Question
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The plants growing in dark show yellowing of leaves and elongated internodes, this condition is called as
(a) Etiolation
(b) Chlorosis
(c) Necrosis
(d) Wilting

Answer
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Hint: Etiolation is a process in which stems of the plants grown in dark elongate much more rapidly than normal causing the plant to grow whiten or grow pale.

Complete answer:Etiolation in plants is a phenomenon that occurs naturally and it is simply a plant’s way of reaching for a light source due to getting an inadequate amount.

If seeds are allowed to sprout without providing them with sufficient lighting, then it is observed that the seedlings grow rather spindly with a long and abnormal thin, pale stem. This is a prominent example of etiolation in plants. It is commonly known as plant legginess. Etiolation is the result of a type of hormones called auxins.

Auxins are actively transported from the growing tip of the plant downwards, resulting in the suppression of lateral buds. They generally stimulate the proton pumps in the cell wall which, in turn further increases the acidity of the wall and triggers expansion, an enzyme that weakens the cell wall. Although etiolation increases the probability that a plant will reach a light source, it gives rise to less than desirable symptoms.

Etiolation causes problems in plants such as abnormal lengthening of both stems and leaves, weakens the cell walls, elongates the internodes with fewer leaves than normal condition, and also may pave the path for chlorosis.

So, the correct answer is ‘Etiolation’.

Note:Etiolation happens because the plant is desperately searching for a light source, so in order to stop etiolation, the plant should be subjected to adequate light. All plants need sunlight to grow, although the amount of light required for normal growth varies from plant to plant.