The biome characterized by a layer of permafrost is known as:

When an organism moves away temporarily from a stressful habitat to a more hospitable area and returns when the stressful period is over,what is this process called?

$I.$ Many xerophytic plants have thick cuticle on leaf epidermis and sunken stomata.
$II.$ Some xerophytic plants have a special photosynthetic pathway $(CAM)$ that enables their stomata to close during the day.
$III.$ $Opuntia$ has spines (modified leaves) and a photosynthetic phylloclade (stem).
$IV.$ All adaptations are genetically fixed in all organisms.
Choose the combination of correct statements.

Populations of different species living together in a common habitat form which of the following?

To which habitat is the elephant adapted?

Given below are two statements:
Statement $I$: Stenohaline animals tolerate a wide range of salt concentration.
Statement $II$: Euryhaline animals are capable of handling a narrow range of salt concentration.
In the light of the above statements,choose the most appropriate answer from the options given below: