Plant growth and development practice · Mixed difficulty

Option C (Auxin) is correct because auxin can inhibit abscission and counteract the effects of ethylene.

Option B (ABA) is correct because abscisic acid (ABA) is a plant hormone that inhibits growth and promotes dormancy, thus acting as an anti-gibberellin.

Option B (Leaf Abscission ) is correct because senescence leads to the formation of the abscission layer, causing leaf fall.

Option A is correct because the ratio of red-absorbing phytochrome (Pr) to far-red-absorbing phytochrome (Pfr) at dawn provides information about the length of the night, influencing photoperiodic responses.

Option A (Cytokinins - Used to prepare weed-free lawns) is correct because auxins, not cytokinins, are used in weed-free lawns as herbicides.

Option C (promote root growth and roothair formation to increase the absorption surface) is correct because ethylene promotes root growth and root hair formation.

Option C (I, IV) is correct because Zeatin is an adenine derivative that overcomes apical dominance, and GA3 is a terpene that induces bolting in cabbage.

The correct answer is A (13 hours light, 11 hours dark) because for a plant with a 13-hour critical day length, flowering will occur if the light period is equal to or less than the critical day length. Since the question is not specifying if the plant is a long-day or short-day plant, we assume it is a long-day plant.

Option D (If both Assertion and Reason are false) is correct because apical dominance is decreased, not increased, by removing the shoot tip, and the inhibition is due to auxin produced in the apical bud, not its accumulation in lateral parts after removal.

Option B is correct because W1 represents the final size, W0 the initial size, r the growth rate, and t the time of growth in the geometrical growth equation.

Option C (Both (1) and (2)) is correct because both natural and synthetic auxins are widely used in agriculture for purposes like weed control and in horticulture for promoting rooting and fruit development.

Option B is correct because Short Day Plants (SDP) require a long period of darkness (long night) to initiate flowering.

Option D (Both (a) and (b)) is correct because sleep movements in plants are nastic responses triggered by daily changes in both light and darkness.

Option A (Cell elongation) is correct because auxin primarily promotes cell elongation, especially in stems and roots.

Option D (All of these) is correct because primary growth in plants is contributed by root apical meristem, shoot apical meristem, and intercalary meristem.

The correct answer is D (Both (A) and (R) are false) because flowering in plants depends on a combination of light and dark exposure AND the relative duration of light and dark hours is crucial for many plants (short-day and long-day plants).

Option D (I and II) is correct because cytokinins delay senescence and auxins regulate apical dominance.

The correct answer is D (Delay senescence by GA) because Gibberellins (GA) can delay senescence in fruits, allowing them to be left on the tree longer and increase the market period.

Option C (Outward movement of protons) is correct because the proton pump uses ATP to actively transport protons out of the guard cells, creating an electrochemical gradient that drives potassium uptake.

Option A (I, IV only) is correct because growth and differentiation in higher plants are open, and a defoliated plant cannot respond to the photoperiodic cycle.

Option B (Amino purines) is correct because cytokinins are primarily adenine derivatives, which are amino purines, playing a crucial role in cell division and differentiation.

Option D (IAA) is correct because Indole-3-acetic acid (IAA) is the most common naturally occurring auxin in plants.

Option C (Senescence tissues and ripening fruits) is correct because ethylene production is highest in senescing tissues and ripening fruits.

The correct answer is C (Induce dormancy) because gibberellins typically break dormancy, while inducing dormancy is a function of abscisic acid (ABA).

Option A (Growth regulators) is correct because growth regulators are intrinsic factors influencing plant development.

The correct answer is D (Both (a) and (c)) because vernalization shortens both the reproductive and vegetative phases by inducing early flowering.

Option B (Controls xylem differentiation) is correct because Cytokinins, initially discovered as promoting cell division, also play a role in xylem differentiation.

Option B (2) is correct because ethylene's promotion of seed/bud dormancy breaking and germination initiation are antagonistic to abscisic acid's (ABA) role in promoting dormancy.

Option B (Altering the plasticity of cell walls) is correct because auxin increases cell wall plasticity, allowing for cell expansion and growth.

Option A (Limnophila heterophylla) is correct because it is a well-known example of a plant exhibiting adaptive heterophylly.