceptors detect changes in the aorta and carotid artery

Chemoreceptors in the wall of the casteroid arteries

Action potential is sent via the accelerous nerve

Baroreceptors detect the rise in blood pH due to increased CO2 levels

The electrical impulse is changed into a chemical, in order for it to diffuse across the synapses

The central nervous system which is either the spine or the brain

A relay neurone is not used as its a reflex action and it would take too long

Neuromuscular junctions are needed to create action potentials

The AVN sends an electrical wavelength across the atria

CO2 concn increases lowering the pH. It is detected by osmoreceptors

Neurons shoot to the brain and effectors travel to the heart

The nervous system is needed to send signals to the brain via relay, motor and sensory neurones

Receptors detect the presence of oxygen and glucose required for respiration, and if that isn't present, electrical impulses are sent down the nervous system

Cellular processes leading on from acetyl-CoA

This means that acetyl-CoA can bind to receptors on synapses

Fatty acid pathway and exercise

The fatty acids can be broken down into glucose

A human's biggest energy store per cm2 is lipids

How Sterile Insect Technique could reduce transmission of the virus causing dengue

When infertile males mate, they pass on radiation to their offspring

They don't reproduce so don't pass on infertility

The previous males could have immigrated to a different community

The number decreased steadily and then did not increase almost to 0

SIT would be complementary to receptors on post-synaptic neurone so it blocks receptor sites preventing virus from binding so electrical impulse is inhibited

As the sterile male does not contain the virus, it cannot transfer the virus to another mosquito

When they breed infertile offspring will be produced so die

If the virus is sterile it cannot inject its genetic material into a host cell

They are infertile so cannot breed and produce fertile offspring so cannot pass on the genes that cause dengue

Aedes aegypti cannot reproduce and pass on the virus to offspring

The alleles for dengue are not passed on to next generation if the fertile mosquitos breed with sterile, infertile males

Infertile males mean less successful fertilisation of women mosquitos

This will increase competition for females therefore resulting in more unsuccessful offspring produced

This decreases the birth rate of offspring with A. aegypti being born

Can't reproduce so can't produce offspring with dengue fever virus

Less mosquitoes would be carrying the virus (/). The gene would bcome a stronger allele. Genetic bottleneck could occur.

There is less chance of the disease being passed on to offspring

SIT will prevent the virus being inherited by the offspring of the Aedes aegypti

They may also be less aggressive if made infertile which would cause them to bite less therefore less chance of infecting humans

The infertile males will fight and if successful will mate with other mosquitos

Infected mosquitos will eventually die out

The gene of the sterile male mosquito will be changed by radiation. The offspring will have a possibility of not being the original

It will reduce the number of insects with the allele for being a carrier

Chance of mutations is lowered, gene pool is decreased and less genetically diverse

Exposure to the sterile virus would cause an immune response

Sterile males can no longer transmit dengue to females

Even if a diseased virus tries to mate and reproduce they are unable to pass on that virus to a new generation

Eventually they would die and the virus leaves with them instead of spreading

Other female mosquitos of the same species are more likly to breed with the sterile males which will not lead to offspring production

When sterile mosquito bites a person, virus is not passed on to person. Plus sterile male can mate with virus carrying female and not produce virus offspring

The sterile males would act like a competitive inhibitor

They are able to transmit the sterile form of the virus to people

Mosquitos with viral DNA in their cells are unable to breed with other mosquitos

When the SIT are released ...

Sterile mosquitos won't pass on the virus when mating

If they get the dengue, the mosquitos cannot pass the virus onto other organisms

Mark release recapture

Capture using an ethical random procedure

Collect sample of mosquitoes using a pitfall trap

Leave enough time for mosquitoes to reintegrate into society

Mark the mosquitos, release them into their habitat, then recapture the marked ones

Release the mosquitos back into their environment and ensure there is no immigration, emigration, births or deaths

Count the number that have been marked using a UV light source

The frequency of marked mosquitos in the mosquitos captured the second time can be used to estimate the original population size by dividing 100 by the frequency

After a week capture another sample and find how many have the virus

After a period of time which is not enough for them to mate but long enough to mix randomly with the rest of the population

Collect another sample a few weeks later (or the life cycle of mosquito later)

A sample will be taken using a quadrat

The second time only the mosquitos which had been marked are counted

Nerve cell communication

This causes temporary summation


ATP is required during the sliding filament theory of muscle contraction

Difference between mouse muscles

Trained mice had more ATP activity than controlled mice

Reasons for keeping water potential the same

If the water potentials were different water would move in and out by osmosis

Water potential might enter the chloroplasts in varying amounts

There is a chance that the chloroplast may shrink and burst due to osmotic pressure

Photosynthesis - light dependent reaction?
Why was tube containing DCPIP solution + no chloroplasts set up?

As a control test/tube to ensure that equipment is washed thoroughly

As a control to see the effect of nothing on DCPIP solution

To ensure that DCPIP would only react in the correct conditions

Chlorophyll absorbed light and electrons become exited

DCPIP is reduced by reducing sugars produced in photosynthesis

Advantage of IC50 (conc of chemical inhibiting decolorisation of DCIP by 50%)

It can be tracked as it is an isotope

It is measuring the change by a smaller amount so it is more accurate

The chemicals can be judged equally

It is an enzyme so it is only specific to DCPIP

It is effective at least half the time

It shows the concentration needed to decolorise half the solution

Comparison of Arbuscular Mycorrhiza Fungi on plant growth

Data may not be larger or representative

Use of a variety of DNA probes in detecting different viruses

The DNA probe is not likely to bind in a complementary way

The scientist produced a variety of primers in case one didn't work

Different primers are complementary to different ends of genes

There may be different base sequences that code for the same respiratory disease as it is a degenerate code

The virus may cause a mutation in base sequence so the primer may no longer be complementary

Different primers must be used for different people

A different primer is needed for each of the lengths of DNA wanting to be copied

Primers are specific to active sites of RNA

Primers may need to attach to different sections of RNA depending on if the virus is present or not

Biomass and primary productivity

The left over energy is used for mitosis which produces biomass

This cannot be converted into organic ions e.g. glucose

Gene pool definition

A location where there are different frequencies of alleles

Sympatric speciation

Alleles weren't shared between the two populations, causing a change in speciation between them

Their alleles changed to their genes giving them different characteristics

Sympatric speciation arises when two members are so far from each other they adapt and develop into two separate species over time

The two populations reproductive cycles are not in sink

Palm trees only mated with palm trees with similar characteristics

The trees couldn't flower and pollinate at the same time

Alzheimers disease in Andes

They are high in the mountain so genes are more likely to mutate

Why no natural selection against it?

Natural selection mainly affects recessive alleles

Natural selection requires an overproduction of offspring, but population is small

Health and other illnesses may increase the likelihood ..

Adults with the gene can still mate

In a small town it will take a long time for this to occur

There will be no alleles that dominate it for selection

Because they are isolated, people there have to mate with the people there

People don't live long enough for the mutation to have an effect

It is isolated so the gene pool will be low

The sample size is too small to be generalised

The mutation causes a degenerate code

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