Amount of inorganic substances present in an ecosystem is . . . . . . Energy flow is a . . . . . . feature of ecosystem.

What is true about the phosphorus cycle?
$I.$ Rocks are the natural reservoirs of phosphorus.
$II.$ Weathering of sedimentary rocks makes phosphate available to the soil.
$III.$ Herbivores and carnivores obtain phosphorus from plants directly or indirectly.
Choose the correct option.

Mr. $X$ is eating curd/yoghurt. For this food intake in a food chain,he should be considered as occupying:

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

Match the following columns:

Column-$I$	Column-$II$
$(i)$ Ecosystem	$(P)$ Bacteria,Fungi
$(ii)$ Food chain	$(Q)$ Nutrient cycling
$(iii)$ Birds	$(R)$ Primary consumer
$(iv)$ Decomposers	$(S)$ Deer

Which of the following statements are correct regarding a food chain?
$(a)$ If $80\%$ of tigers are removed from an area,the growth of vegetation in that area increases.
$(b)$ If carnivores are removed from an area,the population growth of deer increases.
$(c)$ The length of a food chain is limited to $3$ to $4$ trophic levels because the amount of energy decreases in the ecosystem.
$(d)$ The length of a food chain is usually $2$ to $8$ trophic levels.