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Date May 2012 Marks available 1 Reference code 12M.3.SL.TZ2.21
Level Standard level Paper Paper 3 Time zone Time zone 2
Command term State Question number 21 Adapted from N/A

Question

Explain how living organisms can affect the abiotic environment during primary succession.

[3]
a.

State one example of biological control of an invasive species.

 

Invasive species:  ......................................................          

 

Biological control:  ......................................................           

[1]
b.

Define biomagnification.

[1]
c.

Markscheme

remains/debris/litter from growth/death of plants can increase soil depth;
remains/debris/litter from growth/death of plants can increase soil mineral content;
remains/debris/litter from growth/death of plants can alter soil pH;
remains/debris/litter from growth/death of plants can improve soil water retention and reduce drainage;
growth of (larger) plants can reduce erosion though binding action of roots;

a.

example of invasive species and an example of its biological control
e.g.:
prickly pear cactus is controlled by moth (Cactoblastis cactorum)
Accept other suitable example.

b.

a process when chemical substances become more concentrated at each trophic level

c.

Examiners report

Many candidates did not know how plants affected the environment in a primary succession. 

a.

Many incorrect answers. Some candidates invented examples of biological control. In some cases, the candidate mentioned an invasive species and then a different example of biological control.

b.

In (c) Most candidates could define biomagnification.   

c.

Syllabus sections

Option C: Ecology and conservation » Option C: Ecology and conservation (Core topics) » C.3 Impacts of humans on ecosystems
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