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1. Which statement best defines meristematic tissue in flowering plants?
ⓐ. A tissue composed of elongated cells that transport sugars through sieve tubes
ⓑ. A group of dead cells that mainly provide mechanical strength to mature organs
ⓒ. A tissue made of loosely arranged living cells for gaseous exchange in leaves
ⓓ. A group of living cells that actively divide to produce new cells for growth
Correct Answer: A group of living cells that actively divide to produce new cells for growth
Explanation: Meristematic tissue consists of living, undifferentiated cells that retain the ability to divide continuously, making it the source of new cells in a plant body. These cells are typically small, with thin primary walls, dense cytoplasm, and a prominent nucleus, reflecting high metabolic activity. Because they keep dividing, they directly contribute to plant growth, either increasing length (primary growth) or thickness (secondary growth). Meristems also give rise to permanent tissues after differentiation. This continuous cell division property is the defining feature that separates meristematic tissue from mature tissues. Hence, meristematic tissue is fundamentally a growth-forming, actively dividing tissue system.
2. A student observes many air spaces between loosely arranged cells in a leaf’s internal tissue. Which tissue is most consistent with this observation?
ⓐ. Collenchyma
ⓑ. Parenchyma (spongy mesophyll type)
ⓒ. Sclerenchyma
ⓓ. Phloem parenchyma
Correct Answer: Parenchyma (spongy mesophyll type)
Explanation: Spongy mesophyll is a specialized form of parenchyma found in leaves where cells are loosely packed with conspicuous intercellular spaces. These air spaces facilitate efficient diffusion of gases like CO₂ and O₂ during photosynthesis and respiration. The cells are living, typically thin-walled, and may contain chloroplasts, though fewer than palisade cells. The “spongy” arrangement is an anatomical adaptation to maximize internal gas exchange rather than mechanical support. This directly matches the observation of abundant air spaces among loosely arranged cells. Therefore, the tissue is best identified as spongy mesophyll parenchyma.
3. Which combination correctly lists the main elements of xylem tissue in flowering plants?
ⓐ. Sieve tubes, companion cells, phloem fibres, phloem parenchyma
ⓑ. Tracheids, vessel elements, xylem fibres, xylem parenchyma
ⓒ. Epidermal cells, guard cells, trichomes, root hairs
ⓓ. Collenchyma, sclerenchyma, parenchyma, aerenchyma
Correct Answer: Tracheids, vessel elements, xylem fibres, xylem parenchyma
Explanation: Xylem is a complex tissue primarily responsible for water and mineral transport and also contributes to support. Its conducting elements are tracheids and vessel elements, which are typically dead at maturity and possess thickened, lignified walls suited for conduction and strength. Xylem fibres add mechanical support, while xylem parenchyma consists of living cells involved in storage and lateral transport. This set of four components is a standard anatomical description of xylem in flowering plants. The other options list phloem elements or protective tissues rather than xylem constituents. Hence, the correct combination is tracheids, vessel elements, xylem fibres, and xylem parenchyma.
4. In phloem, what is the most accurate role of companion cells in relation to sieve tube elements?
ⓐ. They deposit lignin to strengthen sieve tubes for high-pressure water flow
ⓑ. They store starch as the main long-term reserve for the entire phloem
ⓒ. They provide metabolic support and help in loading/unloading of sugars in sieve tubes
ⓓ. They form openings (pits) to enable upward movement of water through phloem
Correct Answer: They provide metabolic support and help in loading/unloading of sugars in sieve tubes
Explanation: Sieve tube elements in flowering plants are living but have reduced cellular contents at maturity, including the absence of a nucleus, so they depend on companion cells for metabolic regulation. Companion cells are closely associated with sieve tubes through plasmodesmata, allowing exchange of signals and metabolites. They are crucial in the active loading and unloading of sugars and other organic solutes, enabling efficient translocation. This functional partnership maintains sieve tube viability and supports pressure-driven transport of food materials. Lignification and water conduction are xylem-related features, not phloem roles. Therefore, companion cells primarily provide metabolic support and assist sugar movement in sieve tubes.
5. Which feature most reliably distinguishes collenchyma from sclerenchyma in flowering plants?
ⓐ. Collenchyma cells are living with unevenly thickened primary walls, often at corners
ⓑ. Collenchyma cells are dead with uniformly lignified secondary walls for rigidity
ⓒ. Collenchyma occurs only in roots, while sclerenchyma occurs only in leaves
ⓓ. Collenchyma is a complex tissue with vessels, while sclerenchyma is simple tissue
Correct Answer: Collenchyma cells are living with unevenly thickened primary walls, often at corners
Explanation: Collenchyma is a living simple permanent tissue that provides flexible mechanical support, especially in growing parts like young stems and petioles. Its hallmark is uneven thickening of the primary cell wall, commonly at the corners, due to cellulose and pectin, which allows strength without restricting growth. In contrast, sclerenchyma typically consists of dead cells at maturity with thick, lignified secondary walls, providing rigid support. The living nature and uneven primary wall thickening make collenchyma distinct in both structure and functional biomechanics. Collenchyma is not limited to roots, and it is not a complex tissue. Thus, the distinguishing feature is living cells with uneven primary wall thickening.
6. A transverse section shows vascular bundles arranged in a ring with a distinct pith in the center. Which organ and plant group is most consistent with this pattern?
ⓐ. Monocot root
ⓑ. Monocot stem
ⓒ. Dicot stem
ⓓ. Dicot root
Correct Answer: Dicot stem
Explanation: In a typical dicot stem, vascular bundles are arranged in a ring surrounding a well-developed central pith. This ring arrangement supports organized conduction and provides a framework for secondary growth because the bundles are usually open (with cambium). Monocot stems generally have scattered vascular bundles, not a ring, while roots show a different radial arrangement of xylem and phloem rather than discrete bundles in a ring. The presence of a distinct pith along with ring-arranged bundles strongly points to a dicot stem anatomy. This pattern is a classic diagnostic feature used in practical identification. Therefore, the section most consistently represents a dicot stem.
7. In many dicot roots, the xylem commonly shows which arrangement in the central region?
ⓐ. A ring of separate collateral vascular bundles around a large pith
ⓑ. Scattered vascular bundles embedded in ground tissue without a clear center
ⓒ. Star-shaped xylem with phloem located between the arms (radial arrangement)
ⓓ. A continuous phloem cylinder inside and xylem only at the periphery
Correct Answer: Star-shaped xylem with phloem located between the arms (radial arrangement)
Explanation: Dicot roots characteristically have a radial arrangement of vascular tissues, where xylem and phloem lie on different radii. The xylem often forms a star-like shape in the center, and the phloem patches are positioned between the xylem arms. This configuration supports efficient conduction and is a key feature distinguishing roots from stems in transverse sections. Unlike stems, roots do not typically show discrete collateral bundles arranged in a ring. Scattered bundles are more typical of monocot stems, not dicot roots. Hence, the correct arrangement is star-shaped central xylem with phloem between its arms.
8. Which statement correctly describes stomata in the context of epidermal tissue?
ⓐ. Stomata are permanent openings in xylem vessels that enable transpiration pull
ⓑ. Stomata are pores in epidermis controlled by guard cells to regulate gas exchange and water loss
ⓒ. Stomata are holes made by insects that increase diffusion of oxygen into roots
ⓓ. Stomata are spaces between collenchyma cells that store carbon dioxide for photosynthesis
Correct Answer: Stomata are pores in epidermis controlled by guard cells to regulate gas exchange and water loss
Explanation: Stomata are specialized epidermal structures consisting of a pore bordered by guard cells, and often supported by subsidiary cells. By changing their turgor, guard cells open or close the pore, thereby regulating CO₂ entry for photosynthesis and controlling water vapor loss via transpiration. This regulation is essential for maintaining water balance while allowing gas exchange. Stomata are not part of xylem or collenchyma and are not random damage-related openings. Their placement within the epidermis links them to the protective tissue system with a key physiological function. Therefore, stomata are epidermal pores controlled by guard cells for gas exchange and transpiration regulation.
9. In secondary growth, which tissue is directly responsible for producing secondary xylem and secondary phloem?
ⓐ. Apical meristem
ⓑ. Intercalary meristem
ⓒ. Vascular cambium
ⓓ. Cork cambium
Correct Answer: Vascular cambium
Explanation: Vascular cambium is a lateral meristem that forms a continuous ring (or near-continuous in older regions) and divides to add tissues on both sides. It produces secondary xylem toward the inside and secondary phloem toward the outside, increasing the girth of stems and roots. This activity is the central mechanism of secondary growth in many dicots and gymnosperms. Apical and intercalary meristems primarily drive elongation, not thickening, while cork cambium forms periderm components like cork. The bidirectional production of conducting tissues is the unique role of vascular cambium. Hence, vascular cambium is responsible for secondary xylem and secondary phloem formation.
10. Which tissue is best identified by thick-walled, lignified cells that are dead at maturity and commonly form fibres in seed coats and around vascular bundles?
