All food substances essential for life are obtained through ...... .

In which of the following is light energy stored in the form of chemical energy?

The most vital process for the existence of life on earth is

If $CO_2$ is released during respiration,why does the concentration of $CO_2$ in the atmosphere remain relatively constant?

Match the following pairs:
$(A)$ Emerson effect $(a)$ $C_4$ cycle
$(B)$ Hill reaction $(b)$ Photolysis
$(C)$ Calvin cycle $(c)$ $C_3$ cycle
$(D)$ Hatch and Slack cycle $(d)$ Photosystem-$I$ and $II$

Match the following columns:

Column-$I$	Column-$II$
$(A)$ $P_{680}$	$(I)$ Reaction centre of $PS-I$
$(B)$ $P_{700}$	$(II)$ Reaction centre of $PS-II$
$(C)$ $\text{LHC}$	$(III)$ Antennae
$(D)$ Plastoquinone	$(IV)$ Mobile carrier