$A$ food chain consists of:

Match the following Column-$I$ with Column-$II$:

Column-$I$	Column-$II$
$(i)$ Sedimentary cycle	$(P)$ Primary consumer
$(ii)$ Gaseous cycle	$(Q)$ Carbon
$(iii)$ Herbivore	$(R)$ Tertiary consumer
$(iv)$ Top carnivore	$(S)$ Sulphur

Fill in the blanks.
$(a)$ Plants are called as . . . . . . because they fix carbon dioxide.
$(b)$ In an ecosystem dominated by trees,the pyramid (of numbers) is . . . . . . type.
$(c)$ In aquatic ecosystems,the limiting factor for the productivity is . . . . . . .
$(d)$ Common detritivores in our ecosystem are . . . . . . .
$(e)$ The major reservoir of carbon on earth is . . . . . . .

Which of the following has the largest population in a food chain?

$A$: In hydrosere,the reed swamp stage is followed by the floating plant stage.
$R$: The sedge meadow stage has amphibious herbaceous plants.

In a food web,hyenas and vultures are: