(i) Hormone is an organic substance (e.g. a peptide or a steroid) that is secreted by one tissue. It limits the blood stream and induces a physiological response (e.g. growth and metabolism) in other tissues. It is an intercellular signalling molecule.
(ii) e.g. Testosterone, Thyroxine, Estrogen, Insulin, Oxytocin etc.

Vitamins are classified into two groups based on their solubility in water or in fat.
(a) Fat soluble vitamins:
These vitamins absorbed best when taken with fatty food and are stored in fatty tissues and livers. These vitamins do not dissolve in water. Hence they are called fat soluble vitamins. Vitamin A, D, E & K are fatsoluble vitamins.
(b) Water soluble vitamins:
Vitamins B (B₁, B₂, B₃, B₅, B₆, B₇, B₉ & B12) and C are readily soluble in water. On the contrary to fat soluble vitamins, these can't be stored. The excess vitamins present will be excreted through urine and are not stored in our body. Hence, these two vitamins should be supplied regularly to our body.

(i) Almost all carbohydrates are optically active as they contain one or more chiral carbons.
(ii) The number of optical isomers depends upon the number of chiral carbons (ie) 2ⁿ isomers, where n = total number of chiral carbons.
(iii) Glucose has \(4{ }^{\star} \)C; ∴ It has 2⁴ =16 isomers.

(i) Each protein has a unique three-dimensional structure formed by interactions such as disulphide bond, hydrogen bond, hydrophobic and electrostatic interactions. These interactions cain be disturbed when the protein is exposed to a higher temperature, certain chemicals such as urea, alteration of pH, ionic strength etc., It leads to the loss of the three-dimensional structure partially or completely. The process of a losing its higher order structure without losing the primary structure, is called denaturation. When a protein denatures, its biological function is also lost.
(ii) Since the primary structure is intact, this process can be reversed in certain proteins. This can happen spontaneously upon restoring the original conditions or with the help of special enzymes called cheperons (proteins that help proteins to fold correctly).
(iii) Example: coagulation of egg white by action of heat.