Which of the following is a functional aspect of an ecosystem?

$A$ plant being eaten by a herbivore,which in turn is eaten by a carnivore,constitutes a:

Sun is the only source of energy for all ecosystems on the earth $EXCEPT$ for . . . . . . .

Energy contents of macrophytes may be estimated by

Which of the following is referred to as a food chain?

$A$ 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.