Free Plant Growth Regulators MCQs with Answers

1. The hormone(s) synthesised in the meristematic tissue of the plant shoot and root is/ areI. Abscisic acidII. AuxinIII. Cytokinin

• A. I only
• B. II only
• C. I and II
• D. II and III

Explanation: The correct answer is D. II and III. Both auxin and cytokinin are hormones synthesized in meristematic tissues of plants. Auxin is primarily responsible for cell elongation and is synthesized at the tips of shoots and roots. Cytokinin promotes cell division and differentiation and is also synthesized in these meristematic areas. Abscisic acid, on the other hand, is mainly involved in stress responses and is not typically synthesized in meristematic tissues, making options A, B, and C incorrect.

2. The given diagram shows a stem tendril helping a plant to climb up a support.The type of growth movement exhibited by the plant is

• A. Epinasty
• B. Nutation
• C. Hyponasty
• D. Nyctinasty

Explanation: Nutation is a type of growth movement where a plant part, such as a stem or tendril, exhibits revolving or spiraling motion. The tip of a climbing plant's stem or tendril may sway back and forth (nutation) as it searches for a support. So option B is correct. All other processes are not related to the climbing movement shown.

3. Auxins and gibberellins are plant hormones. The common role of these hormones is to

• A. Delay both bud initiation and leaf senescence
• B. Promote both bud initiation and leaf senescence
• C. Promote bud initiation and delay leaf senescence
• D. Promote leaf senescence and delay bud initiation

Explanation: The correct answer is that auxins and gibberellins promote bud initiation and delay leaf senescence. These plant hormones are involved in various growth processes, including the stimulation of bud growth. They help maintain the plant's vitality by delaying the aging of leaves, which is a process known as leaf senescence. The incorrect options either misstate the effects of these hormones on buds and leaves or reverse their roles entirely.

4. The given diagrams, I and II, show the growth of a plant without and with hormone treatment. Based on the shown effect in diagram II, the hormones used in the mixture must be

• A. Ethene and Auxin
• B. Auxin and Gibberellin
• C. Abscisic acid and Ethene
• D. Gibberellin and Abscisic acid

Explanation: The correct answer is Option B: auxin and gibberellin. These two hormones are known to promote plant growth by stimulating cell elongation and division. In the context of the diagrams, this combination would result in enhanced growth as shown in diagram II. Other options are incorrect because they include hormones like abscisic acid, which inhibits growth, or ethene, which primarily affects fruit ripening and leaf abscission rather than growth promotion.

5. Consider the given diagram. The phenomenon which induces the growth of plant I is

• A. Vernalization
• B. Seed dormancy
• C. Photoperiodism
• D. Seed germination

Explanation: The correct answer is Vernalization . Vernalization is a process in which the prolonged exposure to cold temperatures triggers the flowering of plants. This is essential for certain plants to transition from vegetative growth to flowering. The other options are related to plant growth but do not specifically describe the cold-induced flowering process:Seed dormancy refers to a period when seeds are inactive and not germinating, which is unrelated to the specific growth induction described.Photoperiodism involves the plant's response to the duration of light and dark periods, primarily affecting flowering time rather than the initial growth process.Seed germination is the process of a seed starting to grow, which is a different stage of development and not induced by cold exposure as vernalization is.

6. The option that identifies the plant's response provoked by red and blue light is

• A. Red light enhances cell division, blue light promotes cell elongation
• B. Red light promotes cell elongation, blue light enhances cell division
• C. Red light enhances cell division, blue light retards cell enlargement
• D. Red light promotes cell elongation, blue light retards cell division

Explanation: The correct answer is that red light enhances cell division, and blue light promotes cell elongation. Red light is crucial for processes like flowering and seed germination, which involve cell division. Blue light, on the other hand, is essential for phototropism and can increase the rate of cell elongation, which is important for the growth direction of plants. The other options confuse these roles or represent rare or incorrect generalizations about plant responses to light.

7. The given diagram shows the histology of a developing shoot of a plant.The labelled structure gives rise to

• A. Bark
• B. Leaves
• C. Lateral shoots
• D. Vascular cambium

Explanation: Leaf Primordia: These are young leaf tissues that form on the flanks of the SAM and will develop into mature leaves. So option B is correct. Leaf primordia do not give rise to bark, lateral shoots and vascular cambium. So A,C and D are incorrect.

8. Roots exhibit negative phototropism.To demonstrate the reason of this phenomenon, the roots of a potted plant are placed parallel tothe soil. The result shows that auxin gathers in the

• A. lower half of the root and stimulates growth.
• B. lower half of the root and slows down the growth.
• C. upper half of the root and slows down the growth.
• D. Upper half of the root and stimulates growth

Explanation: In a root placed horizontally, the bottom side contains more auxin and grows less, causing the root to move away from light. So option B is correct. All other options are incorrect.

9. The hormone used commercially to delay the process of ripening and to improve the storagelife of bananas and grapefruits is

• A. Auxin
• B. Gibberellin
• C. Cytokinin
• D. Ethene

Explanation: Gibberellin is the correct answer because it is a plant hormone that plays a critical role in the ripening process of fruits. In commercial settings, controlling gibrellin levels can delay ripening, allowing fruits like bananas and grapefruits to have an extended storage life. The other options, such as auxin, cytokinin, and ethene, have different primary functions related to plant growth and development, but they are not specifically used for controlling fruit ripening in storage.

10. Long-day plants normally do not flower during the winters.Horticulturalists can trigger the process of flowering in a long-day plant during winters by

• A. Keeping the plant warm during the night-time
• B. Exposing the plant to a light source during the night
• C. Covering the plant with a black cloth for 12 hours a day
• D. Covering the plant with a transparent plastic during the daytime

Explanation: Long-day plants require a certain length of daylight to trigger flowering. By artificially extending the day length with additional light exposure during the night, horticulturalists can induce flowering in these plants even during the shorter days of winter. Option B is correct because it involves increasing the exposure to light, simulating longer days. Option A is incorrect as warmth does not directly affect photoperiodism. Option C is incorrect because reducing the light period with a black cloth simulates shorter days, which is unsuitable for long-day plants. Option D is incorrect as covering with transparent plastic does not alter the light exposure significantly.