Free Forms and Functions of Plants MCQs with Answers

51. 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.

52. 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.

53. 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.

54. 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.

55. 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.

56. All of the following are methods to break the seed dormancy EXCEPT

• A. Exposing the seeds to heat
• B. Treating the seed coats with acid
• C. Keeping the seed coats hard and dry
• D. Giving low temperature treatment to seeds

Explanation: The only option that does not break dormancy is keeping the seed coats hard and dry, hence option C is correct.To break seed dormancy, methods like exposing seeds to heat, treating seed coats with acid, and giving seeds low-temperature treatment are effective. Heat softens hard seed coats, acid mimics digestive processes that weaken the coat, and cold stratification triggers biochemical changes in seeds with physiological dormancy. In contrast, keeping seed coats hard and dry does not break dormancy.

57. Biennials and perennial plants are stimulated to produce flowers by exposing them to low temperature. In these plants, the low temperature stimulus is received by the I. Shoot apex of a mature stem II. Embryo of the seed III. Leaves

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

Explanation: Only option I and II are correct as In many biennials (e.g., carrot, beet) and some perennials, the shoot apical meristem is the site where vernalization occurs.The shoot apex contains meristematic tissue, which can respond to cold and later initiate flowering when conditions become favorableIn some plants, especially winter annuals and cereals like wheat, barley, and rye, the embryo inside the seed perceives the cold treatment.(option I)Seeds are exposed to low temperatures (called stratification) to break dormancy and promote flowering after germinationLeaves are not the primary site for vernalization.(option II)Although leaves can sense photoperiod (day length) through phytochrome, they cannot perceive cold stimulus for vernalization.The cold must act on meristematic tissues, not on mature leaf cells, which lack the ability to initiate flowering signals in response to cold.(option III)

58. The experimental set-up that is used MAINLY to demonstrate positive geotropism in plants is

• A. A
• B. B
• C. C
• D. D

Explanation: Only option B shows positive geotropism as pea seedling growing in a porous pot and sand, with roots growing downwards demonstrates Positive Geotropism. The image clearly shows the roots of the pea seedling growing vertically downwards, following the pull of gravity, which is the definition of positive geotropism. The setup ensures the plant is growing in a condition where the root's response to gravity can be easily observed.

59. A farmer wants to ripen the raw apples in his farm. For this purpose, he keeps the raw apples with the apples that are already ripened.The hormone produced by the ripened apples is

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

Explanation: The correct answer is Option B, also known as ethylene, is a plant hormone that is crucial in the ripening of fruits. It acts by breaking down cell walls, converting starches to sugars, and decreasing acidity, which collectively contribute to the ripening process. While auxins, cytokinins, and gibberellins have their roles in plant growth and development, they are not directly responsible for the fruit ripening process. Auxins primarily aid in cell elongation, cytokinins in cell division, and gibberellins in growth, but ethene is the key hormone for ripening.

60. During seed dormancy, seeds do not germinate because the seeds

• A. Are devoid of all kinds of nutrients
• B. Could produce fruits with hard fruit wall
• C. Require a period of rest before germination
• D. Could produce plants that are vulnerable to diseases

Explanation: The correct answer is that seeds require a period of rest before germination (Option C). Seed dormancy is a survival strategy to prevent germination during unfavorable conditions. This allows seeds to remain viable until environmental conditions are optimal for growth. Option A is incorrect because seeds contain nutrients necessary for early growth. Option B is irrelevant as the fruit wall's hardness doesn't affect seed dormancy. Option D is incorrect because dormancy is unrelated to disease vulnerability.