ⓐ. Aerenchyma
ⓑ. Parenchyma
ⓒ. Collenchyma
ⓓ. Sclerenchyma
Correct Answer: Sclerenchyma
Explanation: Sclerenchyma is a simple permanent tissue specialized for mechanical strength, characterized by very thick, lignified secondary walls. Its cells are typically dead at maturity, leaving a narrow lumen, and occur as fibres or sclereids in various plant parts. Fibres commonly provide tensile strength around vascular bundles and contribute to hardness in structures like seed coats. This lignified, dead-at-maturity nature makes sclerenchyma especially suited for rigid support and protection. Aerenchyma is an air-space parenchyma, parenchyma is living and thin-walled, and collenchyma is living with uneven primary wall thickening. Therefore, the tissue described is sclerenchyma.
11. Which statement best describes the primary role of apical meristem in a flowering plant?
ⓐ. It increases the girth of stems and roots by forming secondary tissues
ⓑ. It produces new cells that elongate the plant body at shoot and root tips
ⓒ. It forms the protective cork layer by producing suberized outer cells
ⓓ. It stores food and water in mature organs as thin-walled living cells
Correct Answer: It produces new cells that elongate the plant body at shoot and root tips
Explanation: Apical meristem is located at the growing tips of roots and shoots, where its actively dividing cells continuously add new cells to the plant body. These new cells undergo elongation and differentiation, resulting in primary growth, which increases the length of stems and roots. This is why young regions near the tips show rapid extension compared to older parts. The tissues formed from apical meristem contribute to the plant’s primary tissue systems such as epidermis, ground tissue, and primary vascular tissues. Girth increase is mainly due to lateral meristems, not apical meristems. Therefore, apical meristem’s key role is elongation of plant organs.
12. A seedling shows faster growth in length at the shoot tip compared to the older stem region. Which feature most directly explains this difference?
ⓐ. Cells at the shoot tip are dedifferentiated and actively mitotic, producing new cells for elongation
ⓑ. Cells in the older stem region have higher photosynthetic rate, causing rapid extension
ⓒ. Cells at the shoot tip have thick lignified walls, making them expand more quickly
ⓓ. Cells in the older stem region have larger vacuoles, preventing any growth at the tip
Correct Answer: Cells at the shoot tip are dedifferentiated and actively mitotic, producing new cells for elongation
Explanation: The shoot tip contains apical meristematic cells that remain undifferentiated and retain continuous mitotic activity. This constant production of new cells provides the raw material for elongation as newly formed cells enlarge and differentiate into primary tissues. Older stem regions mainly consist of mature, differentiated cells with limited or no capacity for division, so extension growth is much reduced there. Thick lignified walls typically restrict expansion rather than accelerate it, and photosynthesis does not directly create length increase without meristematic cell production. The difference in growth rate is therefore explained by active mitosis and cell addition at the shoot apex. Hence, the shoot tip grows faster because apical meristem keeps generating new cells.
13. Which of the following is the most accurate location of apical meristem in flowering plants?
ⓐ. At the nodes of stem where leaves attach
ⓑ. At the margins of mature leaves
ⓒ. At the tips of roots and shoots in the growing regions
ⓓ. Around the vascular bundles of mature stem
Correct Answer: At the tips of roots and shoots in the growing regions
Explanation: Apical meristems are positioned at the terminal ends of shoots and roots, forming the main centers of primary growth. Their placement at the tips ensures that new cells are added ahead of older tissues, allowing the plant to extend into new space and explore soil and light environments. In roots, the apical meristem lies just behind the root cap and supplies cells for root elongation and tissue formation. In shoots, it forms new stem segments and initiates leaf and bud primordia. Nodes and mature regions do not typically house apical meristems responsible for primary elongation. Therefore, the correct location is at the growing tips of roots and shoots.
14. In the root tip, the immediate protective structure covering the apical meristem is best identified as:
ⓐ. Endodermis
ⓑ. Cortex
ⓒ. Pericycle
ⓓ. Root cap
Correct Answer: Root cap
Explanation: The root cap is a protective tissue at the very tip of the root that shields the delicate apical meristem from mechanical damage as the root pushes through soil. It also secretes mucilage, which lubricates the root tip and aids penetration into the substrate. Additionally, the root cap plays a role in gravity perception, helping direct root growth. The apical meristem lies just behind the root cap, ensuring new cells can be produced safely while the cap takes the abrasive contact. Endodermis, pericycle, and cortex are internal tissues not positioned as the tip’s protective covering. Hence, the immediate protective structure for the root apical meristem is the root cap.
15. Which statement best captures why apical meristem cells typically have dense cytoplasm and a prominent nucleus?
ⓐ. They are primarily storing starch and oils for long-term survival
ⓑ. They are metabolically active and continuously dividing, requiring strong genetic and enzymatic control
ⓒ. They are specialized for rapid water conduction through large hollow spaces
ⓓ. They are dead at maturity and thickened to provide rigidity at the growing tip
Correct Answer: They are metabolically active and continuously dividing, requiring strong genetic and enzymatic control
Explanation: Apical meristematic cells remain in an actively dividing state, so they must maintain high metabolic activity to support DNA replication, mitosis, and synthesis of cellular components. Dense cytoplasm reflects abundant organelles and enzymes needed for biosynthesis, while a prominent nucleus supports intense control of gene expression and cell cycle regulation. These cells usually have minimal vacuolation because large vacuoles are more typical of mature cells involved in storage and turgor-based expansion. Conducting tissues like xylem are typically dead at maturity and hollow, which is not the case for meristematic cells. The structural and biochemical profile of meristem cells is therefore aligned with continuous division. Hence, dense cytoplasm and a prominent nucleus indicate metabolically active, dividing apical meristem cells.
16. A plant is experimentally treated so that cell division at the shoot tip stops, but mature leaves still photosynthesize normally. What is the most likely immediate growth outcome?
ⓐ. Increase in stem thickness due to enhanced cambium activity at the tip
ⓑ. Continued rapid increase in plant height because photosynthesis alone drives elongation
ⓒ. Little to no increase in plant height because new cells for elongation are not produced at the apex
ⓓ. Formation of extra root caps because shoot apical meristem converts into root meristem
Correct Answer: Little to no increase in plant height because new cells for elongation are not produced at the apex
Explanation: Primary increase in plant height depends on continuous production of new cells by the shoot apical meristem, followed by their elongation and differentiation. If mitotic activity at the shoot tip stops, the plant cannot add new stem segments or initiate normal extension growth, even if photosynthesis continues to supply sugars. Photosynthesis provides energy and raw materials, but without active cell division at the apex, those resources cannot be converted into new tissues that extend the shoot. Stem thickening is mainly linked to lateral meristems in mature regions, not an inactive shoot tip. The most immediate effect is therefore reduced or halted increase in height. Hence, stopping apical meristem division leads to little or no further height growth.
17. Which pairing most correctly matches an apical meristem with a key developmental output?
ⓐ. Root apical meristem → formation of cork and bark in old roots
ⓑ. Shoot apical meristem → initiation of leaves and lateral buds along with stem elongation
ⓒ. Root apical meristem → production of annual rings in woody stems
ⓓ. Shoot apical meristem → transport of sugars through sieve tubes as the main function
Correct Answer: Shoot apical meristem → initiation of leaves and lateral buds along with stem elongation
Explanation: The shoot apical meristem drives primary growth of the shoot by producing new stem tissues and initiating organ primordia such as leaves and axillary (lateral) buds. This meristem maintains a pool of dividing cells that both extend the shoot axis and generate new aerial organs in an organized pattern. Cork and bark formation is associated with cork cambium, and annual rings result from vascular cambium activity, not apical meristems. Sugar transport is a function of phloem tissues rather than a meristem’s primary role. Therefore, the correct developmental output linked to the shoot apical meristem is leaf and bud initiation along with elongation. Hence, the most accurate pairing is shoot apical meristem with formation of leaves, lateral buds, and stem extension.
18. In a typical root tip, the correct order from the extreme tip toward the older region is best represented as:
ⓐ. Zone of maturation → zone of elongation → zone of cell division → root cap
ⓑ. Zone of elongation → root cap → zone of cell division → zone of maturation
ⓒ. Root cap → zone of maturation → zone of elongation → zone of cell division
ⓓ. Root cap → zone of cell division → zone of elongation → zone of maturation
Correct Answer: Root cap → zone of cell division → zone of elongation → zone of maturation
Explanation: The extreme root tip is covered by the root cap, which protects the growing region. Just behind it lies the zone of cell division where the root apical meristem actively produces new cells. These newly formed cells then enter the zone of elongation, where they rapidly increase in length, pushing the root tip forward. Farther back is the zone of maturation (differentiation), where cells specialize into tissues and root hairs often appear for absorption. This sequential arrangement reflects how roots grow: protect, produce, elongate, then differentiate. Therefore, the correct order is root cap, cell division, elongation, and maturation.
