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

Which plant hormone is synthesized in shoot tips?

  1. Auxin

  2. Cytokinin

  3. Abscisic acid

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

Auxin is synthesised in shoot tips. Indole-3-acetic acid (IAA) is the most abundant and the basic auxin natively occurring and functioning in plants. It generates the majority of auxin effects in intact plants, and is the most potent native auxin.

Multiple choice

Which of the following statements are true regarding gibberellins? P. Gibberellin was named after the fungus gibberella africana. Q. Gibberellins are chemically terpenoid derivatives. R. Gibberellic acid is a dihydroxylated gibberellin. S. GA1 was the first gibberellin to be structurally characterized. Select the correct answer using codes given below:

  1. P and Q

  2. P and R

  3. P and S

  4. Q and R

  5. R and S
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Gibberellin was named after the fungus gibberella fujikuroi. Gibberellin was first isolated in 1935 by Teijiro Yabuta and Sumuki, from fungal strains (gibberella fujikuroi). Gibberellic acid (GA3) was the first gibberellin to be structurally characterized.

Multiple choice

Identify the false statement(s).

  1. Regulation of cell cycle progression depends on cyclin dependent kinase (CDK) and protease activity.
  2. Photorespiratory reaction occurring in oxidative photosynthetic carbon (C2) pathway involves a cooperative interaction among three organelles: chloroplast, peroxisome and mitochondria.
  3. Cytokinins acts as a promoter of senescence and ethylene act as a senescence antagonist.

  1. Only 1

  2. Only 2

  3. Only 3

  4. Both 1 and 2

  5. Both 2 and 3
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Correct answer. Ethylene acts as a promoter of senescence and cytokinins act as a senescence antagonist.

Multiple choice

Which of the following is a stress hormone?

  1. Benzyl aminopurine

  2. Dichloro acetic acid

  3. Abscisic acid

  4. Auxin

  5. Oxaloacetic acid
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

It promotes leaf detachment which induces dormancy and inhibits germination.

Multiple choice

Which of the following are examples of natural plant growth regulators?

i. IAA ii. GA3 iii. Zeatin iv. 2,4-D v. IBA

  1. Only i, ii and iii

  2. Only i, iv and v

  3. Only ii and iv

  4. Only iii and v

  5. Only iii, iv and v
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

All are natural plant growth regulators. Indole-3-acetic acid (IAA) is the most common, naturally-occurring, natural plant growth regulator hormone of the auxin class. Gibberellic Acid (GA3) is an important natural plant growth regulator that is used commercially to increase plant growth and crop yields. Zeatin is a member of the plant growth regulator hormone family known as cytokinins.

Multiple choice

Vernalisation can be replaced by

  1. cytokinins

  2. ethylene

  3. gibberlins

  4. abscisic acid

  5. NA
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Vernalisation can be replaced by Gibberlins. They are acidic in nature and its application increases the sugar yield by promoting internodal growth. Hence, it is the correct answer.

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.