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 statements is/are false?

a. In nasties, the direction of movement is not determined by the direction of stimulus. b. Gibberellins promote the wiltering and falling of leaves. c. The roots of a plant are negatively phototrophic.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This is the correct option as this statement is false. Abscisic acid promotes the wiltering and falling of leaves.

Multiple choice

Which of the following is incorrect about ethylene?

  1. It promotes elongation of stems and root, especially in dicot.

  2. Its biosynthesis involves the enzyme ACC synthase.

  3. It promotes flowering in Bromeliads (the pineapple family).

  4. It enhances lateral or radial expansion of cell.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Ethylene promotes stem and root elongation in MONOCOTS (like rice), but in DICOTS, it actually inhibits elongation and promotes swelling. This makes statement A incorrect. B is true - ACC synthase is key in ethylene biosynthesis. C is true - ethylene induces flowering in Bromeliads including pineapple. D is true - ethylene promotes radial/lateral expansion (the 'triple response' in seedlings). Therefore A is the incorrect statement.

Multiple choice

Which of the following is not a part of the triple response of etiolated pea seedling to ethylene?

  1. Stunted growth

  2. Increased radial expansion of cells of the stem

  3. Loss of gravity perception

  4. Unfolding of the apical hook of the seedling
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The triple response to ethylene in etiolated seedlings consists of three components: inhibited elongation, increased radial expansion (swelling), and epinasty. Loss of gravity perception is not part of this response. The unfolding of the apical hook is actually one of the observed effects.

Multiple choice

An efficient root-inducing chemical useful in horticulture is

  1. GAA

  2. IBA

  3. NAA

  4. 2, 4 – D
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Indole Butyric Acid (IBA) is applied to cut end of the stem to stimulate rate of formation and increase the number of roots. It is useful in horticulture as promotion of rooting would reduce death rate in nursery plants.

Multiple choice

Which of the following is correct about a plant which has a good level of abscisic acid?

  1. Growth in stem will slow down.

  2. Growth in roots will speed up.

  3. Ageing in leaves will be delayed.

  4. Leaves will wilt and fall.

  5. The plant will grow rapidly because of shoot elongation.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Abscisic acid is a growth inhibitor and the process of wilting and falling of leaves is called abscission. It also causes the detachment of fruits and flowers from the plant.

Multiple choice

Which of the following statements is/are correct?

a. Plants do not have a nervous system. b. Plants use hormones for coordination. c. Plants respond to stimuli very slowly by growing.

  1. a, b and c

  2. a and b

  3. a and c

  4. b and c

  5. Only c
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Plants do not have a nervous system. They use only hormones for coordination. They respond to stimuli very slowly as they do not have a nervous system and their response is reflected by their growth.

Multiple choice

The parthenocarpy has been introduced in egg-plant by inserting a bacterial gene responsible for the synthesis of (1) gibberellins (2) cytokinin (3) auxin

  1. Only 1 and 2

  2. Only 1 and 3

  3. Only 2

  4. Only 3
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Bacterial genes for auxin biosynthesis (such as iaaM and iaaH from Pseudomonas syringae) can be inserted into plants to induce parthenocarpy - the development of fruit without fertilization. Auxin is the primary hormone responsible for fruit set and development. Gibberellins and cytokinins are not the primary hormones for this purpose.