Summer 2015 selection (a)

Explanation/disclaimer: click to expand/contract

Reasons why male and female life expectancies differ

Breast cancer is more popular than prostate cancer

Men have testicals (sic), women don't, and can obtain testicular cancer

Females are more health conscious ... as they put weight on more easily

Ammonification ...

... is the process where microorganisms convert the ammonium in plants into the soil

Bacteria feed on ammonium compounds, often dead

During nitrogen fixation, nitrifying bacteria convert nitrogen gas into ammonium ions

Ploughing ...

... would rotate the soil

spreads nitrate under the plants roots

stops nitrogen leaving to become nitrogen gas in the atmosphere

prevents water filling in the soil

would remove nutrients from the soil which would be needed for new crops

will dislodge the soil and weaken its strength

distributes the nitrates through the soil better therefore more denitrification occurs

breaks up the soil releasing glucose

When soil is aerated nutrients are added

Crop rotation ...

... allows plants to die and be decomposed

makes soil less hostile

If a pest is interested in a certain crop it will not return if it is not available

Different crops add different nitrates to the soil

It will take time for predators of the crop to find the field

Growing leguminous plants in alternative years mean more nitrogen is found in the soil

Nitrates formed from previous crops will remain in the soil to be used for the next crop

Explanation of decrease in gross productivity as woodland matures

Rate of growth begins to slow and so the plants and trees will expell less energy

More larger plants are producing energy

First 20 years of succession

Pioneer species have survival allele so environment is less hostile fot them

After 100 years of succession

The community had become climaxed

Reasons for conserving woodlands

We can use woodlands to make vaccines

This maintains high gene pool for economic growth

To save habitats for human pleasure

so woodland does not get out of control

other species have the right to live on this plant as well

Explanation of no male tortoiseshell cats

Men only have one allele

The allele for fur is not usually present on Y

The Y chromosome is recessive

Males have an XY chromosome

So only one colour cat can be

Description of variations in genotype frequency due to selection

Over time the frequency of alleles will fall

[Suggest and (?)] Explain why rate of photosynthesis is low between light wavelength 525 & 575 nm

The temperature between 525nm and 575nm might not have been the optimum

This did not stimulate the electrons to leave the chloroplast

This could be due to the light bulb losing its power

Light needs to be able to enter the thylakoid membrane for pS to occur

Perhaps the light was coming in at an angle

This may not be the optimum temperature for enzymes

Light passed through and missed the chlorophyll molecules

It is not the wavelength for that colour of algal cells

This wavelength may not be accepted by chlorophyll

It must use the light independent reaction

The wavelength was the perfect size to reflect off the algae

This is due to a change in the pH conditions from the previous photosynthesis rate

At these wavelengths other cells which need light absorbed it more easily

Light does not enter the chlorophyll as easily and make contact with photosystem II

This wavelength of light is not within the green spectrum

This is not the best wavelength for photosynthesis

The leaves couldn't convert this wavelength of light into energy

The chlorophyll in the leaf may be less adapted to use this wavelength of light

These wavelengthe may be the wrong size to be absorbed by the chlorophyll

The chlorophyll was unable to utilise the entirety of this wavelength

They get enough light in other wavelengths so there is no need to use that wavelength

These wavelengths may have been absorbed as heat

Another abiotic factor may have been a limiting factor e.g. carbon dioxide

This wavelength is obviously less intense than before 525 and after 575 PS would be less due to light intensity being a limiting factor

Perhaps this reached the light compensation point

Not optimal level of light intensity for pH build-up of photosynthesis

The wavelength could be mainly red or blue therfore they are reflected off the plant

Wavelength was not of the correct size and therefore frequency

Algal cells don't normally experience these waves of light

Comments on enzyme binding stages

The substrate shape will change

OAA is a non-competitive inhibitor, meaning it binds to anywhere on the enzyme except for the active site

