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.

Assertion $(A):$ $A$ natural ecosystem is usually self-sustainable.
Reason $(R):$ An ecosystem having producers,decomposers,and a source of energy is self-sustainable. Select the correct answer from the options given below:

Read the following statements carefully and answer the question given below:
$(1)$ $NPP = GPP - R$
$(2)$ Productivity of an ecosystem can be measured in $g/m^2/yr$ or $kcal/m^2/day$.
$(3)$ The total amount of energy produced by all producers in an ecosystem is called Gross Primary Productivity $(GPP)$.
$(4)$ The net primary productivity of the oceans is $55$ billion tons.
State the number of correct statements.

What type of food chain is the following?
Grass $\rightarrow$ Goat $\rightarrow$ Human

In a food chain,humans cannot be placed in which of the following trophic levels?

Which of the following can be identified as secondary consumers?