Examine the physiological roles of Abscisic Acid (ABA) as a general inhibitor and stress hormone:
(i) ABA acts as a general plant growth inhibitor and inhibitor of plant metabolism. (ii) ABA inhibits seed germination. (iii) ABA stimulates the closure of stomata and increases tolerance to various kinds of stresses. (iv) ABA is called the 'stress hormone' due to its role in stress tolerance.
All four statements (i), (ii), (iii), and (iv) are correct regarding ABA as a general inhibitor, germination inhibitor, stomatal closer, and stress hormone.
Question 42 of 100
📘 CLASS XI
Consider the role of ABA in seed development and its relationship with Gibberellins:
(i) ABA plays an important role in seed development, maturation, and dormancy. (ii) By inducing dormancy, ABA helps seeds withstand desiccation and unfavourable growth factors. (iii) In most situations, ABA acts as an antagonist to GAs. (iv) ABA and GAs act synergistically to promote rapid seed germination under drought stress.
Statements (i), (ii), and (iii) are correct regarding seed dormancy, desiccation tolerance, and ABA-GA antagonism. Statement (iv) is incorrect because ABA inhibits germination while GA promotes it (they are antagonists).
Question 43 of 100
📘 CLASS XI
Regarding the interactions and extrinsic control of PGRs, analyze these statements:
(i) For any phase of growth, differentiation, and development, PGR roles can be complementary or antagonistic. (ii) PGR interactions can be individualistic or synergistic. (iii) Events like seed dormancy, abscission, senescence, and apical dominance involve interaction of more than one PGR. (iv) Extrinsic factors like light and temperature control plant growth and development via PGRs.
All four statements (i), (ii), (iii), and (iv) are true statements summarizing PGR complementary/antagonistic/synergistic roles and extrinsic light/temperature control via PGRs.
Question 44 of 100
📘 CLASS XI
Which of the following processes are listed as examples of events controlled by extrinsic factors (light and temperature) via PGRs?
(i) Vernalisation and flowering. (ii) Seed germination and dormancy. (iii) Plant movements. (iv) Secondary xylem lignification during secondary thickening.
Statements (i), (ii), and (iii) are explicitly cited in the text as events controlled by extrinsic factors via PGRs. Statement (iv) is incorrect as xylem lignification is a cellular differentiation process, not an extrinsic-PGR controlled event cited in that list.
Question 45 of 100
📘 CLASS XI
Examine the summary statements on plant growth meristems and growth forms:
(i) Root and shoot apical meristems, sometimes along with intercalary meristem, contribute to elongation growth of plant axes. (ii) Growth is indeterminate in higher plants. (iii) Following cell division in root and shoot apical meristems, growth can be arithmetic or geometrical. (iv) Plant growth is sustained at a constant maximum rate throughout the entire life of an organism.
Statements (i), (ii), and (iii) are correct summary points regarding meristems, indeterminate growth, and arithmetic/geometric phases. Statement (iv) is incorrect because growth is generally not sustained at a high rate throughout life.
Question 46 of 100
📘 CLASS XI
Regarding the three principal phases of growth mentioned in the chapter summary, evaluate:
(i) The three principal phases of growth are lag phase, log phase, and senescent phase. (ii) When a cell loses the capacity to divide, it leads to differentiation. (iii) Differentiation results in development of structures commensurate with final function. (iv) A differentiated cell can never dedifferentiate or redifferentiate under any circumstances.
Statements (i), (ii), and (iii) are correct summary statements. Statement (iv) is incorrect because differentiated cells can dedifferentiate and redifferentiate.
Question 47 of 100
📘 CLASS XI
Analyze the summary statements regarding development and plasticity:
(i) Development is the sum of growth and differentiation. (ii) Since differentiation in plants is open, development is also flexible. (iii) Plants exhibit plasticity in development. (iv) Plant growth and development are under the control of both intrinsic and extrinsic factors.
All four statements (i), (ii), (iii), and (iv) are correct summary statements on development, open differentiation, plasticity, and intrinsic/extrinsic control.
Question 48 of 100
📘 CLASS XI
Which of the following correctly pairs the PGR with its specific agricultural application as asked in chapter exercises?
(i) Induce rooting in a twig: Auxin. (ii) Quickly ripen a fruit: Ethylene. (iii) Delay leaf senescence: Cytokinin. (iv) Induce immediate stomatal closure in leaves: Abscisic acid (ABA).
All four pairings (i: Auxin for rooting, ii: Ethylene for ripening, iii: Cytokinin for delaying senescence, iv: ABA for stomatal closure) are completely correct based on textbook applications.
Question 49 of 100
📘 CLASS XI
Consider the application of PGRs for specific growth modifications:
(i) Induce growth in axillary buds (overcoming apical dominance): Cytokinin. (ii) 'Bolt' a rosette plant: Gibberellin (GA). (iii) Kill dicotyledonous weeds in lawns: 2,4-D (synthetic auxin). (iv) Hasten maturity period in juvenile conifers: Abscisic acid (ABA).
Statements (i), (ii), and (iii) are correct applications of cytokinin, GA, and 2,4-D. Statement (iv) is incorrect because GAs, not ABA, hasten maturity in juvenile conifers.
Question 50 of 100
📘 CLASS XI
Evaluate the physiological outcome when specific PGR treatments or conditions occur in plants:
(i) GA3 applied to rice seedlings causes rapid stem elongation (bakanae effect). (ii) Unripe fruits mixed with a rotten fruit ripen quickly due to ethylene released from rotten fruit. (iii) Forgetting to add cytokinin to tissue culture medium prevents cell division and shoot formation. (iv) Applying ABA to rice seedlings causes bolting and rapid internode elongation.
Statements (i), (ii), and (iii) are correct outcomes based on textbook principles. Statement (iv) is incorrect because GA promotes bolting and elongation, while ABA inhibits growth.
