Oxygen is $not$ produced during photosynthesis by

Who proposed the theory of photosynthesis in guard cells?

Which of the following statements with regard to photosynthesis is/are correct?
$I$. In $C_{4}$-plants,the primary $CO_{2}$ acceptor is $PEP$.
$II$. In the photosynthetic process,$PS-II$ absorbs energy at or just below $680 \;nm$.
$III$. The pigment that is present in the Pigment System-$I$ is $P680$.

During photosynthesis,which of the following processes occurs?

Approximately $9/10$ $(85-90\%)$ of the total photosynthesis on Earth is carried out by:

Which one does not differ between a $C_3$ and a $C_4$ plant?
$I.$ Initial $CO_2$ acceptor.
$II.$ Extent of photorespiration.
$III.$ Enzyme catalyzing reaction that fixes $CO_2$.
$IV.$ Presence of Calvin cycle.
$V.$ Leaf anatomy.