How many sentences are correct?
$(1)$ The trophic levels in $GFC$ are unlimited.
$(2)$ Organisms at each trophic level depend on those at the higher trophic level for their energy demands.
$(3)$ Plants capture only $2-10$ percent of $PAR$.
$(4)$ All organisms are dependent for their food on producers, either directly or indirectly.

Succession in a $6 \ m$ deep pond exhibits a sequence of

If carbon dioxide is withdrawn from the biosphere,which organism would first experience negative effects?

The bulk fixation of carbon through photosynthesis takes place in

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 are known as the 'pioneer species' in primary succession?