Abiotic and biotic factors combine to create a system called (ecosystem/hydrosphere).

In natural ecosystems, decomposers are

Choose the appropriate word and fill in the blank:

A _____ (producer/consumer) makes its own food energy and begin the food chain.

The _____ is the main source of energy in self-sustaining ecosystem.

Various levels or steps in a food chain in which transfer of food takes place from one organism to another are called _____ levels.  

Fill in the blank with suitable word:

The amount of biomass/organic matter produced by producer per unit area over a period of time is called _____ (primary productivity/secondary productivity).