In the carbon cycle,the source of carbon for plants is:

Select the correct option from the following.

If a lake is polluted by $DDT$,its highest concentration will be found in:

Assertion : In tropical rain forests,$O-$ horizon and $A-$ horizon of soil profile are shallow and nutrient-poor.
Reason : Excessive growth of micro-organisms in the soil depletes its organic content.

Distinguish between:
$(a)$ Grazing food chain and detritus food chain
$(b)$ Production and decomposition

The functional aspects of an ecosystem mainly include which of the following?