Q21. Which of the following is responsible for the flow of water through the xylem from roots to leaves against gravity?
a) Root pressure
b) Capillary action
c) Transpiration pull
d) Active transport
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Correct Answer: c) Transpiration pull
Explanation: Transpiration pull is the primary mechanism responsible for the flow of water through the xylem from roots to leaves against gravity. It is generated by the loss of water vapor from the leaves during transpiration, creating a negative pressure gradient that pulls water upward through the xylem vessels.
Q22. What is the role of root pressure in the movement of water in the xylem?
a) It generates a positive pressure gradient that pushes water upward.
b) It facilitates the active transport of minerals into the xylem vessels.
c) It prevents the loss of water through the stomata.
d) It creates a negative pressure gradient that pulls water upward.
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Correct Answer: a) It generates a positive pressure gradient that pushes water upward.
Explanation: Root pressure is a mechanism by which water is pushed upward through the xylem from roots to stems. It occurs due to active pumping of minerals into the xylem by root cells, creating a positive pressure gradient that drives water upward. Root pressure is particularly important for water uptake in young plants and during periods of high soil moisture.
Q23. Which of the following cells in the phloem tissue lack nuclei and other organelles, allowing for efficient transport of sap?
a) Sieve tube elements
b) Companion cells
c) Tracheids
d) Parenchyma cells
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Correct Answer: a) Sieve tube elements
Explanation: Sieve tube elements are specialized cells in the phloem tissue responsible for transporting sap containing sugars and other organic compounds. They lack nuclei and other organelles, allowing for uninterrupted flow of sap through their elongated tubes. Companion cells, located adjacent to sieve tube elements, provide metabolic support to maintain sieve tube function.
Q24. What is the primary driving force for the movement of sugars and other organic compounds in the phloem?
a) Transpiration pull
b) Osmosis
c) Active transport
d) Bulk flow
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Correct Answer: d) Bulk flow
Explanation: Bulk flow is the primary driving force for the movement of sugars and other organic compounds in the phloem. It involves the mass movement of sap from source to sink tissues driven by differences in hydrostatic pressure (pressure gradient) established by active loading and unloading of solutes.
Q25. Which of the following statements best describes the function of the companion cells in the phloem?
a) They transport sugars through the phloem.
b) They provide structural support to the plant.
c) They maintain sieve tube function and support metabolic processes.
d) They regulate gas exchange between the plant and the atmosphere.
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Correct Answer: c) They maintain sieve tube function and support metabolic processes.
Explanation: Companion cells in the phloem play a crucial role in maintaining sieve tube function and supporting metabolic processes. They provide metabolic support to sieve tube elements, including loading and unloading of sugars, ATP production, and maintenance of membrane potential, ensuring efficient long-distance transport of sap.
Q26. What is the name of the tissue responsible for the lateral transport of water and nutrients within the plant?
a) Xylem
b) Phloem
c) Cambium
d) Epidermis
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Correct Answer: c) Cambium
Explanation: Cambium is a meristematic tissue located between the xylem and phloem in vascular plants. It is responsible for secondary growth and the formation of secondary xylem (wood) and secondary phloem. Cambium cells undergo cell division, producing new xylem cells toward the inside and new phloem cells toward the outside, facilitating lateral transport of water and nutrients.
Q27. Which of the following is responsible for the formation of new xylem and phloem cells during secondary growth in plants?
a) Apical meristem
b) Lateral meristem
c) Vascular cambium
d) Cork cambium
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Correct Answer: c) Vascular cambium
Explanation: Vascular cambium is a type of lateral meristem responsible for the formation of secondary xylem (wood) and secondary phloem in vascular plants during secondary growth. It undergoes cell division, producing new xylem cells toward the center (inward) and new phloem cells toward the periphery (outward), contributing to the radial growth of stems and roots.
Q28. Which of the following cells in the xylem tissue is responsible for providing structural support and storage of starch and other substances?
a) Tracheids
b) Vessel elements
c) Parenchyma cells
d) Companion cells
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Correct Answer: c) Parenchyma cells
Explanation: Parenchyma cells in the xylem tissue are responsible for providing structural support and storage of starch, oils, and other substances. They are living cells with thin primary walls and play a role in lateral transport of water and nutrients within the plant, as well as in wound healing and defense.
Q29. What is the function of the endodermis in the plant root?
a) It regulates the movement of water and minerals into the xylem.
b) It provides structural support to the root.
c) It synthesizes organic compounds for the plant.
d) It facilitates gas exchange between the root and the soil.
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Correct Answer: a) It regulates the movement of water and minerals into the xylem.
Explanation: The endodermis is a specialized layer of cells in the plant 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.
Q30. Which of the following is a key feature of the Casparian strip in the endodermis of plant roots?
a) It enhances the absorption of water and minerals.
b) It prevents the loss of water through the stomata.
c) It allows for the exchange of gases between the root and the soil.
d) It acts as a barrier to the passive flow of water and minerals into the xylem.
Show Answer
Correct Answer: d) It acts as a barrier to the passive flow of water and minerals into the xylem.
Explanation: The Casparian strip is a band of impermeable lignin and suberin found in the endodermis of plant roots. Its primary function is to act as a barrier that forces water and minerals to pass through the selectively permeable plasma membranes of endodermal cells before entering the xylem vessels, regulating their movement. This prevents the passive flow of water and minerals into the xylem and ensures selective uptake by the plant.