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

State one example of biological control of an invasive species.

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

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

Define biomagnification.

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;

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.

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

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

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.

In (c) Most candidates could define biomagnification.