19. Which feature is most characteristic of apical meristematic cells compared to mature permanent cells?
ⓐ. Large intercellular spaces and extensive air cavities for gas exchange
ⓑ. Thick suberized walls that block water movement through tissues
ⓒ. Thin primary cell walls with closely packed cells and minimal intercellular spaces
ⓓ. Highly lignified secondary walls and hollow interiors for conduction
Correct Answer: Thin primary cell walls with closely packed cells and minimal intercellular spaces
Explanation: Apical meristematic cells are designed for continuous division and are therefore small, closely packed, and typically lack prominent intercellular spaces. They possess thin primary cell walls that allow formation of new cell plates and expansion during early growth stages. Their compact arrangement supports coordinated tissue formation and maintains the integrity of the growing tip. Features like large air spaces are more typical of specialized parenchyma in certain organs, suberized walls relate to protective tissues, and lignified hollow structures are typical of xylem elements. The key diagnostic combination in meristems is thin walls, dense cytoplasm, and compact cell packing. Hence, thin primary walls with minimal intercellular spaces best characterizes apical meristem cells.
20. A gardener trims the shoot tip of a young plant and notices increased growth of side branches over time. Which explanation best fits this outcome in terms of apical meristem function?
ⓐ. Removal of the shoot apical meristem reduces dominance, allowing axillary buds to grow into branches
ⓑ. Cutting the tip increases xylem formation immediately, forcing lateral branching
ⓒ. Trimming converts leaf parenchyma into cambium, producing more branches
ⓓ. Removal of the tip stops all growth permanently because meristems exist only at one point
Correct Answer: Removal of the shoot apical meristem reduces dominance, allowing axillary buds to grow into branches
Explanation: The shoot apical meristem helps maintain apical dominance, a growth pattern where the main shoot suppresses the outgrowth of axillary buds. When the shoot tip is removed, the influence of the apex decreases, and axillary buds can resume active growth to form lateral branches. This is widely used in horticulture to promote bushier plants by redirecting growth from the main axis to side shoots. The effect is regulatory and developmental rather than a direct increase in xylem or conversion of mature tissues into cambium. Growth does not stop permanently because plants have multiple meristems, including axillary buds. Therefore, increased side branching after trimming is explained by reduced apical dominance due to removal of the shoot apical meristem.
21. Intercalary meristem is most commonly located in which region of flowering plants (especially grasses)?
ⓐ. At the extreme tip of root just behind the root cap
ⓑ. At the base of leaves or at nodes/internodes near the leaf base
ⓒ. In the cork-forming layer of older stems beneath the epidermis
ⓓ. In the vascular bundles as a ring between xylem and phloem
Correct Answer: At the base of leaves or at nodes/internodes near the leaf base
Explanation: Intercalary meristem occurs between mature tissues, typically near nodes and at the base of leaves or internodes, especially in many monocots like grasses. Its position allows the plant to continue elongation in specific segments even when the terminal growing tip is damaged or removed. Because it is embedded in regions that may already show partial differentiation, it supports rapid lengthening of internodes and leaf bases. This is why grasses can quickly regain height after cutting or grazing. It is not a cambium ring involved in secondary growth, and it is not confined to root tips. Hence, the correct location is the base of leaves or nodal/internodal regions near the leaf base.
22. A lawn recovers quickly after repeated mowing because new growth continues from a meristematic region near the leaf base. Which meristem explains this regrowth most directly?
ⓐ. Apical meristem
ⓑ. Lateral meristem
ⓒ. Pericycle
ⓓ. Intercalary meristem
Correct Answer: Intercalary meristem
Explanation: In many grasses, the actively dividing meristematic cells responsible for elongation remain near the base of leaves and internodes, forming intercalary meristems. When mowing removes the upper portions, these basal meristems are left intact and continue producing new cells that elongate the leaf or internode. This arrangement is an adaptive advantage in habitats exposed to grazing or cutting. Because growth is driven from a region not easily removed, regrowth is rapid and repeated. Lateral meristems mainly increase girth, and pericycle is a root tissue associated with lateral root formation. Therefore, intercalary meristem best explains the rapid recovery after mowing.
23. Which statement most accurately distinguishes intercalary meristem from apical meristem?
ⓐ. Intercalary meristem is located between mature tissues and contributes to elongation of internodes/leaf bases
ⓑ. Intercalary meristem forms secondary xylem and secondary phloem to increase thickness
ⓒ. Intercalary meristem is found only in dicot roots and produces root hairs directly
ⓓ. Intercalary meristem is composed of dead, lignified cells that provide rigidity
Correct Answer: Intercalary meristem is located between mature tissues and contributes to elongation of internodes/leaf bases
Explanation: Intercalary meristems are positioned away from the organ tip, commonly at nodes or the base of leaves and internodes, and they function mainly in lengthening those regions. Apical meristems, in contrast, occupy the growing tips and drive overall primary growth of shoots and roots from the apex. Intercalary meristems are particularly notable in many monocots, supporting rapid segment-wise elongation and regrowth after injury. They do not produce secondary vascular tissues; that role belongs to vascular cambium. They are living, actively dividing tissues, not dead lignified support cells. Hence, the key distinction is their between-mature-tissues location and their role in elongating internodes/leaf bases.
24. In many flowering plants that show intercalary meristems, these meristems are best understood as:
ⓐ. Newly formed meristems produced only after wounding of mature tissues
ⓑ. Permanent storage tissues that later regain the ability to divide
ⓒ. Remnants of apical meristem left behind during elongation and differentiation
ⓓ. The same as vascular cambium but positioned at nodes for faster thickening
Correct Answer: Remnants of apical meristem left behind during elongation and differentiation
Explanation: Intercalary meristems are commonly interpreted as portions of primary meristematic tissue that remain meristematic even as surrounding cells differentiate during growth. As the shoot elongates, certain meristematic regions persist at nodal or basal positions, effectively acting as “left-behind” segments of the original primary growth machinery. This explains why they can continue cell division and elongation in specific regions between mature tissues. Their presence supports rapid extension growth without relying solely on the terminal apex. They are not equivalent to cambium and do not primarily cause thickening. Therefore, they are best described as remnants of apical meristem retained in basal/nodal regions.
25. Which growth process is most directly driven by intercalary meristem activity?
ⓐ. Increase in girth due to secondary growth in woody stems
ⓑ. Formation of cork and periderm on older plant parts
ⓒ. Elongation of internodes and leaf bases, especially in grasses
ⓓ. Development of annual rings by alternating xylem production
Correct Answer: Elongation of internodes and leaf bases, especially in grasses
Explanation: Intercalary meristems contribute to primary growth by adding new cells that elongate particular regions such as internodes and leaf bases. This localized elongation is especially prominent in grasses, where growth zones near the base remain active and allow rapid vertical regrowth after cutting. The process is primarily length increase, not thickness increase. Cork and periderm formation are produced by cork cambium, while annual rings arise from vascular cambium activity. The functional hallmark of intercalary meristem is therefore segment-wise elongation in positions away from the tip. Hence, elongation of internodes and leaf bases is the growth process most directly driven by intercalary meristems.
26. A sugarcane plant shows rapid elongation of internodes even when the upper shoot region is partially damaged. Which meristem most plausibly sustains this internodal growth?
ⓐ. Root apical meristem pushing the shoot upward
ⓑ. Cork cambium beneath the epidermis of old stems
ⓒ. Vascular cambium ring producing secondary tissues
ⓓ. Intercalary meristem at or near nodes/internodes
Correct Answer: Intercalary meristem at or near nodes/internodes
Explanation: In plants like sugarcane and many grasses, internodal elongation is strongly supported by intercalary meristems located near nodes or at the base of internodes. Because these growth zones are not restricted to the terminal tip, they can continue producing and elongating cells even if the upper shoot region is damaged. This explains sustained internode extension and rapid recovery of height. Cork cambium forms protective outer tissues and does not drive elongation. Vascular cambium primarily increases thickness, not internode length. Therefore, intercalary meristem near nodes/internodes is the most plausible driver of continued internodal growth in such cases.
27. Which feature is most characteristic of intercalary meristematic cells, consistent with their active division?
ⓐ. Wide intercellular spaces for gas storage and diffusion
ⓑ. Dense cytoplasm with prominent nuclei and thin primary walls
ⓒ. Dead cells with thick lignified secondary walls for mechanical strength
ⓓ. Suberized walls that block water movement across tissues
Correct Answer: Dense cytoplasm with prominent nuclei and thin primary walls
Explanation: Intercalary meristems consist of living, actively dividing cells, so they display typical meristematic features: dense cytoplasm, a prominent nucleus, and thin primary walls. These attributes reflect high metabolic activity needed for DNA replication, mitosis, and synthesis of new cellular material. The thin primary wall supports new cell formation and early expansion before differentiation. Large intercellular spaces are associated with certain parenchyma types rather than meristems. Lignified dead cells and suberized walls are features of mature protective or supportive tissues, not dividing zones. Hence, dense cytoplasm with prominent nuclei and thin primary walls best characterizes intercalary meristem cells.
