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9477 Specimen Paper 2 Answers

The batch of students taking the A Level examinations in 2026 will be the first cohort to tackle the challenging 9477 paper. With the newly released Specimen Paper 2, we are the first tuition centre to release the accurate Cambridge mark scheme before other schools even do!

Question 1 (9 marks)

(a) State the names of the organelles labelled C and D in Figure 1.1. [2]

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  • C = Golgi body / apparatus / complex ; (R: golgi)

  • D = secretory / exocytic, vesicle ; (R: lysosome)

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(b) Explain the detection of radioactivity at different times in the organelles labelled A and B. [4]

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  • protein synthesis using labelled amino acids ;

  • ref. to ribosomes on RER ; (R: mention of A and B without identification)

  • ref. to passing of, polypeptide / protein, through RER membrane ;

  • ref. to transport of, polypeptide / protein, within cisternae of RER / polypeptide enter the lumen of RER for folding and packaging into vesicles ;

  • ref. to vesicles, pinch / bud, off from RER ; (ignore description beyond B)

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(c) Describe how the material in the organelle labelled D passes out of the cell. [3]

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  • through the process of exocytosis ;

  • movement of vesicles to the cell surface membrane ;

  • fusion of membrane of vesicle with cell surface membrane ;

  • thus, emptying vesicle contents / release material into extracellular region ;

  • AVP ; e.g. ref. to role of, microtubules / cytoskeleton / kinesin, in vesicle movement

Question 2 (8 marks)

(a) Explain the effect of increasing temperature on the quantity of product formed after one hour. [4]

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  • increase in kinetic energy ;

  • increase frequency of collisions ;

  • increase, enzyme-substrate/ES, complex formation ;

  • up to optimum ;

  • then denatured ;

  • ref. to breaking of H bonds/loss of 3-D structure/change in active site ;

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(b) Explain the change in the optimum temperature of the reaction as the time increases from one hour to five hours. [2]

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  • ref. to more, denaturation/AW, as more time spent at high temperature ;

  • reducing (effective) concentration of enzyme ;

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(c) Explain why, at high substrate concentrations, an increase in substrate concentration does not increase the initial rate of reaction. [2]

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  • (all available) active sites occupied (at any one time) ; 

  • substrate no longer limiting/in excess ;

  • ref. to saturation/max reaction rate ;

  • enzyme concentration limiting ;

Question 3 (12 marks)

(a) Explain how the mutation shown in Figure 3.1 may change the structure and function of the ras protein. [3]

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  • change â€‹in amino acid / gly for val ;

  • change in 3D conformation / folding of protein / tertiary structure ;

  • ref. to change, bonding / R group / hydrophobic interactions / hydrogen bonding ;

  • ref. to changes, binding / interaction of protein with other molecules or is non-functional ;

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(b) Describe the differences between these two types of mutation. [2]

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  • single vs 2 mutations needed for effect on phenotype ;

  • dominant vs recessive allele made ; 

  • activate vs inactivate a process ;

  • oncogene vs tumour suppressor gene ;

​​​

(c) State two factors that can cause mutations. [2]

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  • (ionising) radiation / correct e.g. ; 

  • carcinogen / correct e.g. ;

  • virus / correct e.g. ;

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(d) Using the details provided in Figure 3.1 and Figure 3.2, describe how this mutation of the c-myc proto-oncogene to an oncogene differs from the mutation of the H-ras proto-oncogene to an oncogene. [2]

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  • is a chromosome mutation / translocation, not a gene mutation ;

  • involves transfer of whole genes / c-myc not just base change ;

  • changes control of expression / regulation, not the protein produced ;

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(e) With reference to Figure 3.3, describe differences between the effects of c-myc, H-ras and a combination of c-myc and H-ras in causing tumours in mice. [3]

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  • c-myc longer time / slower / >100 days vs H-ras shorter time / faster / 15-25 days for first appearance of tumour

