PAST PAPER 2 Exam Qs

• 2018 Paper 2 Comprehension:

  Red-green colour blindness affects more men than women. Explain why [2 marks]

  1. (Gene/allele) is on the X chromosome (because it is sex-linked) - reference to allele is essential
  2. Females require two alleles/females can be heterozygous/carriers and males require one allele - reference to male and female is required
• One method used to try to reduce transmission of this disease is the Sterile Insect Technique (SIT). This involves releasing large numbers of sterile (infertile) male A. aegypti into the habitat. These males have been made infertile by using radiation.

  Explain how using the SIT could reduce transmission of dengue. [2], 2017

  • MP1: RECOGNISES THAT THIS IS INTRASPECIFIC COMPETITION (7.4 Populations in Ecosystems)
  • Mosquitoes compete (with fertile males) to mate/for food/resources
  • Sterile mosquitoes do not reproduce/breed OR reduces population of mosquitoes
• Describe how the mark-release-recapture method could be used to determine the population of A. aegypti at the start of the investigation. [3 marks]

  • CAPTURE / COLLECT / SAMPLE mosquitoes, mark AND release them back into their habitat
  • Ensure marking is not harmful / affect survival
  • Leave time for mosquitoes/Aedes to disperse before second sampling/collection
  • Population = number in first sample × number in second sample divided by number of marked in second sample/number recaptured;
• The release of radiation-sterilised A. aegypti has not been very successful in controlling the transmission of dengue. Suggest one reason why.

  • Radiation affects their ‘attractiveness’/courtship /survival/ life span
  • Accept: ‘die/less likely to survive due to radiation’.
• Recently a new method was developed to control A. aegypti. Scientists produced transgenic males carrying a ‘lethal gene’ which kills their offspring before they can reproduce.

  Suggest why the scientists released more transgenic males every week. [1 mark]

  • To maintain number/competition as they die/have a short life span
  • To replace mosquitoes that have died.
• The scientists then compared the length of time that the control mice and the trained mice could carry out prolonged exercise. The trained mice were able to exercise for a longer time period than control mice. Explain why. [3 marks]

  1. More aerobic respiration produces more ATP / produces ATP faster
  2. Anaerobic respiration delayed / no anaerobic respiration
  3. Less or no lactate;
• • Tube 1 – 1 cm3 of solution without chloroplasts and 9 cm3 of DCPIP solution in light.

  Explain why the student set up Tube 1. [2 marks]

  1. To show light does not affect DCPIP
  2. To show chloroplasts are required for decolourisation of DCPIP
• The student evaluated the effectiveness of different chemicals as weed-killers by assessing their ability to prevent the decolourisation of DCPIP in chloroplast suspensions.

  The IC50 is the concentration of chemical which inhibits the decolourisation of DCPIP by 50%.

  Explain the advantage of the student using the IC50 in this investigation. [1 mark]

  • MUST QUALIFY YOUR ANSWER
  • Provides a standard / reference point
  • Can compare different chemicals/weedkillers
  • Can compare different concentrations of chemicals/weed-killers;
• Explain why an increase in shoot biomass can be taken as a measurement of net primary productivity. [2 marks]

  1. Represents dry MASS / MASS of CARBON
  2. Represents gross production minus respiratory losses
  3. NPP = GPP - R
• Explain the role of DNA polymerase in RT-PCR. [1 mark]

  • Joins nucleotides to produce complementary strands of DNA
  • NUCLEOTIDES and DNA is underlined in the markscheme.
• Any DNA in the sample is hydrolysed by enzymes before the sample is added to the reaction mixture. (in Reverse transcriptase-PCR) Explain why. [2 marks]

  1. To remove any DNA present - MUST HAVE THE IDEA OF DESTRUCTION / Removal
  2. As this DNA would be amplified/replicated;
• Suggest one reason why DNA replication stops in the polymerase chain reaction. [1 mark]

  • Limited number of primers/nucleotides / 'used up'
  • DNA polymerase (eventually) denatures
• Scientists have used the RT-PCR method to detect the presence of different RNA viruses in patients suffering from respiratory diseases.

