Turn on thread page Beta

UNOFFICIAL MARK SCHEME: AQA A Level Biology 20/06/2017 Paper 2 watch

Announcements
    • Thread Starter
    Offline

    20
    ReputationRep:






    :banana: A special thanks to DrNippleson for helping out with their contributions! :awesome: :banana:






    This thread is for paper 2! There have been a lot of people asking for this thread, and of course I'm delivering! Like before, I don't really remember many of the questions so I'm calling all Biology students to contribute whatever they can to help us all out!

    Also, potential essay topics for paper 3 (based on what has already come up) - again, please feel free to come up with your own:
    -Biology importance of cycles (Krebs, Calvin, Nitrogen etc.)
    -Biological importance of ions (Kidneys and nerve impulses didn't come up much)
    -Importance of transport (Haemoglobin, Plant transport, Mass transport like heart)
    -Importance of proteins (structural proteins, ADN replication, protein synthesis, antibodies, transport across membranes, photosynthesis, digestion
    -Pressure and pressure gradients, eg tissue fluid, the phloem, heart, lungs, nephron

    Like before, press the "show" button below to see what we've already got!

    Spoiler:
    Show





    Exercise increases the heart rate, explain how receptors and the nervous system are involved. (4 marks)
    Chemoreceptors in the carotid arteries detect the increased CO2/decrease in O2 in the blood, sending a signal to the medulla oblongata which sends an impulse down the sympathetic neurone in the autonomic nervous system. When it reaches the sinoatrial node, it secretes noradrenaline which causes impulses to occur more rapidly, increasing the heart rate.

    Suggest an advantage of AMPK during exercise (diagram) (3 marks)

    Why would releasing sterile males would reduce the chance of the spread of infection in humans? (2 marks)
    Sterile males compete with fertile males for resources and females/use resources but have no offspring. Carrying capacity of ecosystem for population does not increase so overall smaller breeding population, so fewer chances for disease transmission.

    Explain how the scientists would use the mark-release-capture method to determine the population size (3 marks)
    -sample 1
    -mark
    -release
    -wait
    -sample 2
    -pop = # in A * # in B / # of A in B
    -assumes even distribution of mark during wait time, that number of A in B is representative of number of A in population, population is isolated, birth and death rates are low, mark stays on, mark doesn't affect behaviour.

    Explain why the treatment wasn't effective (1 mark)
    Sterile males do not out compete fertile males/generations produced quickly so sterile population becomes insignificant/radiation sterilisation not permanent?

    Explain why the transgenic mosquitoes were released in week batches? (2 marks)
    Add more to population as offspring die before reproducing, so to prevent population size increasing as allele becomes extinct b/c not passed on, external supply of allele is provided in the form of transgenic mosquitos.

    Using all the information provided, evaluate the use of transgenic mosquitoes (4 marks)

    Explain the difference between the staining (2 marks)
    In untrained mice, they have less myoglobin which is found in slow-twitch muscle and contains stores of oxygen for aerobic respiration.

    Group B could last longer than Group A, explain why (3 marks)
    The trained mice have more slow-twitch muscle so they are able to aerobically respire, providing more ATP than untrained as they mainly anaerobically respire, so they have more ATP for muscle contractions and can thus exercise longer. Also it limits the amount of lactic acid that is built up.

    They have more of the dehydrogenase enzyme which is used in the krebs cycle - so they produce more ATP aerobically than anaerobically, and hence they produce less lactate which leads to less muscle fatigue

    What was the average diameter of each cell? (2 marks)
    84um
    (Area)/Pi = R^2
    sqrt(r^2) = r
    r*2 = d
    d/15 = mean

    mean (mm to um) * 1000 = 84.10

    State two differences between young and adult males (2 marks)

    How does the fungi get nutrients (2 marks)

    Evaluate the use of AMF across all phosphate concentrations (4 marks)

    Suggest why the water potential was the same (2 marks)
    So there was no water potential gradient that would draw water into the chloroplasts by osmosis and potentially cause them to burst.

