Biology

Plant Growth and Hormones

727 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

Match the following: Plant growth regulators|Examples| |a. Adenine derivative|1. Abscisic acid| |b. Derivative of carotenoids|2. Kinetin| |c. Terpenes|3. Gibberellic acid|

  1. a - 3, b - 1, c - 2

  2. a - 3, b - 2, c - 1

  3. a - 1, b - 2, c - 3

  4. a - 2, b - 1, c - 3

  5. a - 2, b - 3, c - 1
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

An example of adenine derivative is kinetin. An example of derivative of carotenoids is abscisic acid. An example of terpene is gibberellic acid.

Multiple choice

Which of the following is not a use of auxins?

  1. Auxins are widely used as herbicides.

  2. Auxins help prevent fruit and leaf drop at early stages.

  3. Auxins promote flowering.

  4. Auxins delay senescence.

  5. Auxins help in initiating rooting in stem cuttings.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This is the correct option as this is not a use of auxins. Gibberellins delay senescence.

Multiple choice

Which one of the following activates cambium and elicites differentiation of xylem ?

  1. Abscisic acid

  2. Auxin

  3. Cytokinin

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

Auxin (IAA) is the primary hormone that stimulates vascular cambium activity and promotes differentiation of cambial derivatives into xylem (secondary growth). Cytokinins promote cell division but not specifically xylem differentiation. ABA inhibits growth; ethylene regulates fruit ripening and senescence.

Multiple choice

Assertion (A) : If the oat seedling are exposed to unilateral illumination, the stem bends towards the light. Reason (R) : An auxin gradient is established in the coleoptile by the destruction of auxin in the lighted side and extra synthesis of auxin in the darker side.

  1. Both A and R are individually true and R is the correct explanation of A

  2. Both A and R are individually true but R is not the correct explanation of A

  3. A is true but R is false

  4. A is false but R is true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Phototropism (bending toward light) in oat coleoptiles is caused by an auxin gradient. Current understanding indicates that auxin redistribution occurs through lateral transport (PIN proteins) rather than differential destruction/synthesis. The dark side accumulates more auxin, causing elongation and bending toward light. While the reason mentions auxin gradients (which is correct), the mechanism described (destruction in light, extra synthesis in dark) is outdated. However, for the level of this question, it may be accepted as explaining the gradient.

Multiple choice

With which of the following is Richmond Lang effect associated?

  1. Stimulation of rosette plants to grow normal

  2. Inhibition of glycolysis by oxygen

  3. Inhibition of photosynthesis by oxygen

  4. Delay of senescence in leaves
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The delay of senescence of leaves and other organs of the plants by cytokinins is called Richmond Lang effect.

Multiple choice

Which of the following hormones causes delay in senescence?

  1. Indole butyric acid

  2. Gibberlic acid

  3. Cytokinin

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

Cytokinins are plant hormones that delay senescence (aging) by promoting cell division, protein synthesis, and nutrient mobilization. They keep leaves green and slow aging. Abscisic acid promotes senescence and dormancy, gibberellic acid promotes stem elongation, and indole butyric acid (IBA) is an auxin involved in rooting.

Multiple choice

Which of the following hormones promotes inter-nodal elongation?

  1. Auxin

  2. Gibberellic acid

  3. Cytokinin

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

Gibberellic acid (GA) promotes internodal elongation in plants, making stems longer between nodes. This is especially important in dwarf varieties and during bolting. Auxins promote cell elongation but are more associated with apical dominance and phototropism. Cytokinins promote cell division, and abscisic acid inhibits growth.

Multiple choice

Which of the following is a synthetic plant hormone?

  1. IAA

  2. 2, 4 - D

  3. GA

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

2,4-D (2,4-dichlorophenoxyacetic acid) is a synthetic auxin widely used as a herbicide and plant growth regulator. IAA is natural auxin, GA represents gibberellins, and Zeatin is a natural cytokinin produced in plants.

Multiple choice

On exposure to a shock or automated blow the leaflets of Mimosa pudica plant close upwards and its lower portion of petiole contracts. What is this movement called?

  1. Autonasty

  2. Seismonasty

  3. Epinasty

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

On exposure to a shock or automated blow the leaflets of Mimosa pudica plant close upwards and its lower portion of petiole contracts—this movement is called Seismonasty, which is the nastic response of plants or fungus to touch.  

Multiple choice

What happens at the time of senescence of the plant?

  1. Secondary plant products accrue in tissues and organs at the time of aging.

  2. Metabolite such as carbohydrates, proteins, etc., are transmitted out of aging leaves to young leaves.

  3. Metabolite such as carbohydrates, proteins, etc., are transmitted out of young leaves to aging leaves.

  4. The plant shows serial senescence of leaves.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

At the time of senescence of the plant the plant shows serial senescence of leaves. In such condition or process the plants degeneration takes place with the age. 

Multiple choice

When short day plant (SD) and long day plant (LD) both are preserved under friendly condition for flowering and are exposed to short flash of red light in mid of dark period then

  1. SD plant will flower and LD plant will remain productive.

  2. SD plant will remain productive and LD plant will flower.

  3. Both SD and LD plants will flower.

  4. Both SD and LD plants will remain productive.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

SD plant will remain productive and LD plant will flower. Short day plants produce flowers only when the length of day is less than 12 hours long day plants bloom when they get light more than 12 hours. 

Multiple choice

Recognize the following options regarding plants’ growth movements: (a) Growth movements in the flowering plants are always triggered by the external stimuli like light and gravity. (b) Varying growth of cells in various parts of affected organ causes growth movements. (c) Growth movements are extremely slow and may be observed only via time-lapse photography. Which of the above statements is/are true?

  1. b and c are true.

  2. a, b and c are true.

  3. a and c are true.

  4. a and b are true.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Growth movements are extremely slow and may be observed only via time-lapse photography. Varying growth of cells in various parts of affected organ causes growth movements.