  The scientists produced a variety of primers for this procedure. Explain why. [2 marks]

  1. Base sequences differ
  2. Different COMPLEMENTARY primers required;
• Suggest why a DNA probe for the mutated triplet was not considered a suitable method for detection of the E280A mutation (lines 22–23). [2 marks]

  1. (GCA/triplet) is common/found in other places
  2. Would not know if it was the mutation/allele/gene OR Produces ‘false positives'
• There is a positive correlation between the size of snow geese and how far north they breed. A large size results in snow geese being adapted for breeding in colder conditions. Explain how. [2 marks, Jan 10, SIMILAR to black bear comprehension question]

  • Small surface area to volume ratio / more fat
  • Lose less heat (to the environment) / for insulation
  • When they are sitting on eggs;
• Dead leaves contain starch. Describe how microorganisms make carbon in starch available to plants [2 marks]

  • Extracellular digestion / releases enzymes
  • Microorganisms hydrolyse starch to monosaccharides /glucose/sugars/smaller molecules
  • Microorganisms respire product of digestion (the monosaccharides)
  • Produce carbon dioxide from respiration
• Scientists transferred slices of apple from air to anaerobic conditions in pure nitrogen gas. They measured the rate of carbon dioxide production.

  5 (b) The scientists kept the temperature constant throughout the investigation. Explain how a decrease in temperature would affect the rate of carbon dioxide production.

  • Respiratory reactions controlled by enzymes
  • Rate decreases as less kinetic energy/fewer collisions (between substrate and active site) = fewer E-S complexes formed
  • This is a spec link to 1.4.2 Many proteins are enzymes (Synoptic link between 5.2 Respiration and 1.4.2 Enzymes)
• Use this pathway to explain the part played by reduced NAD when the apple slices were transferred to nitrogen. [2 marks]

  • Requires gain of from pyruvic acid hydrogen/electrons / is reduction (USING THE DIAGRAM)
  • These hydrogens comes from reduced NAD/reduced NAD reduces (pyruvic acid) / reduced NAD oxidised

  
• Species X is the first tree to become established in the succession. Use the graph to explain why it is likely to become established earlier in the succession than Y or Z.

  • Vegetation consists mainly of low growing species/herbs/annuals/ no/few trees (Using the diagram)
  • Species X has high rate of photosynthesis at high light intensity
  • Species X grow fastest at high rate of photosynthesis / at high light intensities
  • Will outcompete other species Y/Z;

  
• 6 (b) Species X may change the environment so that it becomes more suitable for species Z. Use the graph to explain why.

  • Produces shade/reduces light intensity - SINCE Species X grows the most
  • Species Z grows best/photosynthesis best/ in low light intensity (USING THE GRAPH)
  • Species Z does not grow well / low rate of photosynthesis in high light intensity (USING THE GRAPH)

  
• Explain why a statistical test was necessary in analysing the results (for the common shrew).

  Use the terms chance and probability in your answer. [2 marks]

  • A statistical test determines the probability of results being due to chance
  • Enables null hypothesis/description of null hypothesis to be accepted/rejected
  • Determines whether correlation/result is significant;
• In the test plot, BARE GROUND was left between the MAIZE and the GRASS species. Suggest an explanation why. [2 marks]

  1. This is referring to something about competition; Model answer:
  2. To prevent competition between the maize and the grass
  3. For light / nutrients / water (Named resource)
• The observed ratio of red-eyed females to red-eyed males was similar to, but not the same as, the expected ratio. Suggest one reason why observed ratios are often not the same as expected ratios.

  • Fertilisation is random / fusion of gametes is random
  • small/not large population/sample /
  • Might have selection advantage/disadvantage SO meaning lethal alleles
• As a result of this investigation, the scientists concluded that more studies on pesticides should be carried out in natural habitats rather than under laboratory conditions. Suggest two advantages of carrying out such investigations in natural habitats.

