Question

Knots are formed in the wood due to
(a) External injuries
(b) Bases of the branches get buried in the main stem
(c) Leaf scars
(d) Insect bites

Answer 1

Hint: Wood is the cellular part of a plant and it consists mainly of xylem and pith inner to the cambium. Wood knots are generally formed by the shed of branches due to injury and also due to deviation of wood grains which make the surface dark in colour.

Complete answer:
Wood consists of all tissue present inside the cambium and it is considered as the cellular part of a plant. It consists of cellulose, lignin and hemicellulose. The strength of wood depends on fibres and fibres tracheids. In case due to injury or senescence when branches of tree fall off it leaves a scar on wood which is also known as bases. When these bases get covered by secondary tissues it leaves a dark spot which is also known as a wood knot. A wood knot is also formed by the deviation of grain to reach the inside part of the wood. A knot is circular or conical in shape and dark in colour and with the deposition of secondary tissue, it becomes hard. Minor wood knots do affect the wood but major wood knots make the wood weak without affecting in stiffness which leads to break down or crack of wood from the place of knots because when knots shed off it leaves a hole.

So, the correct answer is ‘Bases of the branches get buried in the main stem’.

Note:
Knot also forms due to infections like infection known as black knot disease, which forms a very harmful rampant knot in trees. A knot is of two types: the live knot is light in colour which does not fall off whereas dead knot dark in colour and shed off with time.