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 biology plant growth seed dormancy fruit plants: structure and function

Among the following which compound can induce seed dormancy?

  1. Gibberellins

  2. Caffeine

  3. ABA

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

Abscisic acid (ABA) is the primary plant hormone responsible for inducing and maintaining seed dormancy to prevent premature germination.

Multiple choice biology plant growth seed dormancy fruit plants: structure and function

State whether the following statements are true or false.
In a plant seedling exposed to light on only one side, auxin produced in the tip moves to the lighted side and inhibits growth of cells there.

  1. True

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

When the light is exposed to only one side of the seedling, the auxin will move and grow towards the side of the light. This phenomenon is termed as phototropism (Movement of plant growth towards the source of light). Thus only one seed of the seedling will be able to grow and the other where light is unable to reach will not grow.

So, the correct statement is 'False'.

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

Apical dominance in higher plants is due to 

  1. Enzyme activity

  2. Photoperiodism

  3. Carbohydrate-nitrogen ratio

  4. Balance between auxin and cytokinins
Reveal answer Fill a bubble to check yourself
D 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. Hence, apical dominance depends on the auxin to cytokinin balance. 

Thus, the correct answer is option D.

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

Study the following statements and select the correct ones.

  1. Auxin is transported from base to tip in large quantities.

  2. Cells on the dark side expand farther than those on the light side.

  3. Apical dominance can be removed the decapitation

  4. Tropic movements in plants are under the control of gibberellins
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Decapitation involves cutting of apical bud in plants. When the apical bud is removed, the source of auxin is removed. Auxin causes apical dominance. Since the auxin concentration is much lower, the lateral buds can now grow. In fact, their growth will be stimulated by a relatively small drop in auxin concentration. Thus, decapitating a shoot will cause it to branch.

So, the correct option is 'Apical dominance can be removed the decapitation'.

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

Which growth hormone is responsible for apical dominance?

  1. Auxin

  2. Cytokinin

  3. Gibberellin

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

Auxin exerts profound effects on plants. For example, some plants tend to branch out very little when they grow. Growth in these plants occurs almost exclusively from the apical meristem rather than from axillary buds, which do not develop as long as the terminal bud is present. Such plants are said to exhibit apical dominance, the inhibition of axillary bud growth by the apical meristem. In plants with strong apical dominance, auxin produced in the apical meristem inhibits axillary buds near the apical meristem from developing into actively growing shoots. When the apical meristem is pinched off, the auxin source is removed and axillary buds grow to form branches. Apical dominance is often quickly re-established, however, as one branch begins to inhibit the growth of others.

Thus, the correct answer is option A.

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

How does pruning help in making the hedge dense?

  1. It releases wound hormones.

  2. It induces the differentiation of new shoots from the rootstock.

  3. It frees auxillary buds from apical dominance.

  4. The apical shoot grows faster after pruning.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Auxin is the phytohormone which is responsible for promoting apical dominance in plants. Auxin is usually seen at the growing tips of plants. Thus the auxin present at the tip of plants will be channelized sidewards, lateral meristem; so that the plants will not grow tall but instead becomes bushy in nature.

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

Which of the following is responsible for apical dominance ?

  1. GA$ _3$

  2. IAA

  3. ABA

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

Auxins promote elongation of stem and coleoptile. It promotes the growth by the elongation of cells in the apical meristem. Growth in the lateral bud is inhibited when the apical bud of a tall plant remains intact. However, the lateral bud grows rapidly on the removal of apical bud. Suppression of growth in the lateral bud by apical bud due to auxin produced by apical bud is termed as apical dominance. IAA is an example of auxin. 

Thus, the correct answer is option B. 

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

Which hormone is responsible for apical growth?

  1. IAA

  2. ABA

  3. GA

  4. All of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Auxins (like IAA) and gibberellins (GA) are growth promoting phytohormones. IAA promotes apical growth whereas GA causes internodal elongation. Promotion of apical growth by auxins and suppression of axillary growth is also called as apical dominance.

Thus, the correct answer is option A.

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

Apical dominance is not affected by

  1. Indole acetic acid

  2. Gibberellin

  3. Indoleacetaldehyde

  4. Indole-3-butyric acid
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Apical dominance is a physiological response of auxins. The chemicals mentioned in options A, C and D are all auxins. They inhibit the growth of axillary buds and stimulate the growth of apical bud. This phenomenon is called as apical dominance. Gibberellins are also growth promoting phytohormones. They stimulate internodal elongation. Thus, bringing about an increase in length or height of plants.

Thus, the correct answer is option B.

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

I. Assertion: The presence of apical bud inhibits the growth of lateral bud, this is called apical dominance.
II. Reason: Auxin is responsible for apical dominance.

  1. I and II both are wrong

  2. I is wrong and II is correct

  3. I and II both are correct , II is correct explanation for I

  4. I and II both are correct , II is not a correct explanation for I
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Auxins when applied to plant cuttings help in formation of adventitious roots. Higher concentration of auxin at apical bud suppresses growth of lateral bud having low concentration of auxin.

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

Apical dominance is not affected by ...................

  1. Indole acetic acid

  2. Gibberellic acid

  3. Indole acetaldehyde

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

GA promotes the elongation of plants by inducing the division of lateral meristem. Whereas, the phytohormone auxin causes the apical dominance in plants. In the given options all other options other than gibberellic acid accounts for different types of auxin.

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

A potted plant placed near the window bends outwardly due to 

  1. Greater oxygen availability to the tip.

  2. More auxin content on the shaded side.

  3. Greater light availability to tip.

  4. Availability of necessary warmth to the tip.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Greater growth on the shaded side of the stem is due to more accumulation of auxin on the shaded  side than on the illuminates. Auxin causes bending of plant towards light. Phototropism is induced by auxin hormone.