Plant Growth and Development – Plant Growth Regulators: NEET MCQs with Answers

15 free questions on Plant Growth and Development – Plant Growth Regulators for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Plant Growth Regulators: auxin, gibberellin, cytokinin, ethylene, ABA

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Question 1

Previous-year question
Consider the following statements about plant growth regulators and choose the option that gives the correct set of statements. [Re-NEET 2024]
A. All GAs are acidic in nature.
B. Auxins are antagonists to GAs.
C. Zeatin was isolated from coconut milk.
D. Ethylene induces flowering in mango.
E. Abscisic acid induces parthenocarpy.
  1. A, C, D
  2. B, E
  3. A, B, C
  4. B, D, E
Show answer
Answer: (A) A, C, D
Explanation: All GAs are acidic (A correct); zeatin was isolated from coconut milk (C correct); and ethylene induces flowering in mango (D correct). B is wrong because ABA, not auxin, acts as an antagonist to GAs, and E is wrong because auxins and gibberellins, not ABA, induce parthenocarpy.

Question 2

Previous-year question
Match List-I with List-II and choose the correct answer from the options given below. [Re-NEET 2024]
List-I:
A. Abscisic acid
B. Ethylene
C. Gibberellin
D. Cytokinin
List-II:
I. Promotes female flowers in cucumber
II. Helps seeds to withstand desiccation
III. Helps in nutrient mobilisation
IV. Promotes bolting in beet, cabbage etc.
  1. A-II, B-III, C-IV, D-I
  2. A-III, B-II, C-I, D-IV
  3. A-II, B-I, C-IV, D-III
  4. A-II, B-I, C-III, D-IV
Show answer
Answer: (C) A-II, B-I, C-IV, D-III
Explanation: Abscisic acid helps seeds withstand desiccation (A–II); ethylene promotes female flowers in cucumber (B–I); gibberellins promote bolting in beet and cabbage (C–IV); and cytokinins help in nutrient mobilisation (D–III).

Question 3

Previous-year question
F. Skoog found that internodal segments of tobacco stem formed proliferating callus when auxin was supplied together with any one of the following, except: [Re-NEET 2024]
  1. Extract of vascular tissues
  2. Coconut milk
  3. Abscisic acid
  4. Yeast extract
Show answer
Answer: (C) Abscisic acid
Explanation: Skoog and co-workers observed that tobacco internodal segments proliferated into callus only if, besides auxin, the medium was supplemented with extracts of vascular tissues, yeast extract, coconut milk or DNA, which supply cytokinin-like activity. Abscisic acid is a growth inhibitor and does not promote callus proliferation.

Question 4

Previous-year question
Match List-I with List-II and choose the correct answer from the options given below. [NEET (Sawaimadhopur) 2024]
List-I:
A. Ethylene
B. Cytokinins
C. ABA
D. Gibberellins
List-II:
I. Increase length of stem
II. Promotion of senescence and abscission
III. Delaying leaf senescence
IV. Inhibition of seed germination
  1. A–II, B–III, C–IV, D–I
  2. A–IV, B–II, C–I, D–III
  3. A–III, B–IV, C–I, D–II
  4. A–III, B–I, C–IV, D–II
Show answer
Answer: (A) A–II, B–III, C–IV, D–I
Explanation: Ethylene promotes senescence and abscission (A–II); cytokinins delay leaf senescence (B–III); ABA inhibits seed germination (C–IV); and gibberellins increase stem length (D–I).

Question 5

Previous-year question
Match List-I with List-II and choose the correct answer from the options given below. [NEET (Manipur) 2023]
List-I:
(A) Auxin
(B) Gibberellin
(C) Cytokinin
(D) Ethylene
List-II:
(I) Promotes female flower formation in cucumber
(II) Overcoming apical dominance
(III) Increase in the length of grape stalks
(IV) Promotes flowering in pineapple
  1. (A)-(II), (B)-(I), (C)-(IV), (D)-(III)
  2. (A)-(IV), (B)-(III), (C)-(II), (D)-(I)
  3. (A)-(I), (B)-(III), (C)-(IV), (D)-(II)
  4. (A)-(III), (B)-(II), (C)-(I), (D)-(IV)
Show answer
Answer: (B) (A)-(IV), (B)-(III), (C)-(II), (D)-(I)
Explanation: Auxins induce flowering in pineapple (A–IV); gibberellins increase the length of grape stalks (B–III); cytokinins help overcome apical dominance (C–II); and ethylene promotes female flowers in cucumber (D–I).

Question 6

Previous-year question
Which of the following plant growth regulators is derived from adenine? [Re-NEET 2022]
  1. Auxin
  2. Cytokinin
  3. Ethylene
  4. Abscisic acid
Show answer
Answer: (B) Cytokinin
Explanation: Cytokinins such as kinetin (N⁶-furfurylaminopurine) and zeatin are adenine (purine) derivatives. Auxins are indole compounds, ethylene is a gas, and abscisic acid is a carotenoid (terpenoid) derivative.

