(a)  Explain briefly the following terms:

1. ecosystem;
2. abiotic environment.                                                         

(b)  List three ecological factors each which are specific to:

1. aquatic habitats;
2. terrestrial habitats.                                                           

(c)  State briefly the relationship between green grass and a rabbit in a given habitat.
(d)  Draw a typical pyramid of energy using four feeding levels.