Q1. What is the term used to describe the growth of a plant towards light?
a) Geotropism
b) Hydrotropism
c) Phototropism
d) Thigmotropism
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Correct Answer: c) Phototropism
Explanation: Phototropism is the growth of a plant in response to a light stimulus. Plants exhibit phototropism by growing towards a light source, which is crucial for maximizing light capture for photosynthesis. This movement towards light is mainly driven by the differential elongation of cells in the plant stem, regulated by plant hormones like auxins.
Q2. Which hormone is primarily responsible for the elongation of plant cells?
a) Gibberellin
b) Ethylene
c) Cytokinin
d) Abscisic acid
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Correct Answer: a) Gibberellin
Explanation: Gibberellins are a group of plant hormones that play a key role in the elongation of plant cells. They stimulate both cell division and elongation, which contribute to the overall growth of the plant. Gibberellins are particularly important in the rapid growth of stems and are also involved in other processes such as seed germination and flowering.
Q3. What is the movement of plants in response to touch called?
a) Phototropism
b) Thigmotropism
c) Geotropism
d) Hydrotropism
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Correct Answer: b) Thigmotropism
Explanation: Thigmotropism is the movement of plants in response to touch or physical contact. This response is observed in climbing plants like ivy and in tendrils of plants like peas, which curl around objects they touch for support. Thigmotropism helps these plants to anchor themselves and grow towards suitable structures.
Q4. Which part of the plant is responsible for absorbing water and minerals from the soil?
a) Leaves
b) Stems
c) Roots
d) Flowers
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Correct Answer: c) Roots
Explanation: The roots of a plant are responsible for absorbing water and minerals from the soil. They have a large surface area and are often covered with tiny root hairs that increase their absorptive capacity. Roots not only anchor the plant in the soil but also play a critical role in the uptake of essential nutrients and water required for plant growth and development.
Q5. What process allows plants to conserve water by opening and closing their stomata?
a) Photosynthesis
b) Transpiration
c) Respiration
d) Osmoregulation
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Correct Answer: b) Transpiration
Explanation: Transpiration is the process that allows plants to conserve water by opening and closing their stomata, which are small openings on the underside of leaves. By regulating the opening and closing of stomata, plants can control water loss through transpiration. This process is vital for maintaining water balance within the plant and is also linked to the transport of water and nutrients from the roots to the leaves.
Q6. What term describes the growth of a plant in response to water?
a) Phototropism
b) Geotropism
c) Thigmotropism
d) Hydrotropism
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Correct Answer: d) Hydrotropism
Explanation: Hydrotropism is the term used to describe the growth or movement of a plant in response to water. This type of tropism is seen when plant roots grow towards a moisture source. It is an important mechanism that allows plants to locate water in their environment, which is essential for their growth and survival.
Q7. Which hormone is known as the ‘stress hormone’ in plants?
a) Ethylene
b) Auxin
c) Abscisic acid
d) Gibberellin
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Correct Answer: c) Abscisic acid
Explanation: Abscisic acid is often referred to as the ‘stress hormone’ in plants. It plays a vital role in responding to environmental stress conditions such as drought and salt stress. Abscisic acid helps the plant conserve water by triggering the closure of stomata (thereby reducing transpiration) and by promoting root growth to access deeper water sources.
Q8. What is the role of auxin in plant growth?
a) Promoting fruit ripening
b) Enhancing seed germination
c) Stimulating root growth
d) Inhibiting leaf abscission
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Correct Answer: c) Stimulating root growth
Explanation: Auxin, a key plant hormone, plays a crucial role in stimulating root growth. It is involved in cell elongation and differentiation, which are important for root development. Auxin is also significant in other aspects of plant growth and development, including apical dominance, tropic responses (like phototropism), and vascular differentiation.
Q9. What mechanism do plants use to turn towards the light source?
a) Cellular expansion on the side facing away from the light
b) Cellular contraction on the side facing the light
c) Increasing chlorophyll concentration on the side facing the light
d) Decreasing stem length on the side facing the light
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Correct Answer: a) Cellular expansion on the side facing away from the light
Explanation: Plants turn towards the light source through cellular expansion on the side of the stem that is away from the light. This differential growth is largely driven by the distribution of auxins, which accumulate more on the shaded side, causing those cells to grow faster and the plant to bend towards the light.
Q10. What is geotropism in plants?
a) Growth in response to touch
b) Growth in response to light
c) Growth in response to gravity
d) Growth in response to chemical stimuli
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Correct Answer: c) Growth in response to gravity
Explanation: Geotropism, also known as gravitropism, is the growth of a plant in response to gravity. Roots typically exhibit positive geotropism, growing downwards, while shoots usually display negative geotropism, growing upwards. This orientation allows roots to anchor the plant and access water and nutrients from the soil, and shoots to reach towards the light.