Question 23M.2.SL.TZ2.b
| Date | May 2023 | Marks available | [Maximum mark: 2] | Reference code | 23M.2.SL.TZ2.b |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Deduce | Question number | b | Adapted from | N/A |
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.]
Deduce, giving reasons, which brown pelican population decreased the most in the years following the study.
[2]
- California, as most eggs have a high level of DDE / most eggshells are thinning;
- (California as) less chicks hatching (results in smaller population size)
OR
(California as) birth rate less than death rate (so decrease in population);
