All four chemical classifications (i: Indole, ii: Adenine derivative, iii: Terpene, iv: Carotenoid derivative) are correct.
Question 22 of 100
📘 CLASS XI
Categorize PGRs into plant growth promoters and inhibitors based on their primary functions:
(i) Auxins, gibberellins, and cytokinins are plant growth promoters involved in cell division, enlargement, pattern formation, and tropic growth. (ii) Abscisic acid (ABA) plays an important role in growth inhibiting activities such as dormancy and abscission. (iii) Ethylene is a gaseous PGR that is largely an inhibitor of growth activities. (iv) Cytokinins act exclusively as growth inhibitors during seed germination.
Statements (i), (ii), and (iii) are correct because auxins, gibberellins, and cytokinins are promoters, ABA is an inhibitor, and ethylene is largely inhibitory. Statement (iv) is incorrect because cytokinins are growth promoters.
Question 23 of 100
📘 CLASS XI
Regarding the discovery of auxins, consider the following historical experiments:
(i) Charles Darwin and Francis Darwin observed canary grass coleoptiles responding to unilateral illumination by bending towards light. (ii) The tip of the coleoptile was demonstrated to be the site of transmittable influence. (iii) Auxin was first isolated by F.W. Went from tips of coleoptiles of oat (Avena) seedlings. (iv) F.W. Went isolated auxin directly from the endosperm of maize seeds.
Statements (i), (ii), and (iii) accurately describe Darwin's phototropism experiments and F.W. Went's isolation of auxin from oat coleoptile tips. Statement (iv) is incorrect because Went isolated auxin from oat coleoptile tips.
Question 24 of 100
📘 CLASS XI
Examine the discovery of gibberellins and the bakanae disease:
(i) Bakanae (foolish seedling) disease of rice seedlings was caused by the fungal pathogen Gibberella fujikuroi. (ii) E. Kurosawa (1926) reported disease symptoms in rice seedlings treated with sterile filtrates of the fungus. (iii) The active substance in the fungal filtrate was later identified as gibberellic acid. (iv) E. Kurosawa proved that bakanae disease was caused by a viral infection.
Statements (i), (ii), and (iii) are correct regarding fungal origin (Gibberella fujikuroi), Kurosawa's 1926 discovery, and gibberellic acid. Statement (iv) is incorrect because it is caused by a fungus, not a virus.
Question 25 of 100
📘 CLASS XI
Regarding the discovery of cytokinins, evaluate the following experimental observations:
(i) F. Skoog and co-workers observed tobacco stem internodal callus proliferated with auxin plus vascular extract, yeast extract, coconut milk, or DNA. (ii) Miller et al. (1955) identified and crystallized the cytokinesis-promoting substance kinetin. (iii) Kinetin was isolated from autoclaved herring sperm DNA. (iv) Kinetin is a naturally occurring cytokinin synthesized abundantly in plant shoots.
Statements (i), (ii), and (iii) are correct regarding Skoog's tissue culture observations and Miller's isolation of kinetin from herring sperm DNA. Statement (iv) is incorrect because kinetin does not occur naturally in plants.
Question 26 of 100
📘 CLASS XI
Examine the discovery of Abscisic Acid (ABA) and Ethylene:
(i) During mid-1960s, three independent research groups reported inhibitor-B, abscission II, and dormin. (ii) All three inhibitors were proved to be chemically identical and named abscisic acid (ABA). (iii) H.H. Cousins (1910) confirmed release of a volatile substance from ripened oranges that hastened banana ripening. (iv) The volatile substance released from oranges was identified as liquid gibberellin.
Statements (i), (ii), and (iii) are correct regarding ABA discovery (inhibitor-B, abscission II, dormin) and Cousins' ethylene discovery from oranges. Statement (iv) is incorrect because the volatile substance was identified as ethylene, a gaseous PGR.
Question 27 of 100
📘 CLASS XI
Which of the following are natural auxins and synthetic auxins respectively?
(i) Natural auxins: Indole-3-acetic acid (IAA) and Indole butyric acid (IBA). (ii) Synthetic auxins: Naphthalene acetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-D). (iii) Auxins were first isolated from human urine. (iv) IAA and IBA are synthetic auxins synthesized exclusively in chemical laboratories.
Statements (i), (ii), and (iii) are correct because IAA and IBA are natural auxins, NAA and 2,4-D are synthetic, and auxins were first isolated from human urine. Statement (iv) is incorrect because IAA and IBA are natural auxins isolated from plants.
Question 28 of 100
📘 CLASS XI
Analyze the agricultural and horticultural applications of auxins:
(i) Auxins help initiate rooting in stem cuttings for plant propagation. (ii) Auxins promote flowering in pineapples. (iii) Auxins prevent fruit and leaf drop at early stages but promote abscission of older mature leaves and fruits. (iv) Auxins induce abscission of young developing fruits in early spring.
Statements (i), (ii), and (iii) accurately describe auxin applications. Statement (iv) is incorrect because auxins prevent fruit and leaf drop at early stages.
Question 29 of 100
📘 CLASS XI
Consider the physiological mechanism of apical dominance in plants:
(i) The growing apical bud inhibits the growth of lateral (axillary) buds. (ii) Removal of shoot tips (decapitation) usually results in the growth of lateral buds. (iii) Decapitation is widely applied in tea plantations and hedge-making. (iv) Cytokinins act synergistically with auxins to maintain strict apical dominance.
Statements (i), (ii), and (iii) are correct regarding apical dominance, decapitation, and tea plantation/hedge applications. Statement (iv) is incorrect because cytokinins help overcome apical dominance, acting antagonistically to auxin in this process.
Question 30 of 100
📘 CLASS XI
Evaluate the specific uses of auxins in weed control and tissue differentiation:
(i) Auxins induce parthenocarpy in tomatoes. (ii) 2,4-D is widely used as a herbicide to kill dicotyledonous weeds. (iii) 2,4-D does not affect mature monocotyledonous plants, making it ideal for weed-free lawns. (iv) Auxin controls xylem differentiation and helps in cell division.
All four statements (i), (ii), (iii), and (iv) are correct regarding tomato parthenocarpy, 2,4-D selective dicot weed control sparing monocots, xylem differentiation, and cell division.