This warps the active site so it becomes complimentary to acetylcoenzyme A

It binds to the active sight

Consequence of converting pyruvate to lactate

This process frees up phosphorous molecules

Consequence of converting lactate back to pyruvate

Pyruvate can enter the Krebs cycle, causing 38 ATP to be made

Climate change and soil salinity

Global warming will affect soil sanity

Climate change means some of the oceans will disso;ve

Crop growth problems in saline soil

It will lower the water potential of the soil so that it can no longer travel by osmosis

Water will want to stay in the saltier ground

This will lead to a decreased concentration of other things like water

Salt is insoluble and can therefore inhibit macronutrients from moving into the plant's root system

Osmosis can't occur

If the soil becomes too salty the pH will increase

This will result in plant cells becoming turgid

No osmosis takes place so nutrients aren't taken up

This causes osmotic lysis (cells fill with water and then burst)

The high volumes of soil salinity mean that the soil can't get rid of it so it remains in the plant

Higher salinity means less nutrients such as nitrates in the soil

Misinterpretation of the term isolated

The fungus was kept separate so it did not infect other plants

This decreases the risk of selecting from one anomalous cucumber

Evaluation of test results

The results showed a large standard error meaning they could do better

All the standard errors overlap so none of the results are significant

Standard errors overlap so significance is not different

All other treatments have less mean diseased plants

Why were weeds removed (in cucumber growth experiment)?

The weeds would take glucose out of the soil

Explanation of how different species of lizard evolved on Caribbean islands:

Certain phenotypes were favoured e.g. less fur in hotter regions

The islands budded off from the mainland

The Caribbean has evolved through speciation

Variety in the population can lead to mutations arising

Environmental changes led to a mutation in alleles

There may have been mutations to help the species to survive

It cannot produce offspring with the species it used to be apart of

Variation arises in the mutation in the genes or DNA

These organisms migrate to conditions they are better adapted for

Mutations between the different populations could have occurred

The characteristics which will be favourable on that island will be prominent

This would eventually lead to both species becoming so similar that they ended up being part of the same genus

The species from mainland USA may have come back to live with the newly evolved species, but ...

The lizard with the new allele reproduced and reduced the size of the gene pool

Mutation caused some advantageous characteristics to occur (caused by alleles)

Lizards that are mutated are better suited to the environment

Now the most favourable combination of alleles survive and reproduce

Species with alleles towards the extreme ends would survive

Variation occurs through mutation due to selection pressures

This narrows the gene pool

Description of the mark-release-recapture method to estimate the number of a species of lizard on a small island

Select a number of required lizards you wish to mark

The marking system should not make them any more of a threat to predators

After a period of time, random lizards would be caught

The amount marked symbolises the amount of lizards

Release any captured lizards of different species

Mark it inconspicuously so as not to make it vulnerable to pray

You would set up a study area where there is a definite boundary so that no organisms can enter or leave

Explanation of the variation in CO2 concentration in a tropical forest

CO2 is taken in through the stroma of the leaves

At low heights CO2 is higher

At greater heights it is colder so more respiration must occur to increase the heat

In the night there is no photosynthesis so plants must respire

It may be higher in the day as they respire at a faster rate to cool down and catch food

At night only the light independent reactions (respiration) occur

In the morning CO2 levels will be high due to a night of respiration

The concentration of CO2 will be lager during the day

At ground level CO2 is higher

Photosynthesis is lower at ground level

At low height there is more CO2 as heat is trapped

The tall trees are closer to the atmosphere

At higher points above ground the oxygen dissociation curve of organisms will move according to their surroundings

Over 24 hours it will be both light and dark for some time

As the day progresses the sunlight will travel higher up from ground level

At night time respiration occurs and light independent photosynthesis

Ps happens during the day, respn happens during the night

CO2 is taken up by chlorophyll in chloroplasts for photosynthesis

Below ground, less light is available therefore less photosynthesis    Home     Contents     Contact via form     Contact via email     Howlers     Books     WWWlinks     Terms of use     Privacy