DP Biology (first assessment 2025)

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Question 22M.2.SL.TZ1.8c

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Date May 2022 Marks available [Maximum mark: 7] Reference code 22M.2.SL.TZ1.8c
Level SL Paper 2 Time zone TZ1
Command term Explain Question number c Adapted from N/A
c.
[Maximum mark: 7]
22M.2.SL.TZ1.8c
(c)

Explain the reasons for variation in human height.

[7]

Markscheme
  1. environment affects height;
  2. nutrition/malnutrition affects growth rate / other example of environmental factor affecting height;
  3. genes/alleles affect height / height is partly heritable;
  4. polygenic / many genes influence height;
  5. continuous variation;
  6. normal/bell-shaped distribution of height;
  7. some alleles (of these genes) increase height and some reduce it;
  8. many possible combinations of alleles of these genes;
  9. specific gene mutations/alleles cause dwarfism/extreme height;
  10. meiosis generates variation (in height);
  11. mutations generate variation (in height);
  12. males tend to be/are on average taller than females;
  13. loss of height during aging;
Examiners report

This was a relatively high scoring question, with a mean mark of 2.4 (out of 7). Teachers expressed surprise in G2 forms that their students were being expected to make 7 valid points in their answer, but the wide-ranging mark scheme ensured that this was possible. There was some confusion between polygenic inheritance and multiple alleles. Weaker candidates tended to think that dominant alleles make us taller and recessive alleles cause shortness. Another fault in many answers was to focus on natural selection and evolution of height — if anything natural selection will reduce variation in human height rather than cause it.

Syllabus sections