28. Which statement best describes the contribution of intercalary meristem to plant survival in grazed habitats?
ⓐ. It promotes rapid regrowth by keeping active dividing tissue near the base, reducing loss during grazing
ⓑ. It prevents all herbivory by producing toxic compounds in the leaf epidermis
ⓒ. It increases stem thickness quickly so the plant cannot be eaten easily
ⓓ. It stops water loss by forming a thick cork layer over leaf surfaces
Correct Answer: It promotes rapid regrowth by keeping active dividing tissue near the base, reducing loss during grazing
Explanation: Intercalary meristems confer an ecological advantage in plants frequently exposed to grazing or cutting by positioning active growth zones near the base of leaves or internodes. When an herbivore removes the upper parts, the basal meristematic tissue often remains intact and can rapidly produce new cells for elongation. This enables quick recovery of photosynthetic surface area and plant height, improving survival and competitiveness. The strategy is primarily anatomical and developmental rather than based on toxin production or cork formation. Thickening is not the main immediate response in such plants. Therefore, basal placement of active dividing tissue for rapid regrowth is the key survival contribution of intercalary meristems.
29. Intercalary meristems are most strongly associated with which type of plant based on typical anatomical occurrence?
ⓐ. Many monocots, especially grasses, where growth zones persist near nodes and leaf bases
ⓑ. Woody dicots, where secondary growth dominates and elongation stops early
ⓒ. Aquatic plants only, because air storage requires basal meristems
ⓓ. Gymnosperms only, because they lack true apical meristems
Correct Answer: Many monocots, especially grasses, where growth zones persist near nodes and leaf bases
Explanation: Intercalary meristems are classically prominent in many monocotyledonous plants, particularly grasses, where basal and nodal growth zones remain active. This is linked to their growth habit, allowing continuous elongation of leaves and internodes and rapid regrowth after clipping. While some other groups may show localized meristematic regions, the strongest and most commonly tested association is with monocots like grasses. Woody dicots are more commonly discussed in relation to secondary growth via lateral meristems rather than intercalary growth zones. Aquatic habitat is not the defining condition for intercalary meristems. Hence, many monocots, especially grasses, are most strongly associated with intercalary meristems.
30. If an intercalary meristem at the base of a grass leaf is experimentally inactivated, what is the most likely direct effect on that leaf?
ⓐ. The leaf loses all chlorophyll immediately and turns white
ⓑ. The leaf base develops cork and becomes impermeable
ⓒ. The leaf stops increasing in length because new cells for elongation are no longer produced at the base
ⓓ. The leaf begins secondary thickening by forming annual rings within the lamina
Correct Answer: The leaf stops increasing in length because new cells for elongation are no longer produced at the base
Explanation: Intercalary meristems at the leaf base supply new cells that subsequently elongate, driving continued length increase of the leaf. If this meristematic region is inactivated, the leaf cannot add new cells in that growth zone, so further elongation is greatly reduced or stops. Photosynthetic function may continue in existing tissues for some time, but growth in length depends on ongoing cell division and expansion initiated from the basal meristem. Cork formation and annual rings are unrelated to leaf lamina growth and are not expected outcomes in this context. The most direct and immediate impact is therefore loss of length growth. Hence, inactivating the intercalary meristem causes the leaf to stop increasing in length.
31. In a typical dicot stem, which statement best describes the main function of lateral meristem?
ⓐ. It increases length by adding new cells at shoot and root tips
ⓑ. It forms root hairs by differentiating epidermal cells in the maturation zone
ⓒ. It conducts sugars by forming sieve tubes and companion cells in primary phloem
ⓓ. It increases girth by producing secondary tissues that add thickness to stems and roots
Correct Answer: It increases girth by producing secondary tissues that add thickness to stems and roots
Explanation: Lateral meristems are meristematic tissues arranged parallel to the sides of stems and roots, and their defining role is secondary growth, i.e., increase in thickness. They divide mainly in a tangential plane to add new cells outward and inward, which later differentiate into secondary tissues. This activity strengthens the plant body and supports greater transport capacity by expanding vascular tissues. In many flowering plants, this is essential for forming woody stems and robust roots. Length increase is primarily controlled by apical and intercalary meristems, not lateral ones. Therefore, the core function of lateral meristem is increasing girth via secondary tissue production.
32. Vascular cambium contributes to secondary growth by directly producing:
ⓐ. Cork outward and phelloderm inward
ⓑ. Secondary xylem inward and secondary phloem outward
ⓒ. Epidermis and cuticle to protect older stems
ⓓ. Cortex and endodermis to regulate radial water movement
Correct Answer: Secondary xylem inward and secondary phloem outward
Explanation: Vascular cambium is a lateral meristem located between xylem and phloem (in regions where it forms a ring or continuous cambial zone). Its periclinal divisions generate new vascular cells on both sides: cells added to the inner side differentiate into secondary xylem (wood), while those added to the outer side become secondary phloem. This bidirectional production increases the conducting capacity and mechanical strength of the plant over time. The process is central to thickening in many dicot stems and roots. Cork and phelloderm are produced by cork cambium, not vascular cambium. Hence, vascular cambium produces secondary xylem inward and secondary phloem outward.
33. Which option best describes the primary function of cork cambium (phellogen)?
ⓐ. It forms periderm by producing cork (phellem) to the outside and phelloderm to the inside
ⓑ. It produces secondary xylem and secondary phloem to increase transport capacity
ⓒ. It increases organ length by adding cells at the tip that later elongate
ⓓ. It forms sieve plates and controls food transport through phloem
Correct Answer: It forms periderm by producing cork (phellem) to the outside and phelloderm to the inside
Explanation: Cork cambium (phellogen) is a lateral meristem that replaces the epidermis in older stems and roots as they expand. It divides to produce cork cells (phellem) on the outer side, which develop suberized walls and reduce water loss and pathogen entry, and it produces phelloderm on the inner side, which remains living and can contribute to storage or support. Together, these tissues constitute the periderm, a major protective covering in mature organs undergoing secondary growth. This function is protective rather than conductive, and it is distinct from vascular cambium’s role in making secondary xylem and phloem. Therefore, the key function of cork cambium is periderm formation via cork and phelloderm production.
34. A woody stem shows a thick “wood” region formed over years. This wood is mainly:
ⓐ. Secondary phloem produced outward by vascular cambium
ⓑ. Primary xylem produced early during elongation growth
ⓒ. Secondary xylem produced inward by vascular cambium
ⓓ. Periderm produced by cork cambium beneath the epidermis
Correct Answer: Secondary xylem produced inward by vascular cambium
Explanation: In woody stems, the bulk of the thick internal cylinder called wood is composed primarily of secondary xylem. This tissue is generated year after year by the vascular cambium on its inner side, leading to a large accumulation of xylem elements and supporting fibers. Secondary xylem functions in water and mineral conduction and provides strong mechanical support due to lignified cell walls. Primary xylem is present but forms a much smaller portion compared to the massive secondary xylem in woody plants. Periderm is an outer protective covering and does not constitute wood. Hence, wood is mainly secondary xylem produced inward by vascular cambium.
35. During secondary growth, why does secondary phloem not accumulate as massively as secondary xylem in older stems?
ⓐ. Secondary phloem is continuously crushed and sloughed off as new tissues form outward, limiting long-term accumulation
ⓑ. Secondary phloem is converted into xylem each season by reversing cambial activity
ⓒ. Secondary phloem quickly becomes hollow and merges into the pith region
ⓓ. Secondary phloem is never produced in dicot stems; only primary phloem is present
Correct Answer: Secondary phloem is continuously crushed and sloughed off as new tissues form outward, limiting long-term accumulation
Explanation: Vascular cambium produces secondary phloem outward, but as secondary xylem accumulates inward, the stem’s circumference expands and compresses older outer tissues. Secondary phloem, being positioned toward the outside, is subjected to stretching and compression, and much of the older phloem becomes crushed and functionally inactive over time. Additionally, protective tissues formed outside (periderm and successive bark layers) can lead to shedding of older outer regions, further limiting phloem buildup. In contrast, secondary xylem is retained and continuously added to the inner side, so it accumulates greatly. This anatomical consequence of position explains the unequal accumulation. Therefore, secondary phloem does not pile up like xylem because it is compressed and often shed.
36. Which change is most directly explained by lateral meristem activity in a dicot root as the plant matures?
ⓐ. The root becomes thicker due to formation of secondary xylem and secondary phloem
ⓑ. The root cap becomes larger to protect the dividing cells at the tip
ⓒ. The root increases length rapidly because cells divide only at the apex
ⓓ. More stomata appear on the root surface to enhance gas exchange
Correct Answer: The root becomes thicker due to formation of secondary xylem and secondary phloem
Explanation: In many dicot roots, secondary growth occurs when lateral meristems become active—primarily the vascular cambium, which develops and produces secondary xylem inward and secondary phloem outward. This process increases the root’s girth, improving transport capacity and mechanical anchorage. With increasing diameter, the original outer tissues often get replaced by protective periderm formed by cork cambium, another lateral meristem. The root cap is associated with primary growth at the tip, not thickening of mature regions. Stomata are generally absent on roots, and length increase is driven by apical meristem. Hence, lateral meristem activity most directly explains increased root thickness via secondary vascular tissue formation.
