In which of the following cycles is an atmospheric cycle absent?

$A$ simplified model of phosphorus cycling in a terrestrial ecosystem is given below. Identify $A, B, C$ and $D$.

$A$ farmer harvests his crop and expresses his harvest in three different ways.
$(a)$ $I$ have harvested $10$ quintals of wheat.
$(b)$ $I$ have harvested $10$ quintals of wheat today in one acre of land.
$(c)$ $I$ have harvested $10$ quintals of wheat in one acre of land,$6$ months after sowing.
Do the above statements mean one and the same thing? If your answer is yes,give reasons. If your answer is 'no',explain the meaning of each expression.

$A$ plant that is eaten by a herbivore,which is subsequently eaten by a carnivore,forms a/an ........

Who defined ecology as the study of structure and function of nature?

Climax communities: