DP Biology (first assessment 2025)

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Question SPM.2.SL.TZ0.7

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Date May Specimen-2023 Marks available [Maximum mark: 15] Reference code SPM.2.SL.TZ0.7
Level SL Paper 2 Time zone TZ0
Command term Explain, Outline Question number 7 Adapted from N/A
7.
[Maximum mark: 15]
SPM.2.SL.TZ0.7

Mutations have a range of consequences for organisms.

(a)

Outline how mutation can lead to cancer.

[4]

Markscheme
  1.  mutations are random changes in the sequences of genes/DNA;
  2.  (mutation) may involve addition/deletion/substitution/inversion of DNA bases;
  3.  (mutations) in tumour suppressor genes/oncogenes;
  4.  uncontrolled cell division/mitosis occurs;
  5.  abnormal cells cannot perform their function;
  6.  they divide repeatedly to form tumours;
(b)

Outline one example of a human disease caused by an autosomal recessive allele.

[4]

Markscheme
  1.  name of condition e.g. PKU / other example;
  2.  mutation in the gene for (the enzyme) phenylalanine hydroxylase (PAH) / if other example used name of gene that is mutated;
  3.  outline of inheritance pattern, e.g. both parents need to carry the recessive allele;
  4.  (without dietary modification, result is) toxic build-up of phenylalanine in the blood / low levels of tyrosine / symptoms if other example used;
  5.  phenylalanine is not converted to tyrosine (by the enzyme) / effect of the mutation on the protein/enzyme/metabolism if other example used;
  6.  requires dietary modification (as treatment) / treatment for other example used;
(c)

Explain the role of mutations in evolution.

[7]

Markscheme
  1.  new phenotypes/traits may result from mutations;
  2.  mutations increase variation/differences between individuals in a population/species;
  3.  individuals with new phenotype/trait may have more chances of survival;
  4.  (more chances of survival) in a changing environment / presence of selection pressures;
  5.  (selection pressure can be) intraspecific competition/abiotic factor;
  6.  natural selection occurs;
  7.  individuals with (advantageous) mutation have longer life spans/live longer;
  8.  (so) more chances of reproduction;
  9.  mutated gene passed on to new generations;
  10.  allele frequencies change in the population over time;
  11.  evolution is a consequence of natural selection;

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