Biology 9700/43 October/November 2025: question paper and mark scheme

Question

Guinea pigs, Cavia porcellus, vary in the length and colour of their fur. Fig. 1.1 shows a guinea pig with short black fur. Fig. 1.1 Two genes that determine the length and colour of the fur occur at the A/a locus and the B/b locus. These two gene loci are on separate autosomal chromosomes. • The allele A results in short fur. • The allele a results in long fur. • A is dominant to a. • The allele B results in black fur. • The allele b results in chocolate fur. • B is dominant to b. (a) (i) List all the possible genotypes of a guinea pig with short black fur. …… [2] (ii) A test cross could be used to determine the genotype of a female guinea pig with short black fur. Describe the phenotype of the male guinea pig that could be used to carry out this test cross. …… [1] * 0000800000003 * DFD 3 (b) A black guinea pig with long fur that was homozygous at both loci was crossed with a chocolate guinea pig with short fur that was homozygous at both loci. The F1 offspring of this cross had short black fur. F1 offspring were mated together to produce the F2 offspring. Complete the Punnett square to: • show the cross between the F1 offspring • predict the F2 offspring genotypes. You should include the gametes in your answer. State the ratio of F2 offspring phenotypes. You should include a key to link phenotypes to genotypes. ratio of F2 offspring phenotypes: [4] (c) Some genes in guinea pigs are structural genes and some are regulatory genes. Describe the difference between a structural gene and a regulatory gene. …… [2] [Total: 9] * 0000800000004 * DFD 4

Question

Exserohilum turcicum is a fungal pathogen. The growth of the mycelium of the fungus damages the leaves of maize plants, Zea mays. Leaf damage reduces crop yield. (a) (i) Complete Table 2.1 to show one structural difference and one functional difference between E. turcicum and Z. mays. Table 2.1 E. turcicum Z. mays structural difference functional difference [2] (ii) Describe the principles by which organisms such as E. turcicum and Z. mays are classified in the taxonomic hierarchy. …… [4] * 0000800000005 * DFD 5 (b) Two inbred varieties of maize, SKV50 and CML153, were crossed. The resulting F1 hybrids were self‑crossed to produce F2 offspring. The F2 plants were grown, and the percentage area of leaf damage caused by E. turcicum was measured. Fig. 2.1 shows the results for the F2 generation. The arrows show the mean percentage area of leaf damage for the two parent varieties. 50 40 30 number of plants 20 10 0 20 30 40 50 60 percentage area of SKV50 leaf damage CML153 Fig. 2.1 (i) Explain how Fig. 2.1 can be used to determine which parent maize variety shows the greatest resistance to infection by E. turcicum. …… [2] (ii) State the name of the type of variation shown by the maize F2 generation in Fig. 2.1. …… [1] (iii) Explain the genetic basis of the type of variation shown by the maize F2 generation. …… [4] [Total: 13] * 0000800000006 * DFD 6

