ICSE Class 8 Answered

All living things depend on their environment to supply them with food, water, and shelter. Their environment consists of physical factors such as soil, air, and temperature and also of other organisms. Many living things interact with other organisms in their environment. In fact, they may need other organisms in order to survive. This is known as interdependence. For example, living things that cannot make their own food must eat other organisms for food. 

There are three types of interactions among organisms:
      (a)   Predator-prey
      (b)   Symbiosis that consists of commensalism, mutualism and parasitism.
      (c)   Competition