DP Biology (last assessment 2024)

Test builder »

Question 23M.3.HL.TZ2.21

Select a Test
Date May 2023 Marks available [Maximum mark: 6] Reference code 23M.3.HL.TZ2.21
Level HL Paper 3 Time zone TZ2
Command term Explain Question number 21 Adapted from N/A
21.
[Maximum mark: 6]
23M.3.HL.TZ2.21

Explain how biogeographic factors affect the richness and evenness of biodiversity.

[6]

Markscheme
  1. biogeographic features are combinations of species, habitats and physical features;
  2. richness is the number of different species present (in an area);
  3. evenness refers to relative abundance of the different species (in an area) /OWTTE;
  4. large nature reserves/large islands (potentially) have greater biodiversity /richness / evenness;
  5. large areas (tend to) have more species/populations/habitats/richness
    OR
    large areas have more stability/higher biodiversity index
    OR
    have less chances of loss of a species;
  6. connected areas/nature reserves have more diversity than isolated ones
    OR
    corridors between (small) areas/ reserves increases richness/biodiversity;
  7. the greater the surface:perimeter ratio, the greater the biodiversity;
  8. edges are transition areas
    OR
    have greater richness/lower evenness
    OR
    are less stable;
  9. circular shape has more biodiversity than rectangular shape;
  10. biodiversity measured by Simpson’s / diversity index;
  11. one additional abiotic factor affecting biodiversity;

 e.g. precipitation, soil quality/content, temperature, etc.

Examiners report

A large number of candidates had difficulty with this question in spite of the Biology Guide (C.4) being quite explicit in terms of biodiversity, richness, evenness, size and edge effects. Many were unable to structure their answer and wrote about limiting factors in generalised ways for biomes, relationships between species, habitats, niches, evolution, nutrients, minerals, abiotic/biotic factors, climate, temperature and predation. There were nevertheless a few candidates who had learnt this topic well and provided complete answers in the expected terms without any irrelevant material.

Syllabus sections