Q31. What phenomenon explains the closing of the Venus Flytrap?
a) Rapid leaf growth
b) Electrical impulses in cells
c) Phototropism
d) Water pressure changes
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Correct Answer: b) Electrical impulses in cells
Explanation: The closing of the Venus Flytrap is a result of electrical impulses in its cells. When an insect or other stimulus touches the sensitive hairs inside the trap, it triggers an electrical signal that changes the water pressure in the cells, causing the trap to snap shut rapidly. This is a form of rapid plant movement known as thigmonasty or seismonasty.
Q32. Which of the following is a primary role of plant hormones?
a) Conducting water from roots to leaves
b) Supporting plant in standing upright
c) Regulating plant growth and development
d) Transporting nutrients from leaves to other parts
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Correct Answer: c) Regulating plant growth and development
Explanation: Plant hormones play a crucial role in regulating plant growth and development. They are involved in processes such as cell division, elongation, flowering, fruit ripening, and response to stress. Different hormones, including auxins, cytokinins, gibberellins, ethylene, and abscisic acid, have specific functions in the life cycle of a plant.
Q33. What triggers the opening and closing of stomata in leaves?
a) Air humidity
b) Light intensity
c) Wind speed
d) Soil texture
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Correct Answer: b) Light intensity
Explanation: The opening and closing of stomata in leaves are primarily triggered by light intensity. In the presence of light, stomata usually open to allow for the exchange of gases (CO2 intake for photosynthesis and O2 release). They close in the dark to conserve water. Stomatal movement is also influenced by factors like water availability, air humidity, and internal plant signals.
Q34. Which type of plant hormone promotes cell division in shoots and is involved in seed germination?
a) Ethylene
b) Abscisic acid
c) Cytokinins
d) Gibberellins
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Correct Answer: d) Gibberellins
Explanation: Gibberellins are a type of plant hormone that promotes cell division in shoots and plays a vital role in seed germination, stem elongation, and fruit development. They help in breaking seed dormancy, stimulate enzyme production for food mobilization in seeds, and influence overall growth and development in plants.
Q35. What process do plants use to move against the force of gravity?
a) Phototropism
b) Hydrotropism
c) Geotropism
d) Thigmotropism
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Correct Answer: c) Geotropism
Explanation: Geotropism, also known as gravitropism, is the process plants use to grow in response to gravity. Roots typically display positive geotropism by growing downwards, while shoots exhibit negative geotropism by growing upwards. This directional growth allows roots to anchor the plant and absorb nutrients, and shoots to access sunlight for photosynthesis.
Q36. What is the main role of abscisic acid in plants?
a) Promoting flowering
b) Enhancing seed germination
c) Stimulating fruit ripening
d) Inducing stomatal closure during stress
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Correct Answer: d) Inducing stomatal closure during stress
Explanation: Abscisic acid primarily plays a role in inducing stomatal closure during stress conditions, such as drought. This hormone signals the guard cells around stomata to close, reducing water loss through transpiration. It also plays a role in seed dormancy, ensuring that seeds only germinate under favorable conditions.
Q37. In plants, what type of movement is shown by sunflowers tracking the movement of the sun?
a) Nastic movement
b) Seismonastic movement
c) Circadian movement
d) Heliotropism
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Correct Answer: d) Heliotropism
Explanation: Heliotropism, also known as solar tracking, is the movement shown by sunflowers as they track the movement of the sun across the sky. This type of movement allows the plant to maximize its exposure to sunlight for photosynthesis. In sunflowers, young flower heads exhibit this movement, but it stops once the flower begins to bloom.
Q38. Which process describes the lateral movement of nutrients and water from root hair cells to xylem vessels in plants?
a) Transpiration
b) Translocation
c) Active transport
d) Lateral transport
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Correct Answer: b) Translocation
Explanation: Translocation in plants refers to the movement of nutrients and water laterally from root hair cells to the xylem vessels. This process involves both passive and active transport mechanisms and is essential for transporting water and dissolved nutrients from the soil to the plant’s vascular system for distribution to various parts.
Q39. What are the tiny pores on the surface of plant leaves called?
a) Root hairs
b) Stomata
c) Xylem
d) Phloem
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Correct Answer: b) Stomata
Explanation: Stomata are tiny pores located on the surface of plant leaves (and some stems). They play a critical role in gas exchange, allowing carbon dioxide to enter for photosynthesis and oxygen and water vapor to exit. The opening and closing of stomata are controlled by surrounding guard cells, enabling the plant to regulate transpiration and photosynthesis efficiently.
Q40. What causes the rapid leaf movement in Mimosa pudica (the ‘touch-me-not’ plant)?
a) Changes in water pressure in leaf cells
b) Electric signals stimulating leaf movement
c) Rapid cell growth on one side of the leaf
d) A sudden release of stored energy
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Correct Answer: a) Changes in water pressure in leaf cells
Explanation: In Mimosa pudica, also known as the ‘touch-me-not’ plant, the rapid leaf movement is caused by changes in water pressure within the leaf cells. When stimulated by touch, the cells lose water rapidly, causing the leaf to fold and droop. This is a type of seismonastic movement and is thought to help protect the plant from herbivores or other disturbances.