  • c-myc fewer mice develop tumours / 30-40% have tumours vs H-ras more mice develop tumours / 55-65% have tumours 

  • combined more mice develop tumours / all have tumours before 200 days / after 180 days / by end of study ;

  • combined more rapid onset ;

Question 4 (11 marks)

(a) Draw a genetic diagram in the space provided to show the genotype of the isolated maize plant and how self-pollination of this maize plant could produce the expected phenotypic ratio of grains. [4]

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  • correct parental genotype AaBb ;

  • correct parental gametes AB Ab aB ab ;

  • correct Punnett square ;

  • correct genotypic and phenotypic ratio of 9:3:3:1 ;

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(b) Using your genetic diagram from (a), calculate the percentage of the purple, smooth grains that would be expected to grow into true breeding maize plants. [1]

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  • 6.25% ;

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(c)(i) Complete the expected number (E) for each of the four phenotypes in column 4 [1]

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  • 213.75, 71.25, 71.25, 23.75 ; (A: 3.sf.)

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(c)(ii) Complete the two missing values for yellow, smooth grains and yellow, shrunken grains in column 5 [1]

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  • 3.71, 2.21 ; 

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(c)(iii) Complete the chi-squared (χ2) value in column 5. [1]

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  • 6.58 ;

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(d) Use your calculated chi-squared value in Table 4.2 and the data in Table 4.3 to conclude whether the observed number of each phenotype is significantly different to the expected number of each phenotype. [3]

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  • there is no significant difference between observed and expected results ;

  • because greater than 0.05 ;

  • ratio phenotype is 9:3:3:1 / inheritance is Mendelian ;

  • observed differences are due to chance ;

Question 5 (7 marks)

(a) State precisely where in the chloroplast RuBP and PGA are synthesised. [1]

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  • stroma ;

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(b) Explain why the concentration of RuBP changed between 200 seconds and 275 seconds. [2]

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  • lower, carbon dioxide/CO2, concentration ;

  • less carbon fixation / less RuBP converted to PGA / less, carbon dioxide/CO2 combining with RuBP ;

  • RuBP continues to be reformed from GP / TP ;

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(c) Calculate the mean rate of decrease in the concentration of PGA between 200 seconds and 350 seconds. [2]

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  • 1.8/150 or (2.0-0.2)/150 or (2.0-0.2)/(350-200) ;

  • 0.012 ;

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(d) Explain how the decrease in the concentration of PGA leads to a decreased harvest for commercial suppliers of Chlorella. [2]

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  • less GP / TP ;

  • (so less) conversion to, (other) carbohydrates / lipids / amino acids / proteins ; (A: named examples, e.g. glucose / hexose / cellulose / starch)

  • AVP ; e.g. (amino acids) used to make proteins for growth / cell division, (carbohydrate / lipid) for respiration for, growth / cell division​

Question 6 (11 marks)

(a)(i) identify the two stages of mitosis shown [2]

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  • metaphase ;

  • anaphase ;

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(a)(ii) describe what happens to sister chromatids after 15 minutes. [2]

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  • centromeres split / divide / chromatids, separate ;

  • chromatids become chromosomes ;

  • pulled apart by spindle fibres / microtubules ;

  • (pulled) towards, poles (of spindle) / asters / centrioles ;

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(b) Outline the roles of centromeres. [3]

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  • allow sister chromatid adhesion ;

  • divide at start of anaphase in mitosis ;

  • ref. to kinetochore (formation) / proteins which bind on the centromeres ;

  • ref. to spinlde attachment ;

  • required for chromatid alignment / separation ;

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(c) State four ways in which the behaviour of chromosomes in meiosis is different from their behaviour in mitosis. [4]

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  • homologous chromosomes, pair up / form bivalents / undergo synapsis vs homologous chromosomes do not pair up ;

  • crossing over / chiasmata formation vs no, crossing over / chiasmata formation ;

  • homologous chromosomes / bivalent, line up at equator vs single chromosomes line up at equator

