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

Gibberellins were extracted from _______.

  1. bacteria

  2. algae

  3. virus

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

Gibberellins were first isolated from the fungus Gibberella fujikuroi, which causes foolish rice disease (excessive elongation). They are plant hormones that promote growth.

Multiple choice

Plant growth hormones extracted from a fungus and a fish are respectively

  1. auxins and 2, 4-D

  2. ethylene and cytokinin

  3. gibberellin and kinetin

  4. gibberellin and zeatin
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Gibberellins were first discovered from the fungus Gibberella fujikuroi causing foolish seedling disease in rice. Kinetin (a cytokinin) was isolated from herring sperm DNA. Auxins occur naturally in plants, and 2,4-D is synthetic. Ethylene is a gaseous hormone produced by plants.

Multiple choice

The important finding in Went's experiment was

  1. that the curvature of coleptile was proportional to the concentration of auxins

  2. the presence of elongation promoting substance in all cells of root

  3. that the curvature in few coleoptiles was due to irregular elongation of cells

  4. that there is unequal distribution of elongation promoting substance in Avena coleoptile
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

F.W. Went's classic Avena coleoptile experiment (1928) demonstrated that the curvature response was directly proportional to the concentration of auxin. By placing agar blocks containing different auxin concentrations on decapitated coleoptiles, he showed that higher concentrations produced greater curvature - establishing the quantitative relationship between auxin and tropic response.

Multiple choice

The phenomenon of apical dominance is exhibited by

  1. Gibberellins

  2. Auxin

  3. Cytokinins

  4. Abscisic acid
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Apical dominance is exhibited by auxins as their presence in the tip stimulates the growth of apical bud, but suppresses the growth of lateral buds.

Multiple choice

Which of the following sentences about auxins is incorrect?

  1. Auxins promote root initiation.

  2. Auxins induce the formation and organisation of phloem and xylem.

  3. Auxins are required for fruit growth and development, and they delay fruit senescence.

  4. Auxins promotes abscission and cause early formation of abscission layer.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Auxins inhibit abscission prior to formation of abscission layer. Thus, they inhibit senescence of leaves.

Multiple choice

Choose the incorrect match.

  1. Morphogenesis - Cytokinins and auxins

  2. Richmond Lang effect - Cytokinin

  3. Breaking seed dormancy - Abscisic acid

  4. Apical dominance - Auxins
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Abscisic acid causes dormancy of seeds.

Multiple choice

Cytokinins work in association with

  1. gibberellins

  2. auxins

  3. ethylene

  4. florigen
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Cytokinins never work alone. In the presence of auxins, they stimulate cell division.