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

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

Consider the following statements :

  1. In climacteric fruits, ethylene stimulates its own production.
  2. Gibberellin present in a healthy stem cuases some of the new cells to differentiate as phloem.
  3. Loss of turgor in leaves stimulates the productions of abscisic acid Which of the statements given above are correct ?

  1. 1 and 2 only

  2. 2 and 3 only

  3. 1 and 3 only

  4. 1,2 and 3
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Climacteric fruits show autocatalytic ethylene production where ethylene stimulates its own biosynthesis. Gibberellins can cause phloem differentiation in stem tissue. Abscisic acid (ABA) production is triggered by water stress and loss of turgor pressure in guard cells. All three statements are physiologically accurate.

Multiple choice

Which one of the following statements is not correct ?

  1. Roots produce gibberellins

  2. The Casparian strips in roots are involved in controlling the types of minerals that enter the xylem water stream

  3. Lateral roots are initiated by cell division in the endodermis

  4. When Rhizobium converts N2 into nitrogenous compounds that are released into the host cells, energy is supplied by sugars from the legume root cells
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The question asks which statement is NOT correct. Lateral roots originate from the pericycle (a layer of cells inside the endodermis), not from the endodermis itself. The other statements are all accurate: roots do produce gibberellins, Casparian strips regulate mineral entry into the xylem, and Rhizobium's nitrogen fixation is powered by host-derived sugars.

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

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

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.

Multiple choice

Scientifically, plant hormone is an organic compound produced in one part of plant and transmitted to other parts in very low concentration casuing physiological responses. 5 major types of endogenous plant growth substances or plant hormones are- auxin, gibberellins, cytokinins, abscis acids and ethylene.

Which of the following types of plant hormones is the alternative for low temperature treatment?

  1. Cytokinin

  2. Ethylene

  3. Auxin

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

Gibberellin is the alternative plant hormone for low temperature treatment. In variety of plants seed germination is controlled differently by abscisc acid and gibberellins. 

Multiple choice

Scientifically, plant hormone is an organic compound produced in one part of plant and transmitted to other parts in very low concentration casuing physiological responses. 5 major types of endogenous plant growth substances or plant hormones are- auxin, gibberellins, cytokinins, abscis acids and ethylene.

Polar transport of auxin in the segments of stem includes the movement of auxin from ___________.

  1. base towards the lateral branches

  2. base towards the morphological apex

  3. morphological apex towards the base

  4. morphological apes towards the lateral braches
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Polar transport of auxin in the segments of stem includes the movement of auxin from morphological apex towards the base.

Multiple choice

The chemical defoliant ‘Agent Orange’ was banned because

  1. the synthetic auxin used in the preparation, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), caused premature growth in humans

  2. the synthetic auxin used in the preparation, 2, 4, 5-trichlorophenoxyacetic acid (2,4,5-T), caused plants to grow more vigorously than the environment could sustain

  3. a contaminant in the preparation of 2, 4, 5-trichlorophenoxyacetic acid (2,4,5-T) caused disease and birth defects in humans

  4. a contaminant in the preparation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) killed beneficial plants
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Agent Orange—or Herbicide Orange (HO)—is one of the herbicides and defoliants used by the U.S. military as part of its herbicidal warfare program, Operation Ranch Hand, during the Vietnam War from 1961 to 1971. It was a mixture of equal parts of two herbicides, 2,4,5-T and 2,4-D. According to a study by one Vietnamese scientist, Dr. Nguyen Viet Nhan, children in the areas where Agent Orange was used have been affected and have multiple health problems, including cleft palate, mental disabilities, hernias, and extra fingers and toes. Hence, it was banned.