    Explain why Tube 1 was set up (2 marks)
    To show that there was no colour change without the chloroplasts/to show that it is the chloroplasts that were having an effect

    Explain the results in Tube 3 (2 marks)
    As the chloroplasts photosynthesise, they produce reduced NADP. The DCPIP accepts these electrons to regenerate the NADP, thus becoming reduced and changing colour.

    Why is using an inhibitor of the reduction of DCPIP a way of reducing weed growth? (2 marks)

    What does reverse transcriptase do? (1 mark)
    Uses a strand of mRNA to produce a complementary strand of DNA (cDNA)

    What does DNA polymerase do? (1 mark)
    Catalyses the condensation raction to form phosphodiester bonds between the nucleotides.

    Explain why the DNA was hydrolysed (2 marks)

    Calculate the ratio of A to B (2 marks)

    Why did the PCR reaction stop? (1 mark)
    All of the free-floating nucleotides had been used up to produce new DNA strands

    Explain why primers were added to the DNA sample (2 marks)

    What is meant by phenotype? (2 mark)
    The observable characteristics of an organism, determined by genetic and environmental factors.

    What type of gene interaction is the diagram displaying? (1 mark)
    Epistasis

    What are the colours of the genotypes? (2 marks)

    Work out the offspring's genotypes, phenotypes, and phenotype ratio (~3 marks)
    Genotypes:
    Phenotypes: White : Green : Yellow
    Ratios: 2 : 1 : 1

    Work out the percentage that were heterozygous (Bb) using Hardy-Weinberg. (2 marks)
    32%


    Why shouldn't the pancreas transplant be used for people with type II diabetes? (2 marks)
    Type II can be treated with regular exercise and diet so no need to risk surgery. Other point was that in type II the beta cells still produce insulin but insulin receptors are damaged so would be ineffective

    Tick the box that incorrectly describes the role of insulin (1 mark)
    D. Activates glycogenolysis reactions

    Describe how transcription factors turn adult skin cells into iPS (2 marks)
    Negative transcription factors (repressors) are used to stop the expression of specialised genes, whereas positive transcription factors (activators) are used to activate the expression of genes associated with pluripotency.

    Evaluate the use of the iPS cells in humans. (~3 marks)
    The transplant was successful in mice as after the first week there was similar blood glucose levels to non diabetics however for mice it showed more fluctuations than the non diabetic group.

    However since it was done in mice, although mice are mammals like humans, there are possible unknown side effects in humans or the treatment may not be effective in human as the transplant cells may be rejected by the immune system and the long term effects are not known in humans so further tests needed.

    It needed more trials and a larger sample size to see the true trend as the glucose levels were going up gradually (while fluctuating still) after the transplant in diabetic mice.

    What is a gene pool? (1 mark)
    All of the genes in a population


    Explain how two species of palm tree came about due to sympatric selection, where their flowering times are different (5 marks)
    * No gene flow between populations
    * Mutation occurs
    * Increases chance of survival to reproduce
    * Offspring with beneficial allele produced, differential reproductive success continues
    * Allele frequency increases
    * This mutation occurred in both populations
    * Populations diverge to the point of being different species as allele frequnecy changes; they can no loner reproduce to give fertile offspring

    People develop AD every 30 seconds. By what percentage did the amount of people increase (presuming nobody died) (2 marks)
    ((1*2*60*24*365.5)/5400000) * 100 = 19.5%

    Why does the inhibition of acetylcholinerase improve nerve communication in AD sufferers? (3 marks)
    Acetylcholine is not broken down, allowing it to repeatedly stimulate action potentials, which makes up for the lack of acetylcholine the person had.

    Give two reasons why there was a high frequency of the gene (2 marks)

    Why was the gene not removed by natural selection? (2 marks)
    Carriers of the allele reproduce before age 49 so the gene would be passed on regardless of mutation, no selection pressure against it. It was advantageous for another characteristic previously

    Why was the mutation expressed at different ages? (2 marks)
    Variance in lifestyle/environment leads to variance in epigenetic gene expression/levels of methylation therefore gene expression, and/or variance in genome of individuals may lead to predisposition against the disease in other ways so clinical signs appear later or earlier.

