DP Biology (first assessment 2025)

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Question 22M.2.SL.TZ2.b

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Date May 2022 Marks available [Maximum mark: 7] Reference code 22M.2.SL.TZ2.b
Level SL Paper 2 Time zone TZ2
Command term Explain Question number b Adapted from N/A
b.
[Maximum mark: 7]
22M.2.SL.TZ2.b

Explain how natural selection can cause traits such as drought resistance to develop in wild plants.

[7]

Markscheme
  1. (natural selection occurs if) there is variation in degree of drought resistance among members of a population/same species;
  2. variation is caused by mutations (when changes occur in the DNA/nucleic bases/chromosomes);
  3. variation during meiosis occurs (with separation of chromosomes);
  4. variation occurs during sexual reproduction (as different alleles combine);
  5. some variations make some plants more drought-resistant;
  6. example of variations: deeper roots/more storage tissue for water/thicker cuticles/less opening of stomata/other verifiable variations;
  7. these variations let some survive and reproduce better/have more offspring
    OR
    (these variations) confer selective advantage;
  8. these variations/characteristics are passed onto offspring which survive better;
  9. natural selection increases the frequency of these characteristics;
  10. eventually leads to changes/evolution in the species / more drought-resistant plants;
Examiners report

The inclusion of ‘drought resistance’ in the stem of the question should have been a suggestion to include it, but many answers were far to general with a vague attempt to explain Natural Selection in general without explaining how the initial variation in the population came about. There were quite a few ‘Lamarckian’ answers with claims of individuals adapting to cope with the change. The average for this question was only 2.8, putting it as one of the most poorly answered.

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