Differentiate between biodegradable and non-biodegradable substances. Cite examples.

Pesticides added to the field is seen in increased amounts in the crop and in the birds that feed on them. What is the phenomenon called?

Why is a lake considered to be a natural ecosystem?

Why do all food chains start with plants and have a limited number of tropic levels?

What is ozone? Name the chemicals that damage the ozone layer.