Based on the medium of habitat,how many types of ecosystems are there?

In the food chain
Grass $\rightarrow$ Deer $\rightarrow$ Lion
operating in a forest,what will happen if all the
$(a)$ lions are removed?
$(b)$ deers are removed?

Define a food web. State its significance for an ecosystem.

List two causes of depletion of the ozone layer. Mention any two harmful effects of the depletion of this layer.

Mention the differences between food habits of organisms belonging to the first and third trophic level. Give one example of each of them.

Accumulation of harmful chemicals in our body can be avoided. Explain how this can be achieved.