37. A stem segment forms a protective covering that replaces the epidermis during thickening. Which function most precisely fits the tissues produced by cork cambium?
ⓐ. Long-distance transport of sugars under pressure flow
ⓑ. Reduction of water loss and entry of pathogens through a suberized outer barrier
ⓒ. Primary elongation by continuous cell division at the growing tip
ⓓ. Absorption of water using thin-walled epidermal hairs
Correct Answer: Reduction of water loss and entry of pathogens through a suberized outer barrier
Explanation: Cork cambium produces cork cells (phellem) toward the outside, and these cells develop suberin in their walls, making them relatively impermeable to water and gases. This creates a protective barrier that minimizes desiccation and blocks pathogen entry, especially important as organs expand and the epidermis can no longer remain intact. The periderm formed by cork cambium thus serves as a replacement protective tissue system in older regions. While this barrier restricts gas exchange, specialized openings can develop to maintain limited exchange. Sugar transport is a phloem function, and absorption is mainly by root hairs in young roots. Therefore, the most precise function is forming a suberized protective barrier that reduces water loss and pathogen invasion.
38. In secondary growth, rays (vascular or medullary rays) are most directly important for:
ⓐ. Upward conduction of water through continuous vessel columns
ⓑ. Protecting the root tip from friction in soil
ⓒ. Opening and closing stomata to regulate transpiration
ⓓ. Lateral transport of water and food, and storage across the stem radius
Correct Answer: Lateral transport of water and food, and storage across the stem radius
Explanation: Rays are radial bands of parenchyma that extend from inner regions outward through secondary xylem and secondary phloem. Their main significance lies in facilitating lateral (radial) movement of water, minerals, and organic solutes between different tissues, complementing the vertical transport performed by xylem and phloem. Rays also serve as storage sites for starch and other reserves, contributing to seasonal physiology and repair. Because secondary growth adds tissues in concentric layers, rays maintain functional connectivity across these layers. Stomatal control and root cap protection are unrelated to rays. Hence, rays are crucial for radial transport and storage across the stem or root.
39. Which observation most strongly indicates active lateral meristem function in a stem rather than only primary growth?
ⓐ. New leaves are initiated at the shoot tip
ⓑ. Root hairs appear in the maturation zone of roots
ⓒ. A continuous cambial ring forms and the stem diameter increases over time
ⓓ. Cells in the cortex become loosely arranged, creating large air spaces
Correct Answer: A continuous cambial ring forms and the stem diameter increases over time
Explanation: A hallmark of lateral meristem function is secondary growth, which manifests as progressive increase in stem or root diameter. The formation of a cambial ring (vascular cambium) and its sustained divisions produce secondary xylem and secondary phloem, directly causing thickening. This is structurally evident as expanding wood and bark regions and can be tracked over time by increasing girth and internal layering. Leaf initiation at the shoot tip reflects apical meristem activity, while root hairs relate to differentiation in primary tissues. Large air spaces are features of specialized parenchyma in certain organs, not direct evidence of lateral meristem function. Therefore, cambial ring formation with diameter increase most strongly indicates active lateral meristem activity.
40. A student claims: “Lateral meristems only form protective tissues, not conducting tissues.” Which statement best corrects this claim using the function of lateral meristems?
ⓐ. Lateral meristems mainly produce only parenchyma for storage, not vascular tissues
ⓑ. Lateral meristems include vascular cambium that produces secondary conducting tissues, while cork cambium produces protective tissues
ⓒ. Lateral meristems are found only at tips, so they cannot form either protective or conducting tissues
ⓓ. Lateral meristems stop functioning after the first year, so they never contribute to conduction
Correct Answer: Lateral meristems include vascular cambium that produces secondary conducting tissues, while cork cambium produces protective tissues
Explanation: The term “lateral meristem” includes more than one meristem type, and their functions are not limited to protection. Vascular cambium is a lateral meristem that produces secondary xylem and secondary phloem, which are conducting tissues essential for long-distance transport and increased capacity in thick stems and roots. Cork cambium, another lateral meristem, produces periderm components that protect older regions as they expand. Together, these meristems coordinate thickening with both enhanced transport and improved protection. This directly corrects the misconception that lateral meristems only form protective tissues. Therefore, lateral meristems include vascular cambium for secondary conducting tissues and cork cambium for protective tissues.
41. Which feature is most characteristic of parenchyma as a simple permanent tissue?
ⓐ. Cells are dead at maturity with thick lignified secondary walls
ⓑ. Cells are living but have uniformly thickened walls only at corners
ⓒ. Cells are living and arranged without intercellular spaces to resist stretching
ⓓ. Cells are living with thin cellulosic walls and usually show intercellular spaces
Correct Answer: Cells are living with thin cellulosic walls and usually show intercellular spaces
Explanation: Parenchyma consists of living cells with thin primary (cellulosic) walls and a prominent vacuole, making them well-suited for metabolism, storage, and gentle support via turgor. They are typically isodiametric or slightly elongated and are often loosely packed, creating intercellular spaces that facilitate diffusion of gases and movement of water within tissues. This basic design allows parenchyma to occur widely in cortex, pith, mesophyll, and even as living components of vascular tissues. Because the walls are not heavily thickened, these cells remain flexible and capable of physiological activity. The presence of living protoplasm and usually noticeable intercellular spaces is a reliable diagnostic combination. Hence, thin-walled living cells with intercellular spaces best characterize parenchyma.
42. A plant organ shows mild mechanical support mainly due to cell turgidity rather than thickened lignified walls. Which tissue most directly provides such support?
ⓐ. Parenchyma
ⓑ. Sclerenchyma fibres
ⓒ. Tracheary elements of xylem
ⓓ. Cork (phellem)
Correct Answer: Parenchyma
Explanation: Parenchyma cells have large vacuoles and living cytoplasm, so when they are fully turgid, internal pressure presses against their thin walls and provides firmness to soft plant parts. This “turgor-based” support is especially important in young stems, leaves, and non-woody organs where flexibility is needed along with stability. Unlike sclerenchyma and xylem elements, parenchyma does not rely on thick, lignified secondary walls for strength. The supportive effect depends on water status, which is why wilting reduces rigidity in herbaceous plants. This mechanism is a classic application of parenchyma structure to function. Therefore, parenchyma most directly provides turgor-based mechanical support.
43. Which modified form of parenchyma is primarily specialized for photosynthesis?
ⓐ. Aerenchyma
ⓑ. Storage parenchyma
ⓒ. Chlorenchyma
ⓓ. Xylem parenchyma
Correct Answer: Chlorenchyma
Explanation: Chlorenchyma is parenchyma that contains abundant chloroplasts, making it specialized for photosynthesis in green parts of the plant. It commonly forms leaf mesophyll (palisade and spongy tissues) and may also occur in young green stems. The thin walls and living protoplasm allow efficient light capture, CO₂ diffusion, and biochemical activity needed for sugar synthesis. Because parenchyma can differentiate into functionally specialized types, chlorenchyma represents a direct link between tissue anatomy and the photosynthetic role of leaves. Its defining feature is the presence of chloroplast-rich living cells rather than storage dominance or large air cavities. Hence, chlorenchyma is the parenchyma type primarily adapted for photosynthesis.
44. In aquatic plants, large air-filled cavities that aid buoyancy and internal gas diffusion are mainly due to:
ⓐ. Sclerenchyma fibres arranged in bundles
ⓑ. Aerenchyma formation within parenchyma
ⓒ. Collenchyma thickening at cell corners
ⓓ. Secondary growth producing spongy wood
Correct Answer: Aerenchyma formation within parenchyma
Explanation: Aerenchyma is a specialized parenchyma characterized by very large intercellular spaces or air chambers that store and conduct gases. In aquatic and waterlogged conditions, this anatomical feature helps supply oxygen to submerged tissues and facilitates exchange of respiratory gases throughout the plant body. The air spaces also contribute to buoyancy, helping leaves and stems remain positioned for light capture. Because parenchyma cells can separate or undergo controlled cell death to create cavities, the tissue remains fundamentally parenchymatous in origin. This adaptation is not produced by mechanical tissues like sclerenchyma or by secondary growth patterns. Therefore, aerenchyma within parenchyma is responsible for large air cavities aiding buoyancy and gas diffusion.
45. A cut potato develops new tissue that helps seal an injured surface over time. Which parenchyma-related property best explains this repair?
