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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 Outline 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.

[1]
a.

Assuming that the populations of bacteria are under bottom-up control, identify the mesocosms in which the bacterial populations will be highest.

[1]
b.

Outline top-down effects on the bacteria in the four mesocosms. 

[2]
c.

Suggest advantages of undertaking this experiment in the sea rather than in the laboratory.

[2]
d.

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

a.

soil and no fish «mesocosm» AND soil and fish «mesocosm» ✔

Both mesocosms required

Accept answers such as “the two with soil”.

b.

a. zooplankton feed on bacteria reducing their numbers ✔

b. fish feed on zooplankton «therefore» increasing bacterial population ✔

c.

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 ✔

 

d.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.
[N/A]
d.

Syllabus sections

Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics) » C.2 Communities and ecosystems
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