Question 7

Previous-year question
Removing apical dominance by cutting off the shoot apex (decapitation) is made use of in: [NEET (Overseas) 2022]
  1. Early senescence
  2. Hedge making
  3. Preparing weed-free lawns
  4. Suppressing the activity of intercalary meristem
Show answer
Answer: (B) Hedge making
Explanation: Decapitation removes the auxin-mediated apical dominance, so lateral buds sprout and the plant becomes bushy; this is widely used in hedge making and tea plantations. Weed-free lawns are prepared with 2,4-D, and decapitation neither causes senescence nor suppresses intercalary meristems.
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Question 8

Previous-year question
Which of the following scientist–hormone pairs is matched incorrectly? [NEET (Paper-2) 2021]
  1. Ethylene – Cousins
  2. Kinetin – Skoog and Miller
  3. Gibberellic acid – F.W. Went
  4. Auxin – Darwin and Darwin
Show answer
Answer: (C) Gibberellic acid – F.W. Went
Explanation: Gibberellic acid was discovered by E. Kurosawa from the 'bakanae' (foolish seedling) disease of rice caused by Gibberella fujikuroi; F.W. Went isolated auxin from oat coleoptile tips. The other pairs are correct: Cousins (ethylene), Skoog and Miller (kinetin), Charles and Francis Darwin (auxin).

Question 9

Previous-year question
The term 'kinetin' was coined by whom? [NEET (COVID-19) 2020]
  1. Skoog and Miller
  2. Darwin
  3. Went
  4. Kurosawa
Show answer
Answer: (A) Skoog and Miller
Explanation: Skoog and Miller identified and crystallised the cytokinesis-promoting active substance (from autoclaved herring sperm DNA) and named it kinetin. Darwin and Went are associated with auxin, and Kurosawa with gibberellins.

Question 10

Previous-year question
Name the plant growth regulator which, on spraying on a sugarcane crop, increases the length of the stem and thus increases the yield of the sugarcane crop. [NEET 2020]
  1. Gibberellin
  2. Ethylene
  3. Abscisic acid
  4. Cytokinin
Show answer
Answer: (A) Gibberellin
Explanation: Gibberellin causes a marked elongation of the internodes. Since sugarcane stores its sugar in the stem, lengthening the stem directly increases the sugar yield of the crop.

Question 11

Previous-year question
It takes a very long time for pineapple plants to produce flowers. Which combination of hormones can be applied to induce flowering artificially in pineapple plants throughout the year to increase the yield? [NEET 2019]
  1. Auxin and ethylene
  2. Gibberellin and cytokinin
  3. Gibberellin and abscisic acid
  4. Cytokinin and abscisic acid
Show answer
Answer: (A) Auxin and ethylene
Explanation: Auxins such as NAA initiate flowering and synchronise fruit set in pineapple, and ethylene (usually supplied as ethephon) does the same. Applying the two together allows the crop to be flowered and harvested at any time of the year.

Question 12

Previous-year question
Fruit and leaf drop at early stages can be prevented by the application of [NEET 2017]
  1. ethylene
  2. auxins
  3. gibberellic acid
  4. cytokinins
Show answer
Answer: (B) auxins
Explanation: Auxins prevent the abscission of young fruits and leaves by maintaining a high auxin concentration on the distal side of the abscission zone. Paradoxically, the same hormones promote the abscission of older, mature leaves and fruits.

Question 13

Previous-year question
The Avena curvature test is used for the bioassay of [NEET 2016]
  1. ABA
  2. GA₃
  3. IAA
  4. ethylene
Show answer
Answer: (C) IAA
Explanation: In the Avena curvature test, an agar block containing the hormone is placed asymmetrically on a decapitated oat coleoptile and the angle of curvature is measured. It is specific for auxins, of which IAA is the natural representative.

Question 14

Previous-year question
What causes a green plant exposed to light on only one side to bend towards the source of light as it grows? [AIPMT 2015]
  1. Green plants seek light because they are phototropic
  2. Light stimulates plant cells on the lighted side to grow faster
  3. Auxin accumulates on the shaded side, stimulating greater cell elongation there
  4. Green plants need light to perform photosynthesis
Show answer
Answer: (C) Auxin accumulates on the shaded side, stimulating greater cell elongation there
Explanation: Unilateral light causes the lateral redistribution of auxin in the coleoptile tip, so that more auxin reaches the shaded side. The cells there elongate faster than those on the illuminated side, and the shoot curves towards the light.

Question 15

Previous-year question
Auxin can be bioassayed by [AIPMT 2015]
  1. hydroponics
  2. a photometer
  3. lettuce hypocotyl elongation
  4. Avena coleoptile curvature
Show answer
Answer: (D) Avena coleoptile curvature
Explanation: The Avena coleoptile curvature test devised by F.W. Went is the classical bioassay for auxin, the angle of bending being proportional to the amount of auxin present. The lettuce hypocotyl elongation test is a bioassay for gibberellins.

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