  1. Can see effect of other biotic factors / effect on other organisms
  2. Can see effect of abiotic factors / named abiotic factor
• The black mamba’s toxin kills prey by preventing their breathing. It does this by inhibiting the enzyme acetylcholinesterase at neuromuscular junctions. Explain how this prevents breathing.

  1. Acetylcholine not broken down / stays bound to receptor;
  2. Na+ ions continue to enter / continued depolarisation / Na+ channels (kept) open / action potentials/impulses fired (continuously)
  3. Intercostal muscles stay CONTRACTED / cannot relax;
• When the sarcomeres contract, what happens to the length of the I-band

  • Decreases

  
• People who have McArdle’s disease produce less ATP than healthy people. As a result, they are not able to maintain strong muscle contraction during exercise. Use your knowledge of the sliding filament theory to suggest why. [3 marks]

  1. This question asks about the role of ATP in muscle contraction - so markscheme: Idea ATP is needed for:
  2. Attachment/cross bridges between actin and myosin
  3. ‘Power stroke’ / movement of myosin heads / pulling of actin
  4. Detachment of myosin heads
  5. Myosin heads move back/to original position / ‘recovery stroke’;
• Scientists investigated the effect of taking omega-3 fatty acids in fish oil on heart rate during exercise. Group B was given capsules containing olive oil. Explain why [1 mark]

  1. To ensure results are due to omega-3/fatty acids (only) / not due to something else in the oil (results are due to independent variable)
  2. Placebo linked to mental/psychological effect;
• Many attempts to produce transgenic animals have failed. Very few live births result from the many embryos that are implanted.

  5 (c) (i) Suggest one reason why very few live births result from the many embryos that are implanted.

  1. Mutation / nucleus/ chromosomes/DNA may be damaged / disrupts genes
  2. May interfere with proteins (produced)/gene expression / translation
  3. Embryo is foreign antigen
  4. So embryo is rejected / attacked by the immune system
• It is important that scientists still report the results from failed attempts to produce transgenic animals. Explain why.

  1. Saves time/money for others
  2. Same work is not repeated / methods can be compared/improved/ amended/ same errors are not made;
• Research workers have suggested that treating diabetes in humans by this method of gene therapy would be better than injecting insulin. Evaluate this suggestion.

  1. Avoids injections / pain of injections
  2. Long(er) lasting / permanent / (new) cells will contain/ express gene
  3. Less need to measure blood sugar / avoids the highs and lows in blood sugar
  4. Less restriction on diet
  5. Rats are different to humans
  6. May have side effects on humans;
  7. Long(er) term effects (of treatment) not known / may have caused effects after 8 months
  8. Substitute insulin may be rejected by the body;
• Use information in the graph to evaluate this suggestion - correlation graph [June 2012, Q8a]

  1. Describe its correlation - Negative correlation
  2. Wide range
  3. Overlap
  4. Graph suggests that OTHER FACTORS may be involved
• Huntington’s disease is always fatal. Despite this, the allele is passed on in human populations. Use information in the graph to suggest why.

  SAME idea as 2017 Comprehension

  1. Age of onset can be high / symptoms appear later in life
  2. So individuals have already had children / allele has been passed on
  3. OR 3. Individuals have passed on the allele / already had children;
  4. Before symptoms occur;
• 6.1.2 Receptors - 2023 Paper 3 Q1.1

  • Refer to stretch-mediated sodium ion channels
  • Refer to sodium IONS
  • Refer to sodium ions DIFFUSING in NOT just influx
• Use Figure 1 to describe what is meant by the all-or-nothing principle.

  • An action potential is only generated/produced when threshold is reached
  • OR An action potential is not generated/produced until/unless threshold is reached;
  • When high pressure was applied (to the fingertip), threshold was reached OR high pressure generates an action potential