Sample 1Easy
Which of the following plant growth regulators is a gas?
- A
Abscisic acid
- B
Gibberellic acid
- C
Cytokinin
- D
Ethylene
Show the answer
The answer is D.Ethylene is a simple gaseous plant growth regulator. Auxins, gibberellins, cytokinins and abscisic acid are not gases.
- A.
Abscisic acid is a derivative of carotenoids, not a gas.
- B.
Gibberellic acid is a terpene, not a gas.
- C.
Cytokinins are adenine derivatives, not gases.
NCERT: Class 11 Biology, Chapter 13 (Plant Growth and Development), Plant Growth Regulators, Ethylene
Sample 2Medium
A figure shows two potted plants of the same kind. In plant I the shoot tip is intact, and the axillary buds below it stay dormant. In plant II the shoot tip has been cut off, and the axillary buds have grown into branches. Which growth regulator produced by the shoot tip explains this difference, and where is the effect used?
- A
Auxin; in tea plantations and hedge-making
- B
Cytokinin; in tea plantations and hedge-making
- C
Gibberellin; to increase the length of sugarcane stems
- D
Ethylene; to hasten fruit ripening
Show the answer
The answer is A.The growing apical bud suppresses the lateral buds through auxin, which is called apical dominance. Removing the shoot tip lets the lateral buds grow. This is used in tea plantations and hedge-making.
- B.
Cytokinins help overcome apical dominance, so they promote lateral buds. The inhibition by the shoot tip is due to auxin.
- C.
Gibberellins elongate stems and increase sugarcane yield, but they are not the cause of apical dominance.
- D.
Ethylene promotes fruit ripening. It is not the shoot-tip regulator that suppresses the axillary buds.
NCERT: Class 11 Biology, Chapter 13
Sample 3NEET level
Match the plant growth regulators in List I with their effects in List II. List I A. Auxins B. Gibberellins C. Cytokinins D. Abscisic acid List II I. Delay leaf senescence II. Stimulate the closure of stomata III. Initiate rooting in stem cuttings IV. Increase the length of the stem in sugarcane Choose the correct answer from the options given below.
- A
A-III, B-IV, C-I, D-II
- B
A-III, B-I, C-IV, D-II
- C
A-IV, B-III, C-I, D-II
- D
A-III, B-IV, C-II, D-I
Show the answer
The answer is A.Auxins initiate rooting in stem cuttings and gibberellins increase sugarcane stem length. Cytokinins delay leaf senescence, and abscisic acid stimulates the closure of stomata.
- B.
Swaps the effects of gibberellins and cytokinins.
- C.
Swaps the effects of auxins and gibberellins.
- D.
Swaps the effects of cytokinins and abscisic acid.
NCERT: Class 11 Biology, Chapter 13 (Plant Growth and Development), Plant Growth Regulators – Physiological Effects