| Date | May 2019 | Marks available | 2 | Reference code | 19M.1.SL.TZ0.5 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Suggest | Question number | 5 | Adapted from | N/A |
Question
Figure 4(d): Example of a Coral Triangle marine food web
With reference to Figure 4(d), suggest the impact on the marine food web if tuna numbers were to decline.
Markscheme
reduction in sharks/marlin (predators) of the tuna (due to reduction in food source);
increase in micronekton/predatory fish (prey) of the tuna (due to reduction in predation);
reduction in phytoplankton/mesoplankton/microplankton due to increase in micronekton population;
loss of tuna reduces competition for food (micronekton/predatory fish) resulting in overall increase in sharks/marlin population;
to compensate for loss of tuna, shark/marlin eat more micronekton/predatory fish resulting in overall decline of micronekton/predatory fish population;
to compensate for loss of tuna, shark/marlin eat more micronekton/predatory fish resulting in an increase in phytoplankton/mesozooplankton/microzooplankton population;
Accept other reasonable responses.
Do not credit the same marking point twice eg reduction in sharks and reduction in marlin.
Do not accept only “collapse of marine food web” or “reduction in biodiversity”.
[2 max]
Examiners report
This question was answered well by most candidates. Common errors included: (i) only stating changes in feeding behaviour but not how this affects the population numbers; (ii) misinterpreting the direction of the errors.
