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 apical dominance auxins and gibberellins growth and development plant growth and development biology

Apical dominance in plants means

  1. Growth of lateral buds

  2. Inhibition of growth of lateral buds

  3. Both A and B

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Apical dominance is a phenomenon in which central stem is dominant and growth of lateral buds is inhibited. It is due to plant hormones produced in the tip of the shoot. Auxin hormone is responsible for apical dominance and cytokinin hormone is responsible for breaking the apical dominance. 

Thus, the correct answer is option B.

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

In a garden, the gardener cut the apical bud of Lawsonia (mehandi) because 

  1. The length should be limited in Lawsonia.

  2. Due to the cutting of apical bud, the effect of Auxins decreases and lateral bud grows and forms dense appearance that is why it can give a definite shape.

  3. Other apical bud grows quickly due to cut of apical bud.

  4. Due to the cutting of apical bud effect of Ethylene decreases and the plant grows rapidly.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Apical buds produce auxins, which inhibit the growth of lateral buds. By removing the apical bud, the auxin concentration drops, allowing lateral buds to grow, which creates a bushier, denser plant suitable for hedges like Lawsonia.

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

In the proms of apical dominance, lateral buds are unable to grow in the presence of apical bud. This is due to

  1. Less amount of auxin in apical bud

  2. More amount of auxin in apical bud

  3. Less amount of cytokinins in lateral buds

  4. More amount of cytokinins in lateral buds.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Apical dominance is the phenomenon by which presence of apical bud does not allow the nearby lateral buds to grow. When the apical bud is removed, the lateral buds sprout. Apical bud inhibits the growth of lateral buds by releasing auxins. When a plant is decapitated i.e., its apical bud is removed then the lateral buds sprout, resulting in dense bushy growth. This phenomenon is widely used in the tea plucking and hedge making.
So the correct answer is 'More amount of auxin in apical bud'.
Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Removal of auxin source demonstrates that leaf abscission is ........... by auxin, and apical dominance is ............ by auxin.

  1. promoted, promoted

  2. inhibited, inhibited

  3. promoted, inhibited

  4. inhibited, promoted
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Shedding of mature leaves from the stem or ripe fruits from the stem is called abscission. Generally, a layer of tissue is formed at the base of the organ. This layer of tissue is called abscission zone. Abscission zone does not occur when the concentration of auxin is high, particularly when the gradient of auxin is steep i.e., more auxin on the distal side and less auxin on the proximal side. The abscission zone formation occurs rapidly when the auxin gradient becomes slight or neutral. Moreover, the plant hormone ethylene is found to promote the abscission. Thus, a high concentration ocean prevents the formation of abscission layer and the phenomenon is controlled by the concentrations of auxin and ethylene. Apical dominance is promoted by auxin.
So the correct answer is "inhibited, promoted".
Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

The hormone responsible for apical dominance is

  1. IAA

  2. GA

  3. ABA

  4. Florigen
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Indole Acetic Acid IAA is a naturally produced hormone at the shoot tip by the apical bud that results in vertical growth of the stem, however, this inhibits the growth of lateral buds by preventing basipetal transportation of auxin. Which is termed as apical dominance.

So, the correct answer is 'IAA'

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Phytohormone A causes apical dominance while phytohormone B overcomes the same. Select the option that correctly identifies A and B.

  1. A-Auxin, B-Cytokinin

  2. A-Cytokinin, A-Auxin

  3. A-Gibberellin, B-Cytokinin

  4. A-Auxin, B-Gibberellin
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Presence of cytokinin in an area causes preferential movement of nutrients towards it. When applied to lateral buds, they help in their growth despite the presence of apical bud. They thus act antagonistically to auxin which promotes apical dominance. Therefore, cytokinin can overcome apical dominance, caused by auxins.

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Auxin and cytokinin are antagonistic in which of the following functions?

  1. Cell division

  2. Phototropism

  3. Apical dominance

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

Auxins are produced in the apical buds and they inhibit the growth of lateral buds on the stem thus leading to apical dominance. Whereas cytokinins promote the growth of lateral buds over and above the apical buds thereby antagonising the action of auxins.
So, the correct answer is, 'Apical dominance'.