Question

Plants have several different photosynthetic pigments in their chloroplasts. (a) A student separated and identified the chloroplast pigments present in a leaf extract from a spinach plant using two slightly different methods. Method A • A type of chromatography known as thin layer chromatography (TLC) was used to separate the pigments. • A mixture of ether and cyclohexane was used as a solvent in TLC. Method B • The student repeated TLC but treated the spinach leaf extract with a chemical. The chemical causes a magnesium ion in a pigment to be replaced by two hydrogen ions. • The student used a leaf from the same spinach plant, and used the same solvent as in method A. The student calculated Rf values and compared these to reference values to identify the pigments. Fig. 3.1 shows the results for method A and method B. solvent front β-carotene solvent front β-carotene phaeophytin a chlorophyll a phaeophytin b chlorophyll b chlorophyll b xanthophyll xanthophyll line of origin line of origin A B Fig. 3.1 * 0000800000007 * DFD 7 (i) Calculate the Rf value of β‑carotene in Fig. 3.1. Rf = …… [2] (ii) Suggest two explanations for the differences in appearance of chromatograms A and B in Fig. 3.1. 1 …… 2 …… [2] (iii) The student found some different Rf values for the chloroplast pigments of spinach in a scientific paper. The values in the scientific paper were different from the reference values that the student originally used to identify the pigments on chromatograms A and B in Fig. 3.1. Suggest one reason, other than measurement error, for the different Rf values. …… [1] * 0000800000008 * DFD 8 (b) Fig. 3.2 shows the absorption spectra of some chloroplast pigments. key chlorophyll a chlorophyll b carotenoids (β-carotene and xanthophyll) 90 60 percentage absorption 30 0 400 500 600 700 blue red wavelength of light / nm Fig. 3.2 Use Fig. 3.2 to compare the similarities and differences between the absorption spectra of chlorophyll a and carotenoids. …… [4] * 0000800000009 * DFD 9 (c) In some species of plant, the absorption of light stimulates seed germination. The absorption of light increases the production of gibberellin in the embryo of a seed. Describe the role of gibberellin in the germination of a seed. …… [4] [Total: 13] * 0000800000010 * DFD 10

Question

The wolf, Canis lupus, lives in North America. Wolves may have a grey or a black coat colour. The colour of an individual wolf depends on the DNA it inherits at the CPD103 gene locus. • Wolves inherit two copies of CPD103, one from each parent. • Wolves that inherit one copy of the black form of the CPD103 gene have a black coat. (a) State the term used to describe: • an organism that has two copies of each gene …… • a form of a gene …… • a form of a gene that gives a phenotypic effect in a heterozygote. …… [3] In addition to producing black coat colour, the protein coded for by the CPD103 gene also defends against infectious lung disease. Canine distemper virus (CDV) causes serious lung disease in wolves. Wolves that have been previously infected by CDV have antibodies against CDV (anti‑CDV antibodies) in their blood. (b) CDV can be passed from domestic dogs to wolves. • Domestic dogs are more numerous in the southern part of the area occupied by wolves. • Domestic dogs are less numerous in the northern part of the area occupied by wolves. • The relative frequency of black wolves compared to grey wolves increases from the north to the south of the area they occupy. Explain how natural selection causes this trend in the distribution of black wolves. …… [4] * 0000800000011 * DFD 11 (c) Several different populations of wolves were compared. Fig. 4.1 shows the relationship between the percentage of wolves in a population that have anti‑CDV antibodies in their blood and the percentage of wolves in that population that are black. The line of best fit was calculated after comparing the different populations of wolves. 60 50 40 percentage of black wolves 30 in population 20 10 0 0 10 20 30 40 percentage of wolves with anti-CDV antibodies Fig. 4.1 With reference to Fig. 4.1, state the relationship between the percentage of wolves with anti‑CDV antibodies and wolf coat colour, and suggest reasons for this relationship. …… [4] [Total: 11] * 0000800000012 * DFD 12

Question

The endocrine system and the nervous system both coordinate responses in mammals. (a) Complete Table 5.1 to show the features of three cell‑signalling molecules of the endocrine system: antidiuretic hormone (ADH), glucagon and insulin. Use a tick (3) if the molecule has the feature and a cross ( 7) if the molecule does not have the feature. Put a tick (3) or a cross ( 7) in every box. Table 5.1 feature ADH glucagon insulin binds to receptors on cell surface membranes results in molecules moving from cells into the blood is secreted as a result of detection by osmoreceptors [3] (b) The endocrine system has a slower transmission speed than the nervous system. Describe other ways in which the endocrine system and the nervous system differ. …… [4] * 0000800000013 * DFD 13 (c) The endocrine system and the nervous system can affect muscle function. Fig. 5.1 shows a transmission electron micrograph of a longitudinal section of striated muscle tissue that is in a relaxed state. B C D E Fig. 5.1 (i) State the letter on Fig. 5.1 that indicates the length of a sarcomere. …… [1] (ii) State the letter on Fig. 5.1 that indicates a region where actin and myosin overlap. …… [1] (iii) Describe and explain how the region labelled D on Fig. 5.1 changes during muscle contraction. …… [4] [Total: 13] * 0000800000014 * DFD 14

