Q21. What type of movement in plants involves a reversible change in shape but no growth?
a) Tropism
b) Nastic movement
c) Growth-dependent movement
d) Photoperiodism
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Correct Answer: b) Nastic movement
Explanation: Nastic movements in plants involve reversible changes in shape or position that are not directed by the stimulus source and do not involve growth. These movements are often triggered by environmental factors such as light, temperature, and touch, but the direction of movement is independent of the stimulus’s direction. Examples include the closing of flower petals at night and the rapid folding of Mimosa pudica leaves upon touch.
Q22. How do climbing plants, like vines, adhere to surfaces?
a) By rootlets
b) By twining stems
c) By leaf tendrils
d) Both a) and c)
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Correct Answer: d) Both a) and c)
Explanation: Climbing plants, like vines, can adhere to surfaces in several ways. Some, like English ivy, use small rootlets that grow out of the stem and adhere to surfaces. Others, like grapevines, use tendrils which are specialized structures that coil around supports. Some climbers, like pole beans, have twining stems that wrap around supports.
Q23. What is the primary function of guard cells in plants?
a) To carry out photosynthesis
b) To protect against herbivores
c) To regulate the opening and closing of stomata
d) To absorb nutrients from the soil
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Correct Answer: c) To regulate the opening and closing of stomata
Explanation: Guard cells are specialized cells in the epidermis of leaves, stems, and other organs that are responsible for regulating the opening and closing of stomata. Stomata are small openings that control gas exchange and transpiration in plants. Guard cells change shape due to turgor pressure, opening or closing the stomatal pore to regulate water loss and CO2 intake.
Q24. What causes the venus flytrap to close when an insect touches it?
a) Chemical signals from the insect
b) A rapid growth response
c) Electrical signals in the plant
d) A change in internal water pressure
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Correct Answer: c) Electrical signals in the plant
Explanation: The closing mechanism of the Venus flytrap involves electrical signals within the plant. When an insect touches the sensitive hairs on the plant’s surface, it triggers an electrical signal that causes the trap to close rapidly. This action is not a growth movement but a rapid response to the stimulus.
Q25. Which part of a plant typically shows positive geotropism?
a) Leaves
b) Flowers
c) Stems
d) Roots
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Correct Answer: d) Roots
Explanation: Roots typically show positive geotropism, meaning they grow in the direction of gravitational pull. This growth pattern ensures that roots penetrate the soil to anchor the plant firmly and access water and nutrients. In contrast, stems usually exhibit negative geotropism, growing upwards away from the earth’s gravitational pull.
Q26. What term describes the movement of a plant part in response to contact with a solid object?
a) Phototropism
b) Geotropism
c) Thigmotropism
d) Hydrotropism
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Correct Answer: c) Thigmotropism
Explanation: Thigmotropism is the movement or growth of a plant in response to touch or physical contact with a solid object. This type of movement is often seen in climbing plants like vines and creepers, where tendrils or other plant parts wrap around or cling to objects for support and stability.
Q27. Which hormone is responsible for stimulating the ripening process in fruits?
a) Ethylene
b) Auxin
c) Gibberellin
d) Cytokinin
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Correct Answer: a) Ethylene
Explanation: Ethylene, a gaseous plant hormone, is responsible for stimulating the ripening process in fruits. It promotes changes like softening, sweetening, and color development in fruits. Ethylene is not only involved in fruit ripening but also in other aspects of plant growth and development, such as leaf abscission and flower wilting.
Q28. What kind of growth movement in plants is independent of the direction of the stimulus?
a) Tropic movement
b) Nastic movement
c) Directional growth
d) Oriented movement
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Correct Answer: b) Nastic movement
Explanation: Nastic movements in plants are types of growth movements that are independent of the direction of the stimulus. These movements are triggered by environmental stimuli such as temperature, light, touch, and chemicals, but the direction of the response is not related to the direction of the stimulus. Examples include the closing of the Mimosa pudica (sensitive plant) leaves when touched and the opening and closing of flower petals in response to light and temperature changes.
Q29. Which cells in the plant are primarily responsible for elongation at the tip of a growing shoot?
a) Meristematic cells
b) Parenchyma cells
c) Guard cells
d) Xylem cells
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Correct Answer: a) Meristematic cells
Explanation: Meristematic cells are primarily responsible for the elongation at the tip of a growing shoot. These cells are located in the apical meristem at the shoot tip and are undifferentiated, actively dividing cells. They give rise to various tissues and organs of the plant and are responsible for primary growth, contributing to the lengthening of shoots and roots.
Q30. In plants, which structure is responsible for primary absorption of water and nutrients from the soil?
a) Root hairs
b) Stem tubers
c) Leaf stomata
d) Flower petals
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Correct Answer: a) Root hairs
Explanation: Root hairs, which are extensions of root epidermal cells, are responsible for the primary absorption of water and nutrients from the soil. They greatly increase the surface area of the root, enhancing its ability to absorb water and dissolved nutrients efficiently. Root hairs are in close contact with the soil particles, facilitating the uptake of essential elements required for plant growth.