The food chain is the sequence of population or organisms through which food and its contained energy pass in an ecosystem with members at one step becoming the food of later step of the sequence. In the grassland food chain, the green plant (grass) is the primary producer which makes the food. The rat is the primary consumer. The bird is the secondary consumer. The snake is the tertiary consumer which feeds on the bird. The pyramid for the flow of number is upright because the number of the organisms decreases with the increase in the trophic level.