Q20. Spraying which phytohormone on juvenile conifers helps hasten maturity and early seed production?
[NEET 2023]
(A) Gibberellic acid
(B) Zeatin
(C) Abscisic acid
(D) Indole-3-butyric acid
Answer: (A) Gibberellic acid
Explanation: Gibberellic acid can hasten the transition to reproductive maturity in some juvenile conifers and may promote earlier cone and seed formation. It is valuable in forestry seed production. Zeatin is a cytokinin, abscisic acid favours dormancy, and indole-3-butyric acid commonly promotes rooting.
Q19. Which plant growth regulator is an adenine derivative?
[NEET 2022, Phase 2]
(A) Abscisic acid
(B) Auxin
(C) Cytokinin
(D) Ethylene
Answer: (C) Cytokinin
Explanation: Many cytokinins, including kinetin and zeatin, are derivatives of the purine base adenine. Their principal effects include promoting cell division and delaying leaf senescence. Auxins such as IAA are indole-related compounds, while ethylene is a simple gaseous molecule.
Q18. Which phytohormone can increase cucumber yield by promoting female flower formation?
[NEET 2022, Phase 1]
(A) Abscisic acid
(B) Gibberellin
(C) Ethylene
(D) Cytokinin
Answer: (C) Ethylene
Explanation: Ethylene promotes femaleness in cucurbits such as cucumber. Increasing the proportion of female flowers can improve fruit set because fruits develop from female flowers. Ethephon is often used as an ethylene-releasing compound, but its application must suit the crop and conditions.
Q17. A student wants to increase cell division in plants. Which plant hormone should be recommended?
[UPSC CDS-I 2021]
(A) Abscisic acid
(B) Gibberellins
(C) Cytokinin
(D) Auxin
Answer: (C) Cytokinin
Explanation: Cytokinins are especially associated with cytokinesis and cell proliferation. They are frequently used with auxins in plant tissue culture to control callus growth and organ formation. Auxins primarily influence cell elongation and rooting, while gibberellins favour elongation and seed germination.
Q16. Which plant hormone helps in the growth of plant stems?
[RRB NTPC CBT-I, 14 March 2021, Shift 2]
(A) Abscisic acid
(B) Cytokinin
(C) Ethylene
(D) Gibberellin
Answer: (D) Gibberellin
Explanation: Gibberellins are well known for promoting internode elongation and increasing plant height. They also help some seeds overcome dormancy and can induce bolting in rosette plants. Abscisic acid has largely opposing effects on germination, while ethylene regulates diverse growth responses.
Q15. Which plant hormone regulates growth particularly by stimulating cell elongation in stems?
[SSC CGL 2020 Tier-I, held 23 August 2021, Shift 1]
(A) Ethylene
(B) Auxin
(C) Gibberellin
(D) Cytokinin
Answer: (B) Auxin
Explanation: Auxins such as indole-3-acetic acid stimulate elongation of young shoot cells through processes including cell-wall loosening. They also help establish apical dominance and directional growth responses. Gibberellins promote stem elongation too, but the question specifically identifies the classic auxin function.
Q14. Which of the following is not a plant hormone?
[RRB NTPC CBT-I, 7 March 2021, Shift 2]
(A) Gibberellins
(B) Prolactin
(C) Ethylene
(D) Abscisic acid
Answer: (B) Prolactin
Explanation: Prolactin is secreted mainly by the anterior pituitary in animals and is important for lactation. Gibberellins, ethylene and abscisic acid are plant hormones. Ethylene regulates ripening, gibberellins stimulate elongation and germination, and abscisic acid helps maintain dormancy.
Q13. Leaf fall generally becomes more likely when which hormonal change occurs in the leaf?
[UPPSC GIC Lecturer Biology 2021]
(A) The amount of auxin decreases
(B) The amount of auxin increases
(C) The amount of abscisic acid decreases
(D) The amount of gibberellic acid decreases
Answer: (A) The amount of auxin decreases
Explanation: Auxin supplied by a healthy leaf helps maintain its attachment to the stem. As a leaf ages, lower auxin supply can make the abscission zone more responsive to ethylene, allowing separation. Thus declining auxin is associated with leaf fall.
Q12. Which combination of hormones can help induce flowering in pineapple throughout the year?
[NEET 2019]
(A) Gibberellin and abscisic acid
(B) Cytokinin and abscisic acid
(C) Auxin and ethylene
(D) Gibberellin and cytokinin
Answer: (C) Auxin and ethylene
Explanation: Ethylene is an important inducer of flowering in pineapple, and auxin-based treatments may also help trigger flowering through ethylene-related responses. Controlled flowering allows growers to coordinate crop production. Gibberellins and abscisic acid are not the standard combination identified here.
Q11. Sub-apical elongation in plants is induced mainly by which hormone?
[RPSC Senior Teacher Grade II Science, 1 November 2018]
(A) Auxins
(B) Gibberellins
(C) Cytokinin
(D) Ethylene
Answer: (B) Gibberellins
Explanation: Gibberellins strongly stimulate elongation of the sub-apical region and stem internodes. They are especially important in bolting and the growth of certain dwarf varieties. Auxin promotes cell elongation in shoots but gibberellin is the intended regulator for the described sub-apical response.
