The endodermis in roots is primarily characterized by the presence of:
Answer: A
Casparian strips are band-like thickening of suberin and lignin on radial and transverse walls of endodermis that regulate water and mineral movement into the stele.
Q.82Easy
In a monocot stem, the vascular bundles are typically:
Answer: A
Monocot stems have scattered vascular bundles distributed throughout the ground tissue (atactostele), unlike dicots where they form a ring.
Q.83Easy
Which tissue is responsible for the continuous growth in diameter of dicot stems?
Answer: B
Vascular cambium produces secondary xylem inward and secondary phloem outward, causing increase in diameter (secondary growth) of dicot stems.
Q.84Easy
The tissue that replaces epidermis in older roots and stems of woody plants is:
Answer: A
Periderm (cork) is produced by cork cambium and replaces the epidermis in older roots and stems, providing protection.
Q.85Medium
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.
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Q.86Medium
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.87Medium
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.88Medium
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.89Medium
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.90Medium
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.91Hard
The anatomical adaptation of the leaf of Nerium (oleander) for xerophytic conditions includes all of the following EXCEPT:
Answer: C
Xerophytes like Nerium have reduced intercellular spaces (not large) to minimize water loss. They have sunken stomata, thick cuticle, and multiple palisade layers.
Q.92Hard
Which statement best describes the relationship between vessel elements and tracheids in angiosperm xylem?
Answer: A
Vessel elements in angiosperms have perforations (lacking end walls) allowing efficient water transport, while tracheids with bordered pits provide both transport and mechanical support.
Q.93Medium
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.94Medium
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.95Hard
The anatomical basis for the high tensile strength of wood in dicots is primarily due to:
Answer: B
Xylem fibers, which constitute a significant portion of secondary xylem, have thick lignified walls that provide tensile strength to the wood.
Q.96Hard
In the phloem, sieve plate perforations serve the function of:
Answer: A
Sieve plate perforations with reduced cell wall material allow efficient translocation of assimilates between sieve tube elements with minimal resistance.
Q.97Easy
The primary function of root hair cells is to:
Answer: B
Root hairs are unicellular extensions of root epidermis that greatly increase absorptive surface area for water and mineral uptake.
Q.98Medium
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.99Medium
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.
Q.100Hard
During the development of a dicot leaf, the dorsiventral structure is established with palisade parenchyma on the adaxial surface and spongy mesophyll on the abaxial surface. Which combination of factors is primarily responsible for maintaining this distinct anatomical differentiation?
Answer: A
The dorsiventral structure of dicot leaves is primarily established by differential light exposure (adaxial surface receives more direct light, promoting compact palisade development) combined with auxin gradients that influence cell differentiation patterns. The abaxial surface, receiving diffuse light and lower auxin concentration, develops the loosely packed spongy mesophyll with intercellular spaces for gas exchange.
