According to one estimate,how many $kg$ of carbon is fixed in the biosphere through photosynthesis annually?

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

Photosynthesis is:
$I.$ Endergonic process
$II.$ Exergonic process
$III.$ Chemical process
$IV.$ Physical process
Select the correct option.

Choose the correct pair:

Who proposed the theory of photosynthesis in guard cells?

Assertion $:-$ There is not a complete one-to-one overlap between the absorption spectrum of chlorophyll $a$ and the action spectrum of photosynthesis.
Reason $:$ Most of the photosynthesis takes place in the blue and red regions of the spectrum,but some photosynthesis does take place at the other wavelengths of the visible spectrum.