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Apical dominance is the function of Auxin.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Apical dominance is the condition in which an apical bud grows taller as compared to the other lateral branches. This is cause because apical bud produces IAA (Indole Acetic Acid) an auxin hormone in abundance. The presence of high concentration of auxin in the apical bud causes the lateral buds to remain dormant. It has been found that if apical bud is removed, the auxin concentration decreases which allows the lateral branches to grow. 

Thus, the correct answer is option A. 

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology
Apical dominance - Auxin; Reversal of dwarfism - Gibberellins 

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Auxins are present in high concentrations in the tip of apical bud and their presence inhibits the growth of lower buds and branches. Thus one shoot becomes the tallest stem and other remain lower. This type of growth shown by apical bud in herbaceous plants is known as apical dominance. 

The major function of gibberellins is stem elongation causing the plants to grow taller. Gibberellins are responsible for increase in the internodal length in some genetically dwarf varieties such as Pea, Maize. 
Thus, the correct answer is option A. 

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

The phenomenon of apical dominance is strenthened by

  1. Removal of the tiip

  2. Removal of leaves

  3. Auxin production

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Auxin is an important plant hormone with a wide variety of effects. Auxin produced by the apical meristems inhibits the sprouting of lateral buds, and this phenomenon is called apical dominance. Apical dominance refers to an event in which the main stem of the plant grows more dominantly than the other branches on the stems. Production of auxin strengthens the phenomenon of apical dominance. Auxin inhibits the growth of lateral bud, and thereby allow the central stem to grow more vigorously.

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Apical dominance means

  1. Suppression of growth of apical bud by axillary buds .

  2. Supression of growth of axillary buds by the presence of apical bud.

  3. Stimulation of growth of axillary buds by removal of apical bud.

  4. Inhibition of growth of axillary buds by removal of the apical bud.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Apical dominance is the phenomenon where the apical bud (the main growing tip) inhibits the growth of lateral (axillary) buds through the production of auxins.

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Name the plant hormone associated with apical dominance.

  1. Auxin

  2. Ethylene

  3. Cytokinin

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  • Apical dominance is a phenomenon wherby, the inhibition of the growth of lateral buds occurs due to the terminal bud of a shoot.
  • It is caused by the production of IAA (auxin) in abundance by the apical bud.
  • This auxin is transported basipetally from the apical bud.
  • The auxin causes the lateral buds to remain dormant. 
Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Avena coleoptile test to find out the amount of growth promoting hormones was discovered by

  1. F W. Went

  2. LJ.Odum

  3. K.V Thimann

  4. F. Skoog
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

F. W. Went in 1928 used tip of Avena coleoptile. He removed the tip of Avena coleoptile and and placed in on the agar agar block for the definite measured amount of time. Then this agar agar block was placed asymmetrically on the stump, this showed a positive curvature. 

When this agar agar block was placed centrally on the stump then the growth of the coleoptile was found to be renewed. He named this growth promoting substance or hormone as auxin. 
He also noticed that curvature in Avena coleoptile is proportional, to the amount of auxin in agar agar block. Hence, option A is correct. 

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Growth hormone responsible for apical dominance is

  1. Auxin

  2. Cytokinin

  3. Gibberellin

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

Apical dominance is a phenomenon in which central stem is dominant and lateral stems are suppressed. It is due to plant hormones produced in the tip of the shoot. Auxin hormone is responsible for apical dominance and cytokinin hormone is responsible for breaking the apical dominance. 

Thus, the correct answer is option A.

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Substances which originate at the tip of stem and control growth elsewhere are

  1. Enzymes

  2. Hormones

  3. Vitamins

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A chemical substance produced in one part of body and regulates the activity of other parts is called as hormones. Plant hormones are produced in the stem, bud and root tips and control the plant growth, formation of flowers, stems, leaves, development, and ripening of fruit, etc. Auxins are specialized hormones which acts on the tip.

Thus, the correct answer is option B.