Vitamins are organic compounds required in the diet in small amounts to perform specific biological functions for normal maintenance of optimum growth and health of the organism. Their deficiency causes specific diseases. Most of the vitamins cannot be synthesised in our body, but plants can synthesise almost all of them.
Vitamins are classified into two groups depending upon their solubility in water or fat. Vitamins which are soluble in fat and oils but insoluble in water are called fat soluble vitamins. These are vitamins A, D, E and K. They are stored in liver and adipose (fat storing) tissues. B group vitamins and vitamin C are soluble in water and are called water soluble vitamins. Water soluble vitamins must be supplied regularly in the diet because they are readily excreted in urine and cannot be stored (except vitamin B12) in our body.
The function of enzymes in living systems is to:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → catalyse biochemical reactions
Enzymes are biocatalysts, mostly globular proteins. They speed up the reactions of living cells so that these run under the mild conditions of the body, and each enzyme is specific for its reaction and substrate; for example, maltase catalyses the hydrolysis of maltose into glucose.
Why the other options are incorrect
Option (1) transport oxygen — Incorrect. Oxygen is carried by haemoglobin, the iron complex of blood, not by enzymes.
Option (2) provide immunity — Incorrect. Defence against infection is not an enzyme’s role; an enzyme only speeds up a particular reaction.
Option (4) provide energy — Incorrect. Energy comes from the oxidation of food such as glucose. An enzyme, being a catalyst, is not used up and supplies no energy itself.
NCERT (2026-27 edition):
10.3 Enzymes – “Life is possible due to the coordination of various chemical reactions in living organisms. … This process involves a sequence of reactions and all these reactions occur in the body under very mild conditions. This occurs with the help of certain biocatalysts called enzymes. Almost all the enzymes are globular proteins.”