Question

The distribution of the large blue butterfly, Phengaris arion, extends across Europe and Asia. It is assessed by the International Union for Conservation of Nature (IUCN) on the Red List™ as ‘Near Threatened’ globally and ‘Endangered’ in Europe. In Europe, P. arion became extinct in the Netherlands in 1964 and in the United Kingdom in 1979. Fig. 6.1 lists the conservation status categories in the IUCN Red List™. conservation status Extinct (EX) Extinct in the Wild (EW) Critically Endangered (CR) Endangered (EN) increasing risk of extinction Vulnerable (VU) Near Threatened (NT) Least Concern (LC) Fig. 6.1 Fig. 6.2 shows P. arion. Fig. 6.2 (a) (i) Explain how IUCN Red List™ assessments help to conserve biodiversity. [3] * 0000800000015 * DFD 15 (ii) With reference to Fig. 6.1 and the IUCN assessments for P. arion, suggest how the abundance of the butterfly differs across its distribution. …… [2] (b) P. arion has been successfully re‑introduced in the United Kingdom at 12 sites. These sites were restored to flower‑rich grassland. The conservation management actions designed for P. arion also resulted in the re‑establishment or increase of other species at the restored sites. These included 12 species of flowering plant, 8 other butterfly species and 4 species of other insects. (i) Use the information given to suggest why P. arion went extinct in the United Kingdom in 1979. …… [2] (ii) Outline the advantages of restoring habitats for endangered species. …… [4] [Total: 11] * 0000800000016 * DFD 16

Question

In aerobic respiration, most ATP is produced by oxidative phosphorylation. (a) Outline the features of ATP that make it suitable as the universal energy currency. …… [3] (b) Rotenone is a compound that affects oxidative phosphorylation. Rotenone disrupts the first carrier in the electron transport chain by stopping the transfer of electrons from this carrier. Suggest and explain how rotenone reduces the production of ATP and water in aerobic respiration. …… [6] [Total: 9] * 0000800000017 * DFD 17

Question

LibertyLink® soybean is a genetically modified crop. It was first grown in 1996 and used in food products from 1998. It has been grown in 6 countries and used in food products in 21 countries. Table 8.1 summarises the modifications made to the soybean plant to produce LibertyLink® soybean. Table 8.1 name of introduced gene donor organism gene product function of gene product gene Streptomyces phosphinothricin stops action of glufosinate, pat viridochromogenes N‑acetyltransferase a herbicide (a) Explain how the modification made to produce LibertyLink® soybean may help to solve the global demand for food. …… [4] (b) (i) Name the type of enzyme that could be used to cut out the pat gene from S. viridochromogenes. …… [1] (ii) Name the enzyme that could be used to join the pat gene to a plasmid by forming phosphodiester bonds. …… [1] (c) Suggest reasons why LibertyLink® soybean is used in food products in 21 countries but only grown in 6 countries. …… [3] [Total: 9] * 0000800000018 * DFD 18

Question

(a) Fig. 9.1 shows a longitudinal section of a human kidney. X Y Fig. 9.1 Name the regions of the kidney labelled X and Y in Fig. 9.1. X …… Y …… [2] (b) A biosensor can be used to measure the concentration of glucose in urine. Outline how a biosensor measures the concentration of glucose in urine. …… [4] [Total: 6] * 0000800000019 * DFD 19

Question

Explain the relationship between genes, proteins and phenotype, with reference to two examples of genetic diseases in humans. …… [6] * 0000800000020 * DFD 20 The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries.