The balance between $CO_2$ and $O_2$ in the atmosphere is maintained by:

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?

The mean photosynthetic rates of $C_3$ and $C_4$ plants per $dm^2$ per hour are respectively:

Plants in which the first product of $CO_{2}$ fixation is $C_{3}$ acid,i.e.,the ...$A$... pathway,and those in which the first product was $C_{4}$ acid $(OAA)$,i.e.,the ...$B$... pathway. Complete the given statement by filling appropriate options in the given blanks.

Assertion : Dark reaction occurs only at night in the stroma of chloroplast.
Reason : $CO_2$ fixation occurs only during $C_3$ cycle.