In a monocotyledonous stem, what specialized tissue surrounds each scattered vascular bundle, acting as a protective sheath?
Explanation: In a monocot stem, each scattered vascular bundle is surrounded by a sclerenchymatous bundle sheath. This provides essential mechanical rigidity to the scattered conducting strands.
Question 72 of 115
📘 CLASS XI
In the root endodermis, suberin deposition is not restricted to a single cell wall. On which specific walls of the endodermal cells is this waxy Casparian strip deposited?
Explanation: The waxy, water-impermeable material suberin is deposited on both the tangential and radial walls of the barrel-shaped endodermal cells. This continuous band forms the Casparian strip, which prevents water from bypassing the protoplasts.
Question 73 of 115
📘 CLASS XI
If you examine the spatial layout of scattered vascular bundles in a monocotyledonous stem, what size gradient do you observe between the center and the periphery?
Explanation: In monocotyledonous stems, the vascular bundles are scattered, but they show a distinct size gradient: the peripheral vascular bundles are generally smaller than the centrally located ones.
Question 74 of 115
📘 CLASS XI
In a dorsiventral (dicotyledonous) leaf, how are the palisade and spongy parenchyma cells oriented relative to the leaf surfaces?
Explanation: In a dorsiventral leaf, the adaxially placed palisade parenchyma is situated on the upper side, while the spongy parenchyma is situated below the palisade cells and extends down to the lower (abaxial) epidermis.
Question 75 of 115
📘 CLASS XI
A botany student identifies a plant organ as having conjoint, closed vascular bundles scattered in a parenchymatous ground tissue with an absence of phloem parenchyma. Can this plant undergo secondary growth?
Explanation: The described anatomical features (scattered conjoint closed bundles, parenchymatous ground tissue, absence of phloem parenchyma) are diagnostic of a monocotyledonous stem. Because monocotyledons have no cambium present in their vascular bundles (closed), they do not form secondary tissues and do not undergo secondary growth.
Question 76 of 115
📘 CLASS XI
If a plant cell biologist successfully removes the large central vacuoles of the epidermal cells in a young dicot stem while leaving other cellular structures intact, how would the physical layer of the epidermis be altered?
Explanation: NCERT states that epidermal cells are parenchymatous with a small amount of cytoplasm lining the cell wall and a large vacuole. The large central vacuole is physically responsible for pushing the cytoplasm to the periphery and maintaining turgor pressure against the cell wall. Without these vacuoles, the cytoplasm would collapse inward, and the cells would lose their turgidity, compromising their ability to form a compactly arranged, continuous protective layer.
Question 77 of 115
📘 CLASS XI
Why is the presence of multicellular trichomes on a desert shrub's stem considered a highly effective evolutionary adaptation to reduce water loss under extreme solar radiation?
Explanation: On the stem, the multicellular epidermal hairs are called trichomes. In arid, high-radiation environments, these structures (which can be branched/unbranched and soft/stiff) form a physical barrier over the epidermis. This boundary layer reduces air movement directly over the stomata and shades the stem, which helps in preventing water loss due to transpiration.
Question 78 of 115
📘 CLASS XI
If a chemical agent selectively blocks the cell wall thickening at the corners of collenchymatous cells in a young stem, what would be the mechanical and physiological fate of the hypodermis?
Explanation: In a young dicot stem, the outer cortical sub-zone is the hypodermis, which consists of collenchymatous cells. Collenchyma provides mechanical strength to the young stem due to localized cell wall thickenings. If corner thickening is blocked, these cells cannot provide the necessary tensile strength, and the young stem will bend and break easily under wind or physical strain.
Question 79 of 115
📘 CLASS XI
If you analyze a mature zone of a primary root and a primary stem, why do you find radial vascular bundles in the root but conjoint vascular bundles in the stem?
Explanation: In roots, xylem and phloem within a vascular bundle are arranged in an alternate manner along different radii (radial arrangement) to facilitate the efficient radial absorption and translocation of water and minerals from the cortex into the central stele. In stems, conjoint vascular bundles have xylem and phloem jointly situated along the same radius. This arrangement aligns with the vertical conducting pathways of the shoot axis to support leaves and branches.
Question 80 of 115
📘 CLASS XI
A plant pathologist observes a transverse section of an unknown herbaceous stem. The section shows a single-layered endodermis containing high concentrations of starch grains, but no suberized Casparian strips. What is this specimen?
Explanation: In a young dicotyledonous stem, the innermost layer of the cortex is the endodermis. The cells of this endodermis are rich in starch grains, which is why it is referred to as the starch sheath. Unlike the root endodermis, which contains water-impermeable suberin in the form of Casparian strips, the dicot stem endodermis serves as a specialized starch storage layer.
