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.82Medium
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.83Medium
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.
Q.84Medium
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.85Medium
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.
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Q.86Medium
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.87Medium
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.88Medium
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.89Medium
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.90Medium
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.91Medium
Companion cells in phloem are primarily associated with:
Answer: B
Companion cells are closely associated with sieve tube elements and help in loading and unloading of sucrose and control of sieve tube functioning.
Q.92Medium
The anatomical feature that distinguishes protoxylem from metaxylem is:
Answer: B
Protoxylem forms first during primary development with narrow vessels and is often crushed, while metaxylem forms later with wider vessels and persists.
Q.93Medium
In xerophytic plants, the cuticle is typically:
Answer: B
Xerophytes have a thick, waxy cuticle that reduces water loss through transpiration, an important adaptation to arid environments.
Q.94Medium
The pith in a dicot stem is composed of:
Answer: A
Pith consists of parenchyma cells that serve for storage and may become lignified with age; it is surrounded by the vascular cylinder.
Q.95Medium
Which of the following cells in xylem are living at maturity?
Answer: C
Xylem parenchyma cells remain alive at maturity and are involved in storage and lateral transport, unlike tracheids and vessels which are dead at maturity.
Q.96Medium
In hydrophytes, the absence of extensive xylem development is primarily because:
Answer: A
Hydrophytes living in aquatic environments have reduced xylem development as water provides mechanical support (buoyancy) to the plant body.
Q.97Medium
In a transverse section of a typical dicot root, which tissue layer is responsible for initiating lateral roots?
Answer: C
The pericycle is the outermost layer of the stele (inside endodermis) and gives rise to lateral roots and the vascular cambium during secondary growth.
Q.98Medium
The stomatal density in mesophytic plants compared to xerophytic plants is typically:
Answer: A
Mesophytes have higher stomatal density as water is readily available, while xerophytes have lower stomatal density as an adaptation to reduce water loss.
Q.99Medium
The lenticels in woody stems are primarily involved in:
Answer: C
Lenticels are porous structures in the periderm (cork) that allow gaseous exchange (respiration) to occur in woody stems where stomata are absent.
Q.100Medium
In a transverse section of a typical monocot stem, the vascular bundles are arranged in a scattered pattern throughout the ground tissue. Which of the following anatomical features best explains why monocots can tolerate continuous growth and damage to their vascular tissues better than dicots?
Answer: A
The scattered distribution of vascular bundles in monocots (polystelic arrangement) means that damage to one bundle doesn't severely compromise the entire plant's transport system, unlike the concentric arrangement in dicots where the vascular cylinder is a continuous ring. This provides functional redundancy and allows monocots like grasses to survive grazing and mechanical damage.
