$A$ quaternary protein consisting of two $\alpha$-chains and two $\beta$-chains is:

Haemoglobin molecule is made up of

In the given figure,what does $A$ indicate?

Which of the following amino acids is an essential part of the human diet?

The $pH$ value of a solution in which a polar amino acid does not migrate under the influence of an electric field is called:

Match the following columns correctly.

Column $I$	Column $II$
$(a)$ Actin	$(i)$ Transport of respiratory gases
$(b)$ Immunoglobulin	$(ii)$ Immunity
$(c)$ Melanin	$(iii)$ Pigmentation of the body
$(d)$ Hemoglobin	$(iv)$ Muscle movement