DP Biology (last assessment 2024)

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Question 23M.3.SL.TZ1.13

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Date May 2023 Marks available [Maximum mark: 7] Reference code 23M.3.SL.TZ1.13
Level SL Paper 3 Time zone TZ1
Command term Describe, Explain Question number 13 Adapted from N/A
13.
[Maximum mark: 7]
23M.3.SL.TZ1.13

Scientists examined the distribution of lichen species in Seoul, South Korea. The line graph shows the number of lichen species found on the bark of trees in green areas at different distances from the city centre.

[Source: Ahn, C., Chang, E. and Kang, H, 2011. Epiphytic macro lichens in Seoul: 35 years after the first lichen study in Seoul.
Journal of Ecology and Field Biology, [e-journal] 34(4), pp. 381–391. https://doi.org/10.5141/JEFB.2011.040.]

(a)

Describe the trend in the distribution of lichen species.

[1]

Markscheme

lichen species increase as distance from the city centre increases/positive correlation/trend;

Examiners report

The trend was usually described correctly in some way, with some candidates focussing on the points rather than the trend line.

(b)

Explain how lichens can be used as indicator species.

[3]

Markscheme
  1. indicator species live in specific environmental conditions;
  2. absence (of lichens) is an indicator or (air) pollution;
  3. relative numbers of indicator species could be used to calculate biotic index;
  4. biotic index can be used to monitor pollution levels over time;
  5. can help evaluate antipollution actions/measures;
Examiners report

Many candidates mentioned pollution but the term biotic index was rarely seen. Tolerance of some lichens to environmental conditions was occasionally seen.

(c)

Describe a method that can be used to measure the diversity of herbaceous plants in one of the green areas at different distances from the main road.

[3]

Markscheme
  1. lay a line/belt transect line away from the road;
  2. quadrat sampling can be used;
  3. record the number of different species;
  4. count the number of plants in each species;
  5. calculate diversity using the (reciprocal) Simpson’s diversity index;

OWTTE

Accept quadrant

Accept formula for mpe
D=N(N-1)∑n(n-1)

Examiners report

It appeared that few students had undertaken the necessary field work here. Quadrats (usually quadrants) were often mentioned but rarely transects. A few explained Simpson diversity index. The question discriminated well for higher achieving students.