Q41. Which of the following structures in the plant stem is responsible for providing protection against water loss, mechanical damage, and pathogens?
a) Xylem
b) Phloem
c) Epidermis
d) Cortex
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Correct Answer: c) Epidermis
Explanation: The epidermis is the outermost layer of cells in the plant stem responsible for providing protection against water loss, mechanical damage, and pathogens. It serves as a barrier to external threats and contains specialized structures such as stomata and trichomes that regulate gas exchange and reduce water loss.
Q42. What is the primary role of trichomes in the epidermis of plant stems and leaves?
a) Gas exchange
b) Water absorption
c) Protection against herbivores and pathogens
d) Photosynthesis
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Correct Answer: c) Protection against herbivores and pathogens
Explanation: Trichomes are hair-like structures found on the surface of plant stems and leaves, primarily in the epidermis. Their primary role is to provide protection against herbivores and pathogens by physically impeding access, secreting toxic or repellent substances, and reducing water loss through transpiration.
Q43. Which of the following structures in the plant stem is responsible for secondary growth and the formation of wood?
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 wood (secondary xylem). Cambium cells undergo cell division, producing new xylem cells toward the inside and new phloem cells toward the outside, contributing to the radial growth of stems and roots.
Q44. What is the function of the pith in plant stems?
a) Storage of starch and other substances
b) Transportation of water and minerals
c) Formation of lateral roots
d) Facilitation of gas exchange
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Correct Answer: a) Storage of starch and other substances
Explanation: The pith is a central region of parenchyma cells located in the center of certain plant stems. Its primary function is the storage of starch, water, and other substances. The pith provides mechanical support to the stem and may also play a role in nutrient storage and metabolism.
Q45. Which of the following statements best describes the function of the vascular bundles in plant stems?
a) They provide structural support to the stem.
b) They transport water and minerals from roots to leaves.
c) They transport sugars and other organic compounds from leaves to other parts of the plant.
d) They facilitate gas exchange between the stem and the atmosphere.
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Correct Answer: b) They transport water and minerals from roots to leaves.
Explanation: Vascular bundles are clusters of xylem and phloem tissues responsible for the transport of water and minerals from roots to leaves and the transport of sugars and other organic compounds from leaves to other parts of the plant. They provide structural support to the stem and are distributed throughout the stem in various arrangements depending on the plant species.
Q46. What is the primary function of the endodermis in plant roots?
a) Transportation of water and minerals
b) Storage of starch and other substances
c) Formation of lateral roots
d) Regulation of water and mineral uptake
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Correct Answer: d) Regulation of water and mineral uptake
Explanation: The endodermis is a specialized layer of cells in plant roots responsible for regulating the movement of water and minerals into the vascular tissues. 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, regulating their uptake.
Q47. Which of the following is responsible for the formation of secondary phloem in plants?
a) Vascular cambium
b) Cork cambium
c) Apical meristem
d) Pericycle
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Correct Answer: a) Vascular cambium
Explanation: Vascular cambium is a lateral meristem responsible for the formation of secondary phloem in plants during secondary growth. It undergoes cell division, producing new phloem cells toward the outside and new xylem cells toward the inside, contributing to the radial growth of stems and roots and the production of woody tissues.
Q48. What is the primary function of the cork cambium in plants?
a) Formation of secondary xylem
b) Formation of secondary phloem
c) Formation of cork cells for protection
d) Transportation of water and nutrients
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Correct Answer: c) Formation of cork cells for protection
Explanation: Cork cambium, also known as phellogen, is a lateral meristem responsible for the formation of cork cells in the outer bark of woody stems and roots. Cork cells provide protection against water loss, mechanical damage, and pathogens, and they contribute to the formation of bark in older woody plants.
Q49. Which of the following is responsible for the transport of sugars and other organic compounds in the phloem?
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 the transport of sugars, amino acids, hormones, and other organic compounds in the form of sap. They lack nuclei and other organelles to allow for efficient sap flow and are interconnected to form sieve tubes that transport assimilates throughout the plant.
Q50. What is the primary driving force for the movement of sap 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 sap in the phloem. It involves the mass movement of sugars and other organic compounds from source to sink tissues driven by a pressure gradient established by active loading and unloading of solutes. Bulk flow allows for rapid and efficient long-distance transport in the phloem.