$99 \%$ of living systems are made up of four elements:

Which of the following is the correct match?

In organic compounds,the primary chemical bonds are formed between which atoms?

The variations observed among different species of organisms are due to the differences in their ......... .

Vitamin $A$ was discovered by

Select an appropriate chemical bond among ester bond,glycosidic bond,peptide bond and hydrogen bond and write against each of the following:
$(a)$ Polysaccharide
$(b)$ Protein
$(c)$ Fat
$(d)$ Water