Biology

Plant Growth and Hormones

695 Questions

Plant growth and hormones is a vital topic in biology that covers the physiological effects of different plant regulators like auxins, gibberellins, and cytokinins. These concepts are frequently tested in various general science sections of competitive exams. Practicing these questions helps clarify complex mechanisms like vernalisation, senescence, and tropism for test takers.

Abscisic acid effectsCytokinin functionsAuxins and tropismPlant tissue cultureSenescence in plantsNatural plant hormones

Plant Growth and Hormones Questions

Multiple choice

Which of the following hormone is responsible for causing seed dormancy?

  1. Indole acetic acid

  2. Gibberellic acid

  3. Abscisic acid

  4. Cytokinin
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Abscisic acid (ABA) is the plant hormone responsible for inducing and maintaining seed dormancy. It inhibits growth and helps seeds survive unfavorable conditions. IAA (auxin) promotes growth, gibberellic acid breaks dormancy, and cytokinins promote cell division.

Multiple choice

The role of auxin and cytokinin in the root and shoot formation was first given by:

  1. Robbins and Kotte

  2. Skoog and Miller

  3. Muir and others

  4. Steward and others
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Skoog and Miller (1957) discovered the critical balance between auxin and cytokinin in plant tissue culture. High cytokinin with low auxin promotes shoot formation, while high auxin with low cytokinin promotes root formation. This was a fundamental discovery in plant developmental biology.

Multiple choice

Leaf fall will occur when the contents of:

  1. auxins are increased

  2. auxins are decreased

  3. gibberellins are decrease

  4. gibberellins are increase
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Leaf abscission occurs when auxin production decreases, which happens naturally as leaves age or under stress conditions. The drop in auxin triggers the formation of the abscission layer at the leaf base, weakening the connection and causing leaf fall.

Multiple choice

Natural auxin is:

  1. NAA

  2. IAA

  3. 2,4-D

  4. Aviton

  5. Both (a) and (b)
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

IAA (Indole-3-acetic acid) is the primary natural auxin produced by plants. NAA (naphthaleneacetic acid) and 2,4-D are synthetic auxins used in agriculture. Aviton appears to be an incorrect or obscure term.

Multiple choice

Which of the following sentences are in accordance with direct inhibition hypothesis?

  1. Auxins from axillary buds travel up to apical buds to stimulate bud growth.

  2. Cytokinins move from roots to shoot signalling lateral bud growth.

  3. Cytokinins move from shoot to root to induce root morphogenesis.

  4. Auxin from apical buds travel down shoots to stimulate auxiliary bud growth.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This is true. Cytokinin moves from the roots into the shoots, eventually signalling lateral bud growth.