$A$: Estuary constitutes one of the most productive ecosystems.
$R$: It represents a transition zone between two populations of a species.

At which trophic level are carnivorous plants included?

Identify the possible link $A$ in the following food chain.
Plant $\rightarrow$ Insect $\rightarrow$ Frog $\rightarrow$ $A$ $\rightarrow$ Eagle

Which of the following statements are correct?
$(a)$ Net primary productivity is available biomass for consumption to heterotrophs.
$(b)$ Secondary productivity is defined as the rate of formation of new organic matter by heterotrophs.
$(c)$ The annual net primary productivity of the ocean is greater than that of land.
$(d)$ Warm and moist environment favours decomposition.

Consider the following statements concerning food chains.
$A.$ Removal of $80\%$ tigers from an area resulted in greatly increased growth of vegetation.
$B.$ Removal of most of the carnivores resulted in an increased population of deers.
$C.$ The length of food chains is generally limited to $3-4$ trophic levels due to energy loss.
$D.$ The length of food chains may vary from $2$ to $8$ trophic levels.
Which two of the above statements are correct?

Maximum biomass and variable organisms are found in