Biotic factors involve the other organisms in the environment of an animal species. List two biotic factors that could affect the distribution of an animal species.

1.        ..................................................................

2.        ..................................................................

Research into a river ecosystem produced these approximate values: 25, 300, 6000 and 36 000 kJ m^–2 yr^–1. Using this data, construct a pyramid of energy showing four named trophic levels, each with their corresponding energy value.

predation;
competition;
disease;
food supply;

bars of decreasing size going upwards at least a third of the bar below;  
the trophic level on each bar labelled correctly;
 

Almost all correct answers, mainly food supply and competition.

For (b) candidates were able to draw and label the energy pyramid. In some cases the bars were not at least one third of the size of the previous bar, therefore scoring no mark for the drawing.