Assertion $A$: Aquatic organisms do not experience mechanical shocks while swimming in water.
Reason $R$: Water is a liquid medium for swimming.
Which option is correct for Assertion $A$ and Reason $R$?

How many of the following pairs are correct regarding the thermal tolerance of organisms?
$(1)$ Aves - eurythermal
$(2)$ Mammals - stenothermal
$(3)$ Amphibia - stenothermal
$(4)$ Reptile - eurythermal

Organisms occupying similar ecological niche but different geographical areas of distribution are called as

$A$ regulators are able to maintain homeostasis by means which ensure constant body temperature,constant osmotic concentration,etc. All $B$ and $C$ and a very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation).
Evolutionary biologists believe that the 'success' of mammals is largely due to their ability to maintain a constant body $D$ and thrive whether they live in Antarctica or in the Sahara desert.
Choose the correct option for $A, B, C$ and $D$.

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

Differentiate between Ectotherms and Endotherms.