How many molecules of water are needed by a green plant to produce one molecule of hexose or to reduce $6$ molecules of $CO_2$?

Read the following four statements ($a, b, c,$ and $d$) carefully and select the option that includes both correct statements.
$(A)$ The $Z$-scheme of light reaction occurs only in the presence of $PSI$.
$(B)$ Only $PSI$ is functional in cyclic photophosphorylation.
$(C)$ Cyclic photophosphorylation results in the synthesis of $ATP$ and $NADPH_2$.
$(D)$ Stroma lamellae lack both $PS-II$ and $NADP$ reductase $(FNR)$.

Which would do maximum harm to a tree?

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

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

Name the two important enzymes of $C_3$ and $C_4$ pathways, respectively. What important role do they play in fixing $CO_2$?