In monocot roots, the absence of secondary growth is primarily due to:
Answer: A
Monocots lack a functional vascular cambium, which is essential for secondary growth, hence they remain herbaceous throughout life.
Q.62Medium
The Casparian strip found in the endodermis of roots is composed primarily of:
Answer: A
The Casparian strip is an impermeable band of suberin and lignin that prevents lateral movement of water and minerals, forcing them through the endoderm symplastically.
Q.63Medium
Which anatomical feature distinguishes the anatomy of a typical dicot leaf petiole from that of a monocot?
Answer: A
Dicot petioles typically have multiple vascular bundles arranged in a ring or scattered pattern, while monocots have scattered bundles throughout.
Q.64Medium
Tracheids differ from vessel elements in that tracheids:
Answer: A
Tracheids lack perforation plates, have oblique overlapping end walls with bordered pits, and are found in both gymnosperms and angiosperms, conducting water more slowly than vessel elements.
Q.65Medium
The mestome sheath observed in some monocot leaves functions primarily to:
Answer: A
The mestome sheath, composed of sclerenchyma fibers, surrounds the vascular bundle and provides mechanical strength to the leaf structure.
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Q.66Easy
In xerophytic plants, which adaptation reduces the surface area for transpiration?
Answer: A
Xerophytes have a thick, waxy cuticle and stomata sunken in pits (crypts), which reduces direct exposure to air and decreases transpiration rate.
Q.67Medium
The phenomenon of radial vascular bundles is characteristic of:
Answer: A
Radial arrangement of xylem and phloem in alternate pattern is typical of dicot roots, where xylem arms point toward the periphery and phloem patches lie between them.
Q.68Medium
Companion cells in angiosperms are specifically associated with:
Answer: A
Companion cells are living cells derived from the same mother cell as sieve tubes; they provide metabolic support and regulate loading/unloading of photosynthates.
Q.69Easy
The prismatic crystals often found in vacuoles of plant cells serve primarily to:
Answer: A
Calcium oxalate crystals store excess calcium ions and help maintain osmotic balance in plant cells.
Q.70Medium
In hydrophytic plants, aerenchyma tissue is primarily composed of:
Answer: A
Aerenchyma consists of large air-filled intercellular spaces that facilitate gas exchange and provide buoyancy in aquatic plants.
Q.71Hard
The pericycle in roots gives rise to all EXCEPT:
Answer: C
Root hairs develop from the root hair zone of epidermis, not from pericycle. The pericycle produces lateral roots, vascular cambium, and in some species, cork cambium.
Q.72Easy
Which type of vascular bundle arrangement is characteristic of monocot stems?
Answer: A
Monocot stems have numerous scattered collateral vascular bundles distributed throughout the ground tissue, unlike the organized ring in dicots.
Q.73Medium
The anatomical basis for the superior mechanical strength of dicot stems compared to monocot stems is:
Answer: A
Dicots develop secondary tissues (secondary xylem and phloem) through vascular cambium activity, creating dense wood that provides greater mechanical strength than herbaceous monocots.
Q.74Medium
In gymnosperms, the conducting tissue in xylem is primarily composed of:
Answer: A
Gymnosperms lack vessel elements and rely on tracheids with bordered pits for water conduction, which is less efficient than angiosperm vessel elements.
Q.75Hard
The bulliform cells found in monocot leaves, particularly in grasses, function to:
Answer: A
Bulliform cells are large, colorless epidermal cells that absorb water and swell, causing the leaf to unfold; they lose water and collapse during drought, causing leaf rolling to reduce transpiration.
Q.76Hard
The transformation of protophloem into metaphloem in developing roots results in:
Answer: A
As the root grows and matures, protophloem sieve tubes collapse and are obliterated, replaced functionally by metaphloem which lies closer to the periphery.
Q.77Medium
The anatomical adaptation of sunken stomata in xerophytes is primarily effective because it:
Answer: A
Stomatal pits create a humid chamber that reduces the vapor pressure gradient between intercellular spaces and external environment, thereby minimizing transpirational water loss.
Q.78Easy
In a transverse section of a dicot leaf, which tissue is primarily responsible for light absorption and sugar production?
Answer: A
Palisade mesophyll consists of tightly packed columnar cells with numerous chloroplasts oriented toward light, maximizing photosynthetic efficiency.
Q.79Medium
The presence of sclerenchyma fibers in the phloem tissue (phloem fibers) primarily serves to:
Answer: A
Phloem fibers (bast fibers) provide mechanical support to vascular bundles and stems while permitting the translocation function of sieve tubes and companion cells.
Q.80Easy
Which of the following is a characteristic feature of secondary xylem in dicots?
Answer: A
Secondary xylem in dicots shows growth rings (annual rings) due to variations in cell size and wall thickness between spring wood and autumn wood formed in different seasons.
