a) Primary producers (PP): They are autotrophic organisms that fix up the solar energy and manufacture their own food from inorganic raw material. So, they form the base of the food chain constituting the first trophic level (T1). E.g. Grass
b) Primary consumers (PC) or Herbivores: There are animals that feed on green plants or plant products, so they constitute a second trophic level (T2). E.g. Rabbit
c) Secondary consumers (SC) or Primary carnivores: These are animals that feed on herbivores and form third level (T3). E.g. Crow
d) Tertiary consumers (TC) or Secondary carnivores: These are animal that feeds on secondary consumers constitute the fourth trophic level (T4). E.g. Vulture