Invertebrates living in the deep sea, at extreme depths, experience pressure how many times greater than the normal atmospheric pressure (in $\times$)?

Define/Explain: Ecological niche.

$A$ physical place or set of environmental conditions around the organism to which it must adapt to survive and prosper is . . . . . . .

Do you agree that regional and local variations exist within each biome? Substantiate your answer with suitable examples.

In a sea shore,the benthic animals live in sandy,muddy and rocky substrata and accordingly developed the following adaptations:
$(a)$ Burrowing
$(b)$ Building tubes
$(c)$ Holdfasts / peduncle
Match the suitable substratum against each adaptation.

Despite variations in external environment,organisms try to maintain constancy of its internal environment which is called . . . . . . .