Botany MCQs for NEET — Practice Questions with Answers

The bud dormancy is induced by abscisic acid (ABA). The level of endogenous ABA increases with the onset of dormant period and decreases when it is broken.

Answer is (d)

Growth regulators are organic substances, other than nutrients, which in low concentration regulate growth, differentiation and development by promoting or inhibiting the same. Phytohormones are growth regulators produced naturally in plants and translocated to another region for regulating one or more physiological reactions when present in low concentration. Phytohormone can have at promoting or inhibiting effect on a process.

(d) Abscisic acid acts as a general plant growth inhibitor and an inhibitor of plant metabolism.
ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone.

(b) Auxins promote root initiation at a concentration which otherwise is inhibitory for growth of intact root. Auxins are often employed for inducing flowering in litchi and pineapple. Application of auxins to unpollinated pistils make them develop into seedless fruits or parthenocarps.

(c) Vernalisation refers specially to the promotion of flowering by exposure to a period of low temperature. Many temperate plants have vernalisation requirement and must experience a period of low temperature in winter, to initiate or accelerate flowering process, or in many fruit tree species, to induce dormancy and then break dormancy prior to flowering.

(b) Gibberellins induce the production of hydrolysing enzymes in the endosperm of germinating seeds. It stimulates the production of digestive enzymes like proteases, amylase and lipase which help to mobilise stored nutrients.

(c) Spraying juvenile conifers with gibberellins hastens their maturity period, thus leading to early seed production. Auxin controls xylem differentiation. Abscisic acid (ABA) increases the tolerance of plants to various kinds of stresses therefore, is also known as stress hormone.

(c) Gibberellic acid is also known as weak acidic plant growth regulator. It increases the yield of sugar by increasing the length of stem in sugarcane.
It is the only plant growth hormone that elongates the internodes to increase the height of the plant by causing an increase in the length of axis.

Lateral bud inhibition (apical dominance) is caused by the auxin diffusing basipetally from the apical bud. The lateral buds are more sensitive to higher concentration of auxins. It is known as theory of direct inhibition of auxin.