ⓐ. Parenchyma cells are naturally lignified and become wood to close wounds
ⓑ. Parenchyma cells are dead and act as a permanent barrier immediately after cutting
ⓒ. Parenchyma cells can only transport water, so they flood the wound region
ⓓ. Living parenchyma can resume division and form wound-healing tissue (callus-like growth)
Correct Answer: Living parenchyma can resume division and form wound-healing tissue (callus-like growth)
Explanation: Parenchyma cells remain living and relatively unspecialized compared to many other tissues, so they can regain meristematic activity under appropriate conditions. After injury, cells near the cut surface may divide and produce new cells that help cover and protect exposed tissue, reducing infection and water loss. This regenerative potential is closely tied to the living protoplasm and flexible primary walls of parenchyma, which allow re-entry into the cell cycle and subsequent differentiation. Such repair is a key physiological advantage in storage organs like tubers. The process is not immediate wood formation, nor does it depend on dead cells. Hence, wound healing is explained by the ability of living parenchyma to divide and form protective new tissue.
46. Which statement best describes storage parenchyma in many plant organs?
ⓐ. It commonly stores starch, oils, or proteins in living thin-walled cells
ⓑ. It transports sugars through sieve tubes using perforated end walls
ⓒ. It provides rigid support through thick lignified secondary walls
ⓓ. It forms the outermost waterproof covering by producing suberized layers
Correct Answer: It commonly stores starch, oils, or proteins in living thin-walled cells
Explanation: Storage parenchyma is made of living, thin-walled cells adapted to accumulate reserve materials such as starch (in tubers), oils (in many seeds), or proteins (in cotyledons and endosperm-rich seeds). Large vacuoles and specialized plastids support this storage function, allowing the plant to mobilize reserves during germination, regrowth, or stress. Because the cells remain alive, they can actively convert and transport stored materials when needed. This role is fundamentally different from conduction via sieve tubes and from rigid support provided by heavily lignified tissues. Storage parenchyma is therefore a key metabolic and reserve-maintenance tissue across many organs. Hence, it is correctly described as living thin-walled cells storing starch, oils, or proteins.
47. Xylem parenchyma is best associated with which function within the vascular system?
ⓐ. Long-distance conduction of water through hollow dead cells only
ⓑ. Loading and unloading of sugars into sieve tubes under pressure flow
ⓒ. Storage of food and lateral transport of water and solutes within xylem
ⓓ. Formation of a waterproof barrier to replace epidermis in old stems
Correct Answer: Storage of food and lateral transport of water and solutes within xylem
Explanation: Xylem parenchyma is the living component of xylem and plays key roles that complement the conducting elements. It commonly stores starch and other reserves and participates in lateral (radial) movement of water, minerals, and dissolved substances across the xylem, helping distribute resources to adjacent tissues. Because it is living, it can also contribute to repair processes such as blocking injured vessels and supporting functional maintenance in older xylem regions. This contrasts with vessels and tracheids, which mainly conduct water and provide support but are typically dead at maturity. Sugar loading is a phloem-associated process, not a primary xylem parenchyma role. Therefore, storage and lateral transport within xylem best describes xylem parenchyma function.
48. A student says: “Parenchyma is always tightly packed with no gaps, so gases cannot move through it.” Which statement corrects this misconception?
ⓐ. Parenchyma has thick lignified walls, so gases diffuse only through pits
ⓑ. Parenchyma is replaced by sclerenchyma in leaves, so diffusion happens elsewhere
ⓒ. Parenchyma cells are dead, so gas diffusion is irrelevant in plant tissues
ⓓ. Parenchyma often has intercellular spaces that facilitate diffusion, especially in leaf mesophyll
Correct Answer: Parenchyma often has intercellular spaces that facilitate diffusion, especially in leaf mesophyll
Explanation: In many organs, parenchyma cells are loosely arranged, and the resulting intercellular spaces create a continuous internal pathway for gas movement. This is especially important in leaf spongy mesophyll, where large spaces allow CO₂ to diffuse efficiently to photosynthetic cells and permit O₂ to move out. Because parenchyma is living and thin-walled, diffusion across cell surfaces and through air spaces is effective and supports metabolism. While some parenchyma may be compact in certain regions, it is not correct to generalize that parenchyma has no gaps. The structural variability of parenchyma is a key reason it serves diverse functions. Hence, intercellular spaces in parenchyma often facilitate diffusion, particularly in leaf mesophyll.
49. Which option best identifies a common anatomical location where parenchyma forms a major portion of ground tissue?
ⓐ. Only inside xylem vessels as hollow tubes
ⓑ. Cortex and pith regions of stems and roots
ⓒ. Only in the epidermal layer as protective cells
ⓓ. Only in phloem fibres as supporting strands
Correct Answer: Cortex and pith regions of stems and roots
Explanation: Ground tissue in many plant organs is largely composed of parenchyma, particularly in the cortex (between epidermis and vascular tissues) and the pith (central region in many stems). In these regions, parenchyma performs multiple roles including storage, internal transport, and support by turgor, depending on the organ and developmental stage. The cells remain living and metabolically active, which is consistent with functions like reserve accumulation and tissue maintenance. Xylem vessels are specialized conducting elements, not the primary ground tissue matrix, and epidermis is a protective tissue system. Phloem fibres are supportive and do not represent the bulk ground tissue. Therefore, cortex and pith are common locations where parenchyma constitutes most of the ground tissue.
50. A leaf tissue shows elongated cells arranged in columns with many chloroplasts, maximizing light absorption. This tissue is best described as:
ⓐ. Palisade parenchyma (a chlorenchyma type)
ⓑ. Collenchyma located beneath epidermis for flexible support
ⓒ. Sclerenchyma fibres surrounding vascular bundles for rigidity
ⓓ. Aerenchyma with large air chambers for buoyancy
Correct Answer: Palisade parenchyma (a chlorenchyma type)
Explanation: Palisade parenchyma consists of elongated, closely arranged cells rich in chloroplasts, typically located beneath the upper epidermis of many leaves. This arrangement increases light interception and supports high photosynthetic efficiency by concentrating chloroplast-bearing cells where light intensity is greatest. Being a form of chlorenchyma, it shares parenchyma’s living, thin-walled nature while specializing for photosynthesis rather than storage or mechanical strength. The columnar structure also reduces shading between cells and promotes effective CO₂ diffusion within the leaf. Collenchyma and sclerenchyma are primarily mechanical tissues, and aerenchyma is characterized by large air spaces. Hence, the described tissue is palisade parenchyma, a photosynthetic parenchyma type.
51. Which statement best defines collenchyma as a simple permanent tissue?
ⓐ. Living cells with unevenly thickened primary walls that provide flexible support
ⓑ. Dead cells with uniformly lignified secondary walls that provide rigid strength
ⓒ. Living cells with large air cavities that improve buoyancy and gas diffusion
ⓓ. Dead conducting cells with perforations that mainly transport water upward
Correct Answer: Living cells with unevenly thickened primary walls that provide flexible support
Explanation: Collenchyma is a living mechanical tissue designed to support growing organs without restricting their expansion. Its cells have unevenly thickened primary walls, typically due to cellulose and pectin, which gives strength while retaining flexibility. Because the walls are not heavily lignified, the tissue can bend and stretch as stems and leaves grow. Collenchyma commonly occurs in young stems, petioles, and leaf midribs where mechanical reinforcement is needed during active growth. The cells remain metabolically active, supporting repair and continued development. Therefore, collenchyma is best defined by living cells with uneven primary wall thickening that provides flexible support.
52. Which location is most typical for collenchyma in a young dicot stem?
ⓐ. Around the endodermis as a ring of compact storage cells
ⓑ. Just below the epidermis in the hypodermal region
ⓒ. Inside the vascular bundles as the main water-conducting tissue
ⓓ. At the center of the pith as large vacuolated storage cells
Correct Answer: Just below the epidermis in the hypodermal region
Explanation: In young dicot stems, collenchyma is commonly positioned beneath the epidermis as part of the hypodermis. This placement provides early mechanical support to the outer stem, which experiences bending forces from wind and the weight of leaves. Being close to the surface makes it effective at resisting tensile stress while still allowing the stem to elongate. The tissue remains living, so it supports growing regions rather than only mature, rigid structures. Vascular bundles contain xylem and phloem elements, not collenchyma as the main conductor. Hence, the typical location is just below the epidermis in the hypodermal region.
53. The wall thickening in collenchyma is primarily due to deposition of:
ⓐ. Suberin and cutin, making the walls waterproof
ⓑ. Lignin, making the cells rigid and dead at maturity
ⓒ. Cellulose and pectin in the primary wall, increasing strength with flexibility
ⓓ. Silica crystals that harden the cell corners permanently
Correct Answer: Cellulose and pectin in the primary wall, increasing strength with flexibility
Explanation: Collenchyma walls are thickened as part of the primary wall and are rich in cellulose and pectin. This composition strengthens the tissue while preserving elasticity, enabling support in organs that are still growing. Because lignin deposition is minimal or absent, collenchyma does not become rigid like sclerenchyma and typically remains living. Pectin also contributes to wall plasticity and helps the tissue withstand stretching during growth. This biochemical basis directly explains why collenchyma supports without preventing elongation. Therefore, cellulose and pectin deposition in primary walls is the key cause of collenchyma thickening.
