Q11. What is the main role of cytokinins in plant growth and development?
a) Promoting cell division
b) Inducing leaf senescence
c) Enhancing root elongation
d) Stimulating flower blooming
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Correct Answer: a) Promoting cell division
Explanation: Cytokinins are a group of plant hormones that play a crucial role in promoting cell division, or cytokinesis, in plant roots and shoots. They are involved in various aspects of plant growth and development, including stimulating shoot initiation and growth, delaying leaf aging (senescence), and working in concert with auxins to regulate cell differentiation and organ development.
Q12. Which structure in plants senses gravity to direct root growth?
a) Stomata
b) Root hairs
c) Root cap
d) Leaf mesophyll
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Correct Answer: c) Root cap
Explanation: The root cap, a structure at the tip of the plant root, plays a key role in sensing gravity, which directs the growth of roots. It contains specialized cells called statocytes, which contain statoliths – small particles that settle at the bottom of the cell in response to gravity, signaling the direction of growth.
Q13. What process allows plants to move nutrients from the soil to other parts of the plant?
a) Transpiration
b) Photosynthesis
c) Osmosis
d) Capillary action
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Correct Answer: a) Transpiration
Explanation: Transpiration, the process of water movement through a plant and its evaporation from aerial parts like leaves, stems, and flowers, plays a key role in moving nutrients from the soil to other parts of the plant. As water is absorbed by roots and then evaporates from the leaves, it creates a pull that draws water and dissolved nutrients up through the plant’s vascular system (xylem).
Q14. What type of tropism is shown by plant roots growing in response to moisture?
a) Phototropism
b) Hydrotropism
c) Geotropism
d) Thigmotropism
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Correct Answer: b) Hydrotropism
Explanation: Hydrotropism is the type of tropism exhibited when plant roots grow in response to moisture. This directional growth response ensures that the roots grow towards areas with higher moisture levels, which is crucial for the plant’s ability to access water for survival and growth.
Q15. Which hormone helps in the ripening of fruits?
a) Ethylene
b) Auxin
c) Gibberellin
d) Cytokinin
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Correct Answer: a) Ethylene
Explanation: Ethylene is a plant hormone known for its role in the ripening of fruits. It is a gaseous hormone that not only triggers the ripening process but also influences other aspects of the plant’s life cycle, such as leaf abscission and flower wilting. Ethylene’s effects on fruit include softening, changes in color, and development of flavor and aroma.
Q16. Which part of a plant is primarily responsible for detecting light direction for phototropism?
a) Roots
b) Stems
c) Leaves
d) Shoot apex
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Correct Answer: d) Shoot apex
Explanation: The shoot apex of a plant is primarily responsible for detecting the direction of light for phototropism. The cells in the shoot apex are sensitive to light and play a crucial role in the plant’s growth towards the light source. The distribution of growth hormones like auxins is influenced by light direction, which causes differential growth and bending towards the light.
Q17. In plants, what is the movement of chloroplasts in response to light called?
a) Photoperiodism
b) Phototropism
c) Chloroplast migration
d) Photokinesis
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Correct Answer: c) Chloroplast migration
Explanation: Chloroplast migration in plants is the movement of chloroplasts within plant cells in response to light. When exposed to bright light, chloroplasts move to the cell walls perpendicular to the light source to avoid damage, while in low light, they position themselves along the walls parallel to the light for maximum absorption.
Q18. What phenomenon describes the seasonal timing of biological activities such as flowering and migration in response to environmental changes?
a) Phototropism
b) Photoperiodism
c) Geotropism
d) Thigmotropism
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Correct Answer: b) Photoperiodism
Explanation: Photoperiodism describes the seasonal timing of biological activities, such as flowering in plants, in response to the length of day and night. It allows organisms to synchronize their biological activities with environmental conditions, ensuring they occur at the most advantageous time of the year.
Q19. What is the process by which plants close their stomata to prevent water loss?
a) Transpiration
b) Respiration
c) Photosynthesis
d) Stomatal closure
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Correct Answer: d) Stomatal closure
Explanation: Stomatal closure is the process by which plants close their stomata to prevent water loss. Stomata are small openings on the underside of leaves that allow gas exchange. In response to environmental stresses like drought, plants close these stomata to reduce water loss through transpiration, thus conserving water.
Q20. Which hormone in plants inhibits growth and promotes dormancy?
a) Auxin
b) Gibberellin
c) Ethylene
d) Abscisic acid
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Correct Answer: d) Abscisic acid
Explanation: Abscisic acid is a plant hormone that inhibits growth and promotes dormancy, particularly in seeds and buds. It plays a key role in responding to stress conditions like drought and salinity. Abscisic acid helps to close stomata to reduce water loss and triggers dormancy mechanisms, allowing plants to survive adverse conditions.