Free Forms and Functions of Plants MCQs with Answers

191. Ripening of fruits can be promoted by:

• A. Gibberellic acid
• B. Indole acetic acid
• C. Flsrcen
• D. Ethylene gas

Explanation: Ethylene gas is known as the 'ripening hormone' because it initiates the ripening process in fruits. It causes changes such as increased respiration rate, conversion of starches to sugars, and softening of the fruit cell walls, making the fruit sweeter and more palatable. On the other hand, gibberellic acid focuses on growth processes like stem elongation, indole acetic acid is involved in general plant growth, and 'Flsrcen' is not a valid term in plant biology.

192. Gibberellin was isolated from:

• A. An algae
• B. A fungus
• C. A bacterium
• D. A virus

Explanation: The correct answer is that gibberellins were first isolated from a fungus, specifically Gibberella fujikuroi. This fungus is known for causing the 'foolish seedling' disease in rice, which results in excessive elongation of the plant. Algae, bacteria, and viruses do not produce gibberellins and are therefore incorrect choices for this question.

193. Auxins inhibit the growth of:

• A. Apical buds
• B. Lateral buds
• C. Parthenocarpy
• D. Root growth

Explanation: Auxins are plant hormones that play a crucial role in regulating plant growth processes. They are primarily known for promoting the growth of the apical bud while inhibiting the growth of lateral buds, a phenomenon known as apical dominance. This is why they inhibit the growth of lateral buds, as the plant directs more resources to the elongation of the main stem. In contrast, auxins promote root growth at low concentrations and can encourage parthenocarpy in some plants. Therefore, the correct answer is that auxins inhibit the growth of lateral buds.

194. A hormone that prevents senescence in leaves, is:

• A. Auxin
• B. Gibberellins
• C. Cytokinin
• D. Abscisic acid

Explanation: Leaf senescence is a degenerative process among which cellular organelles and biomolecules are broken down and resultant catabolites are mobilized to sink tissues such as reproductive organs and new leaves. Cytokinins help to maintain the plant cells and expression of cytokinin biosynthesis genes late in development prevents leaf senescence. Hence the answer is C.

195. Florigen is produced by:

• A. Flowers
• B. Flower-buds
• C. Leaves (CORRECT)
• D. Fruits

Explanation: Florigen is a plant hormone produced in the leaves. It acts as a long-distance signaling molecule that travels to the shoot apical meristem, promoting the transition from vegetative growth to flowering. This process is crucial for the plant's reproductive success. Option C is correct because leaves are where this hormone is synthesized. Options A, B, and D are incorrect as flowers, flower-buds, and fruits do not produce florigen. They play roles in the reproductive cycle of plants but are not the source of this specific hormone.

196. The phenomenon that a seed fails to germinate in spite of providing all conditions necessary for germination is _

• A. Photoperiodism
• B. Vernalization
• C. Dormancy
• D. Phytochrome

Explanation: Seeds of some plants do not germinate even under favourable conditions. This is called dormancy. It is under endogenous control.

197. Pulvinus tissues are present at:

• A. Leaf-tip
• B. Leaf-margin
• C. Leaf-base
• D. Middle-vein

Explanation: Pulvini may be present at the base or apex of the petiole, they consist of a core of vascular tissue within a flexible, bulky cylinder of thin walled parenchyma cells. Therefore the correct answer will be C.

198. The response of a plant related to the length of the day and night is called:

• A. Photo-receptor
• B. Photo-taxis
• C. Photo-tropism
• D. Photo-Periodism

Explanation: Photoperiodism is the ability of plants and animals to measure environmental day length (photoperiod), typically by monitoring night length. This process underlies a biological calendar. Photoperiod is inversely correlated to the nightly duration of melatonin secretion in animals.

199. The temperature required for vernalization is approximately:

• A. 2˚C
• B. 3˚C
• C. 4˚C
• D. 10˚C

Explanation: Vernalization requires an exposure to temperatures between 0-6 °C for several months.

200. A hormone that helps in growing seedless grapes.

• A. Auxins
• B. Cytokinins
• C. Ethylene
• D. Gibberellins

Explanation: Gibberellin is a plant hormone regulating key processes in plants; many of them are of significant agricultural importance, such as seed germination, root and shoot elongation, and flowering. Perhaps the most widespread use of gibberellin has been in grape production. The application of gibberellin is a regular practice for the culture of the 'Thompson Seedless' ('Sultanina') cultivar of grapes to increase fruit size and is also used to induce seedlessness in certain other grape varieties.