    Why double the sample size and why only 74 of 75 mutations were said to be under threat of developing the disease? (2 marks)
    Two alleles of each gene both susceptible to mutation, and because one individual carried a second mutation which undid the initial mutation in some way/ counteracted it's effect/epistatically silenced the expression of the mutation.
    OR someone else said - 74/2=37, so 37 people were homozygous for the allele and one person was heterozygous. (but this relies on the gene being recessive

    Why test the whole genome and not use a probe to test for the GAC mutation? (2 marks)
    Because the GAC triplet will not be unique to the mutated allele and a probe for that triplet would bind all over the place.




    Offline

    4
    ReputationRep:
    (Original post by Amefish)
    This thread is for paper 2! There have been a lot of people asking for this thread, and of course I'm delivering! Like before, I don't really remember many of the questions so I'm calling all Biology students to contribute whatever they can to help us all out!

    Like before, press the "show" button below to see what we've already got!

    Spoiler:
    Show



    Running causes an increase in heart rate. Describe the role of receptors and the nervous system in this process (~5 marks)
    Chemoreceptors detect the increased CO2 in the blood, sending a signal to the medulla oblongata which sends an impulse down the sympathetic neurone in the autonomic nervous system. When it reaches the sinoatrial node, it secretes noradrenaline which causes impulses to occur more rapidly, increasing the heart rate.


    I talked about the chemoreceptors detecting a decrease in O2 (as it is used in aerobic respiration)- would that also get the marks?
    Offline

    2
    ReputationRep:
    (Original post by Amefish)
    This thread is for paper 2! There have been a lot of people asking for this thread, and of course I'm delivering! Like before, I don't really remember many of the questions so I'm calling all Biology students to contribute whatever they can to help us all out!

    Like before, press the "show" button below to see what we've already got!

    Spoiler:
    Show



    Running causes an increase in heart rate. Describe the role of receptors and the nervous system in this process (~5 marks)
    Chemoreceptors detect the increased CO2 in the blood, sending a signal to the medulla oblongata which sends an impulse down the sympathetic neurone in the autonomic nervous system. When it reaches the sinoatrial node, it secretes noradrenaline which causes impulses to occur more rapidly, increasing the heart rate.


    q.1 (4 marks) Running causes an increase in heart rate. Describe the role of receptors and the nervous system in this process

    *Increased Muscle Respiration
    *Higher conc CO2 in blood
    *Chemoreceptor in cartoid artery detects this
    *Nervous impulse to Sympathetic nervous system in Medulla Oblongata
    *Increased frequency of nervous impulses to SAN
    *Higher frequency of waves of excitation released
    *Higher Heart rate


    The Transgenic Mosquito one was:

    *Add more to population as offspring die before reproducing, so to prevent population size increasing as allele becomes extinct b/c not passed on, external supply of allele is provided in the form of transgenic mosquitos.

    The 74/75 one was:

    One was young, AD was not yet onset - thus not yet potential AD.
    Offline

    2
    ReputationRep:
    Population one was:

    ((1*2*60*24*365.5)/5400000) * 100 = 19.5%
    Offline

    4
    ReputationRep:
    Hardy Weinberg was 32%

    AMPK allows fatty acids into mitochondria to be used as a respiratory substrate

    Sympatric speciation, either different flowering times lead to genetic drift, or extra chromosome during reproduction leads to speciation

    PCR stopped because it ran out of nucleotides

    The diagram with certain genes inhibiting others (white>yellow>green) was an example of epistasis
    Offline

    4
    ReputationRep:
    Phenotype ratio for white : green : yellow was 2 : 1 : 1
    Offline

    1
    ReputationRep:
    it gave you the actual diameter of your field of view and said there were on average (12?) cells per field of view and then you had to calculate the average diameter of one cell
    i got 84um but who knows lol
    Offline

