Date | November 2018 | Marks available | 2 | Reference code | 18N.3.HL.TZ0.14 |
Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
Command term | Suggest | Question number | 14 | Adapted from | N/A |
Question
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.
Assuming that the populations of bacteria are under bottom-up control, identify the mesocosms in which the bacterial populations will be highest.
Outline top-down effects on the bacteria in the four mesocosms.
Suggest advantages of undertaking this experiment in the sea rather than in the laboratory.
Markscheme
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
soil and no fish «mesocosm» AND soil and fish «mesocosm» ✔
Both mesocosms required
Accept answers such as “the two with soil”.
a. zooplankton feed on bacteria reducing their numbers ✔
b. fish feed on zooplankton «therefore» increasing bacterial population ✔
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 ✔