54. Which type of collenchyma is identified by thickening mainly at the corners (angles) of cells?
ⓐ. Lacunar collenchyma
ⓑ. Lamellar collenchyma
ⓒ. Septate collenchyma
ⓓ. Angular collenchyma
Correct Answer: Angular collenchyma
Explanation: Angular collenchyma shows characteristic wall thickening at the cell corners where adjacent cells meet. This corner-focused reinforcement increases mechanical strength while maintaining a living, flexible tissue framework. It is commonly observed in the hypodermis of young stems and petioles, where tissues must resist bending and tensile forces. Because thickening is uneven, the cells can still expand and accommodate growth. The diagnostic feature is the “angular” appearance created by reinforced corners in transverse section. Hence, collenchyma with corner thickening is correctly identified as angular collenchyma.
55. A student bends a young petiole repeatedly, and it springs back without cracking. Which tissue most directly explains this flexible mechanical support?
ⓐ. Collenchyma concentrated in the petiole and leaf midrib
ⓑ. Sclerenchyma fibres with heavily lignified secondary walls
ⓒ. Cork tissue forming a protective, impermeable layer
ⓓ. Xylem vessels acting as the main elastic elements
Correct Answer: Collenchyma concentrated in the petiole and leaf midrib
Explanation: Flexible support in growing leaf parts such as petioles is a hallmark function of collenchyma. Its living cells have unevenly thickened primary walls that provide tensile strength while still allowing bending and recovery. Because the tissue is not strongly lignified, it can deform under stress and then regain shape, helping young organs withstand mechanical strain. This is especially important in petioles and midribs that experience frequent movement due to wind. Sclerenchyma provides rigid support and is more likely to resist bending but not “springy” flexibility in young parts. Therefore, collenchyma best explains the petiole’s flexible mechanical support.
56. Which statement best distinguishes collenchyma from sclerenchyma in terms of functional outcome in growing organs?
ⓐ. Collenchyma prevents all bending, while sclerenchyma allows stretching during growth
ⓑ. Collenchyma conducts water, while sclerenchyma conducts sugars
ⓒ. Collenchyma supports growing parts with flexibility, while sclerenchyma provides rigid strength mainly in mature parts
ⓓ. Collenchyma forms protective periderm, while sclerenchyma forms epidermis
Correct Answer: Collenchyma supports growing parts with flexibility, while sclerenchyma provides rigid strength mainly in mature parts
Explanation: Collenchyma is adapted to support organs that are still elongating, so its walls are thickened but remain primary and non-rigid enough to permit flexibility. In contrast, sclerenchyma develops thick, lignified secondary walls and is commonly dead at maturity, making it ideal for rigid mechanical support in fully developed parts. This difference produces distinct functional outcomes: collenchyma resists tearing while allowing bending, whereas sclerenchyma strongly resists deformation but can restrict growth. The living nature of collenchyma also suits it to young tissues that must remain physiologically active. Hence, collenchyma supports with flexibility during growth, while sclerenchyma provides rigid strength mainly in mature regions.
57. Lamellar (tangential) collenchyma is best identified by wall thickening that is mainly:
ⓐ. At the cell corners, producing an angular appearance
ⓑ. On the tangential walls, forming layers parallel to the organ surface
ⓒ. Uniform all around the cell, giving equal thickness on every side
ⓓ. Only at pits, leaving most wall regions thin and unreinforced
Correct Answer: On the tangential walls, forming layers parallel to the organ surface
Explanation: In lamellar collenchyma, wall thickening occurs predominantly on the tangential walls, which run parallel to the surface of the organ. This creates a layered reinforcement pattern that is especially effective in resisting bending forces acting across the outer regions of stems and petioles. The arrangement supports the organ while still allowing extension growth, because the tissue remains living and primary-wall based. The “lamellar” name reflects these parallel layers of thickening. This pattern differs from angular collenchyma, where corners are the main thickened regions. Therefore, lamellar collenchyma is identified by thickening on tangential walls in layers parallel to the surface.
58. Which feature is most likely to be observed in collenchyma cells under a microscope?
ⓐ. Living protoplasm with no lignification and uneven primary wall thickening
ⓑ. Hollow dead tubes with perforated end walls and thick lignified walls
ⓒ. Completely suberized walls forming an impermeable protective barrier
ⓓ. Thick secondary walls with wide lumen and numerous bordered pits only
Correct Answer: Living protoplasm with no lignification and uneven primary wall thickening
Explanation: Collenchyma cells retain living contents, so a microscope view typically reveals protoplasm and an active cellular organization. Their defining structural feature is uneven thickening of the primary wall, usually without strong lignification, which keeps the tissue flexible. This matches their role in supporting young organs that must continue expanding. Because the walls remain primarily cellulosic and pectin-rich, the tissue does not show the rigid, heavily lignified appearance typical of sclerenchyma. Nor does it resemble the hollow conducting elements of xylem. Hence, living protoplasm with uneven primary wall thickening and minimal lignification is the characteristic microscopic feature of collenchyma.
59. Lacunar collenchyma is most correctly associated with:
ⓐ. Completely compact cells with no intercellular spaces anywhere
ⓑ. Air cavities formed by cell death, leaving only dead supporting tissue
ⓒ. Uniform thickening of all walls to produce rigid mechanical strength
ⓓ. Thickening around intercellular spaces, often seen near leaf veins or petioles
Correct Answer: Thickening around intercellular spaces, often seen near leaf veins or petioles
Explanation: Lacunar collenchyma is characterized by wall thickening that is prominent around the margins of intercellular spaces (lacunae). This arrangement strengthens regions where spaces could otherwise reduce mechanical integrity, while still allowing some internal diffusion and flexibility. It is often observed in parts like petioles and leaf regions where support is needed along with tissue lightness and adaptability. The tissue remains living and primary-wall based, so it continues to function during growth. The key diagnostic point is reinforcement around spaces rather than exclusively at corners or in uniform layers. Therefore, lacunar collenchyma is correctly linked to thickening around intercellular spaces.
60. Which statement most accurately describes why collenchyma is commonly absent or less developed in mature, woody stems?
ⓐ. Woody stems rely more on rigid, lignified supporting tissues, reducing the need for flexible collenchyma
ⓑ. Woody stems have no mechanical stress, so supportive tissues are unnecessary
ⓒ. Woody stems cannot form any living tissues, so collenchyma cannot exist there
ⓓ. Woody stems use only epidermis for support, not internal tissues
Correct Answer: Woody stems rely more on rigid, lignified supporting tissues, reducing the need for flexible collenchyma
Explanation: As stems mature and become woody, mechanical support increasingly depends on rigid, lignified tissues, especially secondary xylem and associated fibres. These tissues provide strong resistance to bending and compression for long-term structural stability. Collenchyma is most beneficial in young, actively growing regions where flexibility and extensibility are required, but these needs diminish as secondary growth establishes a strong woody framework. Also, outer tissues in older stems are often replaced by protective coverings, and support shifts inward to wood. Collenchyma can still occur in some parts, but it is typically less prominent compared to early stages. Therefore, mature woody stems rely on rigid lignified support, reducing the functional demand for flexible collenchyma.
61. Which statement best describes the cell wall thickening style in sclerenchyma cells?
ⓐ. Thick, lignified secondary walls deposited evenly to provide high mechanical strength
ⓑ. Thin primary walls with pectin-rich corner thickening for flexible support
ⓒ. Suberin-rich walls forming a waterproof barrier in outer protective tissues
ⓓ. Cell walls remain thin and are strengthened mainly by turgor pressure
Correct Answer: Thick, lignified secondary walls deposited evenly to provide high mechanical strength
Explanation: Sclerenchyma cells characteristically develop very thick secondary walls that are heavily lignified, making the tissue strong and rigid. The secondary wall is laid down after cell expansion, so these cells usually become non-elongating and often lose protoplasm at maturity. Lignin impregnation increases hardness and resistance to compression and bending. This wall thickening is typically more uniform around the cell, unlike the uneven primary-wall thickening seen in flexible supporting tissues. Small pits remain for limited exchange during development, but the dominant feature is massive lignified secondary thickening. Hence, thick, lignified secondary walls are the defining thickening style of sclerenchyma.
62. A student observes thick secondary walls with numerous pits in elongated supporting cells near vascular bundles. These cells are best identified as:
ⓐ. Collenchyma cells
ⓑ. Sclerenchyma fibres
ⓒ. Parenchyma cells
ⓓ. Guard cells
Correct Answer: Sclerenchyma fibres
Explanation: Sclerenchyma fibres are elongated, tapering cells specialized for mechanical support and commonly occur around vascular bundles as strengthening caps. Their thick, lignified secondary walls provide high tensile strength, and pits are present as small regions where secondary wall deposition is reduced. These pits help maintain some connectivity during development, though mature fibres are typically dead. The combination of elongation, heavy lignification, and pit presence aligns strongly with fibres rather than living thin-walled parenchyma or unevenly thickened collenchyma. Guard cells are epidermal structures and have a different morphology and function. Therefore, the described cells are sclerenchyma fibres.