  • homologous chromosomes separate in anaphase I vs (sister) chromatids separate in anaphase ;

  • reduction in chromosome numbers / halves chromosome number / results in haploid cells vs no reduction in number of chromosomes / results in same number of chromosomes / diploid number maintained ;

Question 7 (11 marks)

(a) Describe the role of NAD in cellular respiration. [3]

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  • coenzyme ;

  • carries (high energy) electrons and protons ;

  • to electron transport chain ;

  • ref. to reversible / regeneration / redox ;

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(b) Explain why NAD cannot be regenerated from reduced NAD in mitochondria in the absence of oxygen. [3]

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  • oxygen required to accept electrons / oxygen forms water with electrons and protons at end of chain ;

  • in absence of oxygen, electron transfer chain does not work ;

  • first step in ETC (NADH dehydrogenase) removes electron and proton from NADH+ ;

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(c)(i) Explain how the proton gradient that drives ATP synthesis is produced. [3]

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  • ref. to NADH / FADH ;

  • flow of electrons through ETC / ETS / hydrogen carrier system ;

  • ref. to conformational change in ETC ;

  • pumping of protons across membrane / into intermembrane space ;

  • membrane impermeable to protons ;

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(c)(ii) With reference to Figure 7.1, outline how the proton gradient drives ATP synthesis. [3]

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  • protons, diffuse / pass, down concentration gradient ;

  • ref. to rotation of ATP synthase ;

  • ref. to ADP and Pi ;

Question 8 (13 marks)

(a) Suggest how repeated changes in climate between the warm phase and cool phase shown in Figure 8.1 may lead to the evolution of new species and greater species diversity. [5]

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  • (in warm phase) geographical isolation ;

  • reduced / no gene flow / interbreeding ;

  • different conditions / different selection pressures ;

  • allopatric speciation ;

  • (in cool phase) ref. to spread of new species ;

  • previously isolated populations came back into contact but can no longer interbreed ;

  • ref. to effect of repeated rounds of speciation / fragmentation ;

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(b) State one anthropogenic activity that indirectly contributes to increases in greenhouse gases in the atmosphere and explain how the activity results in these increases. [2]

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  • clearing of forests ;

  • less trees to photosynthesise / store carbon ;

  • increasing consumption of meat ;

  • more rumination from cattle ;

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(c)(i) Suggest why the carbon footprint in Table 8.1 is measured in terms of an equivalent mass of carbon dioxide. [2]

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  • carbon dioxide/CO2 is the most abundant / common form of greenhouse gas ;

  • ref. to standard / universal metric to quantify the greenhouse emission levels ;

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(c)(ii) Explain why bioethanol has a much lower carbon footprint than oil, coal and gas. [2]

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  • sugarcane / plants, absorb CO2 during photosynthesis ;

  • thus overall net emissions is lower as CO2 released in combustion is offset ;

  • ref. to carbon neutrality ;

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(c)(iii) State two reasons why wind power and hydroelectric power have carbon footprints that are greater than zero. [2]

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  • creating infrastructural material ;

  • building the machinery to operate ;

  • clearing land for the machinery ;

  • transporting parts over long distances ;

Question 9 (7 marks)

(a) State a named example of each. [2]

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  • antibodies: immunoglobulin (Ig) G ; (A: other named example, IgA/D/E/M)

  • antibiotics: penicillin ; (A: other named example)

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(b) Explain how the size and shape of antibody molecules and antibiotic molecules relate to their modes of action and functions. [5]

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  • ​ref. to both specific ;

  • antibody binds to antigen ;

  • antibody shape complementary to antigen ;

  • antibodies have two antigen-binding sites ;

  • ref. to large size of antibodies since need several binding sites / for interactions with other cells / AW ;

  • antibiotics are enzyme inhibitors ;

  • antibiotic shape complementary to active site of enzyme ;

  • ref. to small size of antibiotics allow them to interfere with enzymes ;

  • antibiotics prevent growth / protein synthesis / cell wall synthesis ;

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