The bulk fixation of carbon through photosynthesis takes place in

Identify $Z$ in the given figure representing the carbon cycle.

The given food web contains some missing organisms $A, B, C$ and $D$. Identify these organisms and select the correct answer.

Secondary producers are

Which one of the following types of organisms occupy more than one trophic level in a pond ecosystem?

Select the correct option for the following processes:
$P$ - Formation of organic components from inorganic components
$Q$ - Formation of inorganic components from organic components
Select the correct option for $P$ and $Q$.