DP Biology (first assessment 2025)

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Question 23M.2.SL.TZ2.18c

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Date May 2023 Marks available [Maximum mark: 3] Reference code 23M.2.SL.TZ2.18c
Level SL Paper 2 Time zone TZ2
Command term Outline Question number c Adapted from N/A
c.
[Maximum mark: 3]
23M.2.SL.TZ2.18c

DDE (dichlorodiphenyldichloroethylene) is formed from the breakdown of DDT (dichlorodiphenyltrichloroethane). In a study done in 1969, eggs of the brown pelican (Pelecanus occidentalis) were collected from colonies in California, South Carolina and Florida, USA. The amount of DDE in each egg was quantified and the percentage of eggshell thinning was measured by comparison with the mean thickness measure before the use of DDT from 1947.

The graph shows the relationship between DDE concentration and eggshell thinning in each of the eggs studied.

[Source: Material from: Blus, L., Gish, C., Belisle, A. and Prouty, R., Logarithmic relationship of DDE residues to eggshell thinning,
published 1972, Nature, reproduced with permission of SNCSC.]

(c)

Outline the biomagnification of DDE in brown pelicans.

[3]

Markscheme
  1. DDE accumulates in (fat tissues of) organisms/bioaccumulation;
  2. (brown) pelicans/birds feed on fish/organisms (that have accumulated DDE);
  3. (DDE) is not excreted;
  4. (DDE) concentration increases as trophic level increases;
  5. (brown) pelicans are in a high trophic level (so have a high accumulation);

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