Question 18N.3.HL.TZ0.14
| Date | November 2018 | Marks available | [Maximum mark: 6] | Reference code | 18N.3.HL.TZ0.14 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Identify, Outline, State, Suggest | Question number | 14 | Adapted from | N/A |
An investigation into food web interactions was conducted in mesocosms in the Mediterranean Sea, off the coast of France. The effects of the addition of soil and fish on bacterial populations were tested.
Each of the mesocosms is an open ecosystem. State the property that makes the mesocosms open ecosystems.
[1]
there is exchange of matter/energy
OR
there is an exchange between the surface of the water and the atmosphere ✔
eg: matter could be nutrients/gas/water/minerals/etc; energy could be heat or light
Assuming that the populations of bacteria are under bottom-up control, identify the mesocosms in which the bacterial populations will be highest.
[1]
soil and no fish «mesocosm» AND soil and fish «mesocosm» ✔
Both mesocosms required
Accept answers such as “the two with soil”.
Outline top-down effects on the bacteria in the four mesocosms.
[2]
a. zooplankton feed on bacteria reducing their numbers ✔
b. fish feed on zooplankton «therefore» increasing bacterial population ✔
Suggest advantages of undertaking this experiment in the sea rather than in the laboratory.
[2]
a. conditions closer to levels experienced naturally by the organism ✔
OWTTE
b. natural variation of abiotic variables ✔
Accept examples, eg: temperature, dissolved oxygen
c. more natural behaviour/interactions ✔
d. not harm organisms by removing them from natural habitat ✔