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

In 1925, the Japanese biologist Kurosawa showed that the bakanae (foolish seedling) disease of rice was caused by a substance produced by the fungus Gibberella fujikuroi. The substance was named gibberellin and was shown to cause elongation of stem tissues. Which of the following statements about gibberellins is false?

  1. The gibberellins produced by the fungus caused normal healthy rice plants to become unusually tall.

  2. Dwarf pea plants have a mutation in the gibberellin biosynthesis pathway.

  3. If gibberellin is applied to the stems of dwarf pea plants, the stems elongated so that the plant reach normal health.

  4. Pea plants carrying the dwarf mutation would be expected to have higher levels of gibberellin in their stems than normal plants.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The question asks for the FALSE statement. Dwarf pea plants have mutations that REDUCE gibberellin production or sensitivity, which is why they're dwarf. Therefore, they would have LOWER levels of active gibberellin, not higher. Option D correctly identifies this as false by stating they would have 'higher levels' - this is the lie. Options A, B, and C are all true statements about gibberellins.

Multiple choice

Why does a plant appear to bend towards light?

  1. Due to the diffusion of auxins towards the shady side of the shoot

  2. Due to the diffusion of gibberellins towards the bright side of the shoot

  3. Due to the diffusion of cytokinins towards the shady region of the shoot

  4. Due to the diffusion of gibberellins towards the shady region of the shoot
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When light is incident on one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot, which is away from light. Thus, the plant appears to bend towards light.

Multiple choice

Choose the correct match.

 
GROUP I GROUP II
(i) Auxine A. Prevent aging
(ii) Cytokinine B. Change sex of unisexual plant
(iii) Ethylene C. Root regeneration
(iv) ABA D. Stimulate lateral growth

  1. i - B, ii - A, iii - D, iv - C

  2. i - C, ii - A, iii - D, iv - B

  3. i - A, ii - C, iii - D, iv - B

  4. i - C, ii - A, iii - B, iv - D
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Auxine helps to promote the meristemic tissue, i.e. root. Cytokinine prevents senescence or aging. Ethylene stimulates lateral growth of plant tissue. ABA or abscisic acid is used for changing sex of unisexual plant; it has an economical value.

Multiple choice

Abscisic acid causes _____________.

  1. faster leaf fall

  2. dormancy of tubers

  3. retardation of growth

  4. senescence of leaves

  5. all of the above are correct
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

All the options are correct and reveal the functions of ABA.

Multiple choice

Apical dominance in higher plants is due to _____________.

  1. balance between auxin and cytokinin

  2. enzymatic activity

  3. carbohydrate and nitrogen ratio

  4. photoperiodism

  5. the presence of apical dominance
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

It is true that auxin and cytokinin ratio controls morphogenesis in higher plants and thus regulating the apical dominance.

Multiple choice

Which is the role not played by ethylene?

  1. Inhibition of elongation of stem.

  2. It increases the number of female flowers and reduces the number of male flowers.

  3. It causes ripening of fruits.

  4. It causes abscission of leaves.

  5. It increases maleness in some plants.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

This function is promoted by gibberellin.

Multiple choice

Which is not the specific function of auxin?

  1. Helps in apical dominance.

  2. Induces parthenocarpy

  3. Control of weeds

  4. Prevention of lodging

  5. Fruit ripening
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

It is the exclusive feature of ethylene and not auxins.

Multiple choice

Which hormone is antagonistic to activity of auxins?

  1. Cytokinin

  2. Gibberellin

  3. Calcitonin

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

Abscisic acid is a growth inhibitor and acts as an opponent to the activity of auxins. Auxins have a cardinal role in the coordination of many growth and behavioural processes in the plant's life cycle and are essential for the development of plant body. 

Multiple choice

Find the mismatched pair:

  1. Cytokinin : promotes cell division

  2. Auxin : cell enlargement

  3. Ethylene : phototropism in shoot

  4. Abscisic acid : wilting of leaves
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Ethylene is a fruit ripening hormone.