    11
    ReputationRep:
    (Original post by Synesthesia)
    Population one was:

    ((1*2*60*24*365.5)/5400000) * 100 = 19.5%

    I was so worried!! That's what I got but then everyone said something different at school lol
    Offline

    4
    ReputationRep:
    (Original post by saltatrixi1999)
    it gave you the actual diameter of your field of view and said there were on average (12?) cells per field of view and then you had to calculate the average diameter of one cell
    i got 84um but who knows lol
    I think I got that too
    Offline

    1
    ReputationRep:
    (Original post by d010534)
    I was so worried!! That's what I got but then everyone said something different at school lol
    i also got 19.5 !!
    Offline

    2
    ReputationRep:
    (Original post by SK20)
    I think I got that too
    It was 84.10

    (Area)/Pi = R^2

    sqrt(r^2) = r

    r*2 = d

    d/15 = mean

    mean (mm to um) * 1000 = 84.10
    Offline

    4
    ReputationRep:
    (Original post by Synesthesia)
    It was 84.10

    (Area)/Pi = R^2

    sqrt(r^2) = r

    r*2 = d

    d/15 = mean

    mean (mm to um) * 1000 = 84.10
    Yesss that looks familiar
    Offline

    3
    ReputationRep:
    blud i got the first one wrong ffs, i said acetylcholine, parasympathetic neurone ffs
    Offline

    2
    ReputationRep:
    Sympatric - Reproductively seperated in same ecosystem (Ecological Immobility)

    * No gene flow between populations
    * Mutation occurs
    * Increases chance of survival to reproduce
    * Offspring with beneficial allele produced, differential reproductive success continues
    * Allele frequency increases
    * This mutation occurred in both populations
    * Populations diverge to the point of being different species as allele frequnecy changes
    Offline

    4
    ReputationRep:
    predictions for paper 3?
    Offline

    4
    ReputationRep:
    (Original post by mstrcvk)
    Hardy Weinberg was 32%

    AMPK allows fatty acids into mitochondria to be used as a respiratory substrate

    Sympatric speciation, either different flowering times lead to genetic drift, or extra chromosome during reproduction leads to speciation

    PCR stopped because it ran out of nucleotides

    The diagram with certain genes inhibiting others (white>yellow>green) was an example of epistasis

    would i have got the mark for putting dominant epistasis?
    Offline

    2
    ReputationRep:
    (Original post by joshcurtis1999)
    would i have got the mark for putting dominant epistasis?
    They mark using the list principle so it's a toss up.

    Edit: Probably not - the first inhibition was by passive alleles.
    Offline

    4
    ReputationRep:
    (Original post by saltatrixi1999)
    it gave you the actual diameter of your field of view and said there were on average (12?) cells per field of view and then you had to calculate the average diameter of one cell
    i got 84um but who knows lol
    yeh i got 84 aswell
    Offline

    1
    ReputationRep:
    (Original post by SK20)
    I think I got that too
    was 15 and i got 83.3 micrometers
    Offline

    4
    ReputationRep:
    For the iPS cells in mice evaluate the effectiveness in human I talked about how the transplant was successful in mice as after the first week there was similar blood glucose levels to non diabetics however for mice it showed more fluctuations than the non diabetic group. However since it was done in mice, although mice are mammals like humans, there are possible unknown side effects in humans or the treatment may not be effective in human as the transplant cells may be rejected by the immune system and the long term effects are not known in humans so further tests needed.

    For the why the pancreas transplant shouldnt be used for type II diabetes I said type II can be treated with regular exercise and diet so no need to risk surgery. Other point was that in type II the beta cells still produce insulin but insulin receptors are damaged so would be ineffective
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: March 18, 2018

University open days

  • University of the West of England, Bristol
    Undergraduate Open Afternoon - Frenchay Campus Undergraduate
    Wed, 23 Jan '19
  • University of East London
    Postgraduate Open Evening Postgraduate
    Wed, 23 Jan '19
  • University of Gloucestershire
    School of Education Open Day Postgraduate
    Wed, 23 Jan '19
Poll
Brexit: Given the chance now, would you vote leave or remain?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.