NEET Practice Questions (MCQs) with Answers & Solutions

(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.

Refrigerated fruits maintain flavour and taste for longer period due to the slower rate of respirations. In low temperature. the respiration rate of fruits is minimised.

The biological clock measures the length of each night by the relative amount at red absorbing and far-red absorbing phytochrome present at dawn.

Abscisic Acid (ABA) is also called stress hormone. It is mildly acidic growth hormone which functions
as a general growth inhibitor by counteracting other hormones (auxin, gibberellin, cytokinin) or reactions mediated by them. It causes stomatal closure, abscission of flower and fruits while gibberellin helps in opening of stomata and promote development of fruits.

Photoperiodism is the response of plants to the relative length of day and night. Phototaxis is axis (movement) in which the stimulus is light. Phototropism is tropism in which stimulus is light, i.e., bending of plant towards light.

Abscisic acid (ABA) is a growth inhibitor, which is involved in seed dormancy. Dormant seeds germinate when ABA is overcome by gibberelllns. ABA cause dormancy in axillary buds and acts as stress hormone in adverse environmental conditions.

The commonly recognised class of plant hormones are auxin, gibberellin, cytokinin, ABA and ethylene. Some scientist believes that flower initiation is controlled by plant hormones callen florigen. A German plant physiologist George Melchers has also proposed the existance of vernalin (i.e., vernalisation initiating substance). Both these hormones are not been isolated so far. So, it still remains to be a hypothetical chemical.