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

Apical dominance in higher plants is due to

  1. photoperiodism.

  2. enzymes.

  3. carbohydrates.

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

Apical dominance is the phenomenon whereby the main central stem of the plant is dominant over (i.e. grows more strongly than) other side stems; on a branch, the main stem of the branch is further dominant over its own side branchlets. It occurs in higher plants due to hormones auxin, which is responsible for apical dominance, and cytokinin, which is responsible for breaking of apical dominance.

Multiple choice

Phloem carries hormones in _________ of plants.

  1. roots

  2. stems

  3. shoot tips

  4. both (1) and (2)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Phloem transports hormones and organic nutrients throughout the plant, moving bidirectionally. This transport occurs through all plant parts including roots, stems, and shoot tips.

Multiple choice

Which one of the following is produced during water stress and causes closure of stomata?

  1. Abscisic acid

  2. Auxin

  3. Gibberellin

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

Abscisic acid (ABA, Option A) is a plant hormone produced during water stress conditions. It accumulates in guard cells and triggers stomatal closure to prevent further water loss. This is a crucial drought response mechanism. Auxin (B) and Gibberellin (C) are growth hormones. Ethylene (D) is involved in fruit ripening and stress responses but not primarily in stomatal closure.

Multiple choice

What are morphactins?

  1. Growth retardants

  2. Synthetic growth regulators

  3. Phytochromes

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

Morphactins include several synthetic fluorine-containing compounds that tend to produce morphological changes and suppress the growth in plants.

Multiple choice

How does pruning of plants promote branching?

  1. The activity of ethylene decreases.

  2. Auxiliary buds get sensitised to gibberellin.

  3. Auxiliary buds get sensitised to cytokinin.

  4. The activity of abscisic acid decreases.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Auxin is synthesised in apical meristems of shoots. 

Multiple choice

Which of the following statements are correct or wrong?

a. The origin of parts or organs and the gross form of the plant is called morphogenesis. b. The annual plants show unlimited growth. c. Growth regulators are organic substances synthesised in the plant parts. d. The pattern of growth is sigmoid in plants or plant parts.

  1. a and c are correct.

  2. a and d are correct.

  3. b and d are wrong.

  4. c and d are wrong.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The correct answer is option 2.

Multiple choice

Gibberellins induce flowering under non-inductive conditions mainly in long day plants but are reported to induce flowering in some short day plants also. Which of the following plants is included in that category?

  1. Xanthium

  2. Impatiens balsamina

  3. Dahlia

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

Impatiens balsamina is a well-documented short-day plant that responds to gibberellin treatment by flowering under non-inductive conditions. While Xanthium, Dahlia, and Biloxi soybean are all short-day plants, Impatiens balsamina is specifically mentioned in botanical literature as responding to gibberellins for flowering induction, making it the correct answer.

Multiple choice

Avena coleoptile bioassay is used for detection of

  1. gibberellins

  2. cytokinins

  3. auxins

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

The Avena coleoptile curvature test is a specific bioassay developed by F.W. Went and others to detect and quantify auxins (indole-3-acetic acid and related compounds). When auxin is applied asymmetrically to a decapitated oat coleoptile, it causes cell elongation and curvature proportional to the auxin concentration. This test is not specific for gibberellins, cytokinins, or abscisic acid, which have different bioassays.