Q11. Which of the following is NOT a component of the phloem tissue in plants?
a) Sieve tube elements
b) Companion cells
c) Tracheids
d) Phloem fibers
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Correct Answer: c) Tracheids
Explanation: Tracheids are part of the xylem tissue responsible for water transport and structural support. In contrast, the phloem tissue consists of sieve tube elements, companion cells, phloem fibers, and various specialized cells involved in the transport of organic compounds.
Q12. Which of the following statements best describes the role of the phloem in plants?
a) It transports water and minerals from roots to leaves.
b) It transports sugars and other organic compounds from leaves to other parts of the plant.
c) It provides structural support to the plant.
d) It is involved in gas exchange between the plant and the atmosphere.
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Correct Answer: b) It transports sugars and other organic compounds from leaves to other parts of the plant.
Explanation: The primary role of the phloem in plants is to transport sugars, amino acids, hormones, and other organic compounds synthesized in the leaves (source) to other parts of the plant, such as roots, stems, and developing fruits (sink), where they are used for growth and metabolism.
Q13. Which of the following is a mechanism by which sugars are actively loaded into the sieve tube elements of the phloem?
a) Osmosis
b) Facilitated diffusion
c) Symplastic transport
d) Active transport
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Correct Answer: d) Active transport
Explanation: Active transport is the mechanism by which sugars are actively loaded into the sieve tube elements of the phloem. This process requires energy and typically involves the use of proton pumps or ATPase pumps to create a concentration gradient that drives the movement of sugars against their concentration gradient.
Q14. What is the name of the region in the stem where sugars are actively unloaded from the phloem and utilized for growth and metabolism?
a) Source
b) Sink
c) Xylem
d) Cambium
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Correct Answer: b) Sink
Explanation: Sink regions in the plant, such as roots, developing fruits, and growing tissues, are sites where sugars and other organic compounds transported through the phloem are actively unloaded and utilized for growth, storage, and metabolism. Sink organs rely on a constant supply of assimilates from source organs.
Q15. Which of the following is a mechanism by which sugars are passively unloaded from the phloem into sink tissues?
a) Active transport
b) Facilitated diffusion
c) Symplastic transport
d) Bulk flow
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Correct Answer: b) Facilitated diffusion
Explanation: Facilitated diffusion is the mechanism by which sugars are passively unloaded from the phloem into sink tissues. In this process, sugars move down their concentration gradient through specialized transport proteins in the plasma membranes of sink cells, without requiring energy expenditure by the plant.
Q16. Which of the following substances is transported through the xylem from roots to leaves?
a) Sugars
b) Amino acids
c) Water and minerals
d) Hormones
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Correct Answer: c) Water and minerals
Explanation: The xylem is responsible for transporting water and minerals absorbed by the roots from the soil to the aerial parts of the plant, including stems, leaves, and flowers. This upward movement of water and minerals is essential for maintaining turgor pressure, supporting photosynthesis, and facilitating nutrient uptake.
Q17. What is the primary driving force for the movement of water and minerals in the xylem?
a) Active transport
b) Transpiration pull
c) Osmosis
d) Diffusion
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Correct Answer: b) Transpiration pull
Explanation: Transpiration pull, generated by the loss of water vapor from the leaves through stomata during transpiration, creates a negative pressure gradient that pulls water upward through the xylem vessels. This cohesive and adhesive force, along with root pressure, drives the movement of water and minerals in the xylem.
Q18. Which of the following structures in the root plays a role in regulating the movement of water and minerals into the xylem?
a) Epidermis
b) Cortex
c) Endodermis
d) Pericycle
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Correct Answer: c) Endodermis
Explanation: The endodermis is a specialized layer of cells in the root responsible for regulating the movement of water and minerals into the xylem. It contains the Casparian strip, an impermeable barrier that forces water and minerals to pass through the selectively permeable plasma membranes of endodermal cells before entering the xylem vessels.
Q19. Which of the following factors contributes to the cohesion of water molecules within the xylem vessels?
a) Adhesion to the vessel walls
b) Hydrogen bonding between water molecules
c) Active transport of ions
d) Pressure gradient from roots to leaves
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Correct Answer: b) Hydrogen bonding between water molecules
Explanation: Cohesion of water molecules within the xylem vessels is primarily due to hydrogen bonding between water molecules. This cohesive force, along with adhesion to the hydrophilic walls of the vessels, enables water to form a continuous column and facilitates its upward movement through the plant.
Q20. Which of the following is NOT a mechanism by which water is transported from roots to leaves in the xylem?
a) Root pressure
b) Capillary action
c) Transpiration pull
d) Active transport
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Correct Answer: d) Active transport
Explanation: Active transport is not a mechanism involved in the transport of water from roots to leaves in the xylem. Instead, water movement in the xylem is primarily driven by root pressure, capillary action, and transpiration pull, which operate passively without requiring energy expenditure by the plant.