63. Which feature best distinguishes sclereids from sclerenchyma fibres with respect to thickening pattern and form?
ⓐ. Sclereids have suberized walls and form the main waterproof barrier
ⓑ. Sclereids are long and thread-like with thin primary walls and living contents
ⓒ. Sclereids lack secondary walls and are strengthened only by turgor
ⓓ. Sclereids are short/irregular with very thick lignified walls and a narrow lumen
Correct Answer: Sclereids are short/irregular with very thick lignified walls and a narrow lumen
Explanation: Sclereids are a sclerenchyma type that are typically shorter and irregular in shape compared to long, slender fibres. They develop extremely thick, lignified secondary walls that greatly reduce the lumen, producing a gritty or hard texture in certain plant parts. The thickening is massive and often appears more “block-like” due to the cell’s shape, with pits present as channels across the wall. Their primary role is mechanical protection and hardness rather than tensile support over long distances. This contrasts with fibres, which are elongated and mainly resist pulling forces. Hence, short/irregular cells with very thick lignified walls and narrow lumen best describe sclereids.
64. In sclerenchyma, pits are best understood as:
ⓐ. Regions where secondary wall deposition is reduced, allowing limited exchange pathways through the wall
ⓑ. Open holes created after the entire cell wall dissolves during maturation
ⓒ. Areas of corner thickening made of cellulose and pectin for flexibility
ⓓ. Suberin plugs that completely block movement across the wall
Correct Answer: Regions where secondary wall deposition is reduced, allowing limited exchange pathways through the wall
Explanation: Pits are localized areas of the cell wall where secondary wall thickening is absent or reduced, leaving the primary wall relatively exposed. In sclerenchyma, thick secondary walls dominate, but pits remain as essential structural features that preserve some continuity for communication during development. These pit regions do not represent complete perforations; rather, they are thinner wall zones that can align with pits in adjacent cells. The presence of pits is compatible with strong walls because the overall wall remains heavily lignified and supportive. The concept is fundamentally about patterned secondary wall deposition, not total wall loss. Therefore, pits are regions of reduced secondary wall thickening that permit limited exchange pathways.
65. A hard seed coat shows abundant thick-walled, isodiametric cells that contribute to hardness. Which sclerenchyma element is most likely responsible?
ⓐ. Xylem vessels
ⓑ. Collenchyma strands
ⓒ. Parenchyma with large air spaces
ⓓ. Sclereids
Correct Answer: Sclereids
Explanation: Seed coats often derive their hardness from sclereids, which are thick-walled sclerenchyma cells providing strong mechanical protection. These cells are commonly isodiametric or irregular, with very thick lignified secondary walls and a narrow lumen, making the tissue dense and hard. Their arrangement forms a protective barrier against mechanical injury and predation, enhancing seed survival. While xylem vessels conduct water and are not the typical cause of seed coat hardness, collenchyma is flexible and usually found in growing organs. Parenchyma with air spaces is linked to diffusion and buoyancy rather than hardness. Hence, sclereids are the most likely sclerenchyma element responsible for a hard seed coat.
66. Which wall component is most directly responsible for the rigidity of sclerenchyma secondary walls?
ⓐ. Lignin deposition in the secondary wall matrix
ⓑ. High pectin content limited to the middle lamella only
ⓒ. Cutin layers laid over the epidermal surface
ⓓ. Protein filaments that replace cellulose microfibrils
Correct Answer: Lignin deposition in the secondary wall matrix
Explanation: The hallmark stiffness of sclerenchyma arises from lignin impregnation of the secondary wall, which strengthens and waterproofs the wall to a degree and greatly increases resistance to compression. Lignin binds within the wall matrix around cellulose microfibrils, producing a hard, durable structure suited for long-term support and protection. This chemical reinforcement is why sclerenchyma tissues are tough and often dead at maturity. Pectin-rich walls are typical of flexible primary-wall tissues rather than rigid secondary-wall tissues. Cutin is a surface protective polymer of epidermal coverings, not the main cause of sclerenchyma rigidity. Therefore, lignin deposition in the secondary wall is the key contributor to sclerenchyma rigidity.
67. Which statement best explains why sclerenchyma thickening typically occurs after cell elongation is largely complete?
ⓐ. Heavy lignified secondary walls restrict further expansion, so thickening is deposited after growth in size
ⓑ. Thickening happens first to allow rapid elongation under high tensile stress
ⓒ. Secondary walls are always thin and flexible, so elongation continues indefinitely
ⓓ. Thickening occurs only at the cell corners to permit uniform stretching
Correct Answer: Heavy lignified secondary walls restrict further expansion, so thickening is deposited after growth in size
Explanation: Sclerenchyma cells are designed for strength, and their thick lignified secondary walls would mechanically hinder cell stretching if deposited too early. Therefore, the cell typically enlarges and reaches near-final dimensions first, and only then does it deposit extensive secondary wall layers. This sequence preserves the ability to grow in size while ensuring that the mature cell becomes highly supportive. Once secondary thickening is complete, the lumen narrows, the wall becomes rigid, and the cell often loses living contents. This developmental timing aligns structure with function: first reach size, then reinforce for strength. Hence, sclerenchyma thickening occurs after elongation because lignified secondary walls restrict further expansion.
68. “Gritty” texture in the pulp of certain fruits is mainly due to which sclerenchyma thickening-related feature?
ⓐ. Presence of sclereids with extremely thick lignified secondary walls
ⓑ. Presence of collenchyma with uneven pectin thickening at corners
ⓒ. Presence of aerenchyma with large air chambers in parenchyma
ⓓ. Presence of cork cells with suberin lamellae
Correct Answer: Presence of sclereids with extremely thick lignified secondary walls
Explanation: The gritty feel in some fruit pulps is classically linked to sclereids, which are thick-walled sclerenchyma cells embedded within softer tissues. Their very thick lignified secondary walls and small lumen make them hard particles relative to surrounding parenchyma. Because sclereids are irregular and densely walled, they resist crushing and can be felt during chewing. This is a direct outcome of sclerenchyma wall thickening style—massive lignified secondary deposition. Collenchyma is flexible and does not create grit, and aerenchyma creates air spaces rather than hardness. Therefore, gritty texture is mainly due to sclereids with extremely thick lignified secondary walls.
69. Which thickening pattern is most typical of sclerenchyma fibres in terms of mechanical role?
ⓐ. Extremely uneven corner thickening to allow stretching during growth
ⓑ. Thin walls with wide lumen to maximize storage and diffusion
ⓒ. Uniform, massive secondary wall thickening along the length to resist tensile forces
ⓓ. Suberized outer layers forming a waterproof covering over the stem
Correct Answer: Uniform, massive secondary wall thickening along the length to resist tensile forces
Explanation: Sclerenchyma fibres function primarily to resist pulling (tensile) forces, so their walls are thickened strongly and extensively along the length of the cell. The secondary wall is heavily lignified and relatively uniform, providing a high strength-to-length support system that reinforces bundles and protective caps. This uniformity ensures consistent mechanical performance along the fibre, allowing it to act like a tough reinforcing strand within tissues. Corner thickening is a feature of flexible support tissues, not rigid fibres. Thin walls with wide lumen would favor storage, not strength. Hence, fibres typically show uniform, massive secondary wall thickening to resist tensile stress.
70. A student finds thick-walled dead cells that occur as long strands in vascular bundle caps and also as isolated hard cells in seed coats. Which option correctly matches these two sclerenchyma forms?
ⓐ. Long strands = sclereids; isolated hard cells = fibres
ⓑ. Long strands = fibres; isolated hard cells = sclereids
ⓒ. Long strands = parenchyma; isolated hard cells = collenchyma
ⓓ. Long strands = cork cells; isolated hard cells = vessels
Correct Answer: Long strands = fibres; isolated hard cells = sclereids
Explanation: Sclerenchyma occurs mainly as fibres and sclereids, both with thick lignified secondary walls and typically dead at maturity. Fibres are elongated and occur in bundles or caps around vascular tissues, where they provide tensile reinforcement and strengthen the organ. Sclereids are shorter and more irregular, often scattered as hard “stone cells” in seed coats and other tissues where protection and hardness are needed. The difference in form is closely tied to functional placement: strands for reinforcement versus isolated cells for hardness. This matching aligns with standard anatomical identification. Therefore, long strands are fibres and isolated hard cells in seed coats are sclereids.
71. Which xylem element is most characteristic of flowering plants and is specialized for rapid water conduction through end-to-end perforations?
ⓐ. Tracheid
ⓑ. Xylem parenchyