What is the cause of the variations found in different species of living organisms?

Molecules are always moving. Some molecules move faster than others; . . . . . . is a measure of their average velocity of movement.

Heat is distributed uniformly throughout the body of a living organism because...

Match Column-$I$ with Column-$II$:

Column-$I$	Column-$II$
$(1)$ Cellulose	$(p)$ Acidic
$(2)$ Tyrosine	$(q)$ $CH_2-OH$ containing
$(3)$ Serine	$(r)$ Aromatic
	$(s)$ Homopolymer

Given below are two statements:
Statement $I$: $A$ protein is imagined as a line,the left end represented by the first amino acid ($N$-terminal) and the right end represented by the last amino acid ($C$-terminal).
Statement $II$: Adult human haemoglobin consists of $4$ subunits (two subunits of $\alpha$ type and two subunits of $\beta$ type).
In the light of the above statements,choose the correct answer from the options given below:

The common immediate source of energy in cellular activity or the energy currency of the cell is: