Gibberellins and Bakanae Disease — NEET Biology

Correct answer: A — S1 and S4 only

The question asks for statements that are NOT correct regarding plant growth and development, specifically focusing on PGRs and regulatory factors. S1: "Plant growth regulators are small, simple molecules of diverse chemical composition that are always synthesised in large amounts." This statement is NOT correct. While PGRs are small, simple molecules of diverse chemical composition (NCERT Page 174, Section 13.4.1), they are not always synthesised in large amounts. The NCERT context implies their regulatory role even in small concentrations, and the text does not state they are *always* synthesised in large amounts. In fact, they act as signals, often implying effectiveness at low concentrations. S2: "Ethylene can be broadly categorised as a plant growth inhibitor, although it may promote certain growth activities." This statement is correct. NCERT states, "The gaseous PGR, ethylene, could fit either of the groups, but it is largely an inhibitor of growth activities." (Page 174, Section 13.4.1). It also promotes root growth and internode elongation in deep water rice (Page 177, Section 13.4.3.4). S3: "The first gibberellins were discovered from a fungal pathogen, and all known gibberellins are acidic compounds." This statement is correct. NCERT states, "The ‘bakanae’ (foolish seedling) disease of rice seedlings, was caused by a fungal pathogen Gibberella fujikuroi. E. Kurosawa (1926) reported the appearance of symptoms of the disease... The active substances were later identified as gibberellic acid." (Page 175, Section 13.4.2). It also states, "All GAs are acidic." (Page 176, Section 13.4.3.2). S4: "Plant development is solely regulated by intrinsic factors like plant growth regulators and genetic control, with no significant environmental influence." This statement is NOT correct. NCERT explicitly states, "Development in plants (i.e., both growth and differentiation) is under the control of intrinsic and extrinsic factors." (Page 174, Section 13.3, last paragraph). Extrinsic factors include light, temperature, water, oxygen, nutrition, etc. S5: "Cytokinins play a role in overcoming apical dominance, promoting nutrient mobilisation, and delaying leaf senescence." This statement is correct. NCERT states, "Cytokinins help overcome the apical dominance. They promote nutrient mobilisation which helps in the delay of leaf senescence." (Page 177, Section 13.4.3.3). Therefore, statements S1 and S4 are NOT correct. The final answer is A because S1 and S4 are the incorrect statements. This question tests the understanding of PGR characteristics, their classification, discovery, specific functions, and the overall control of plant development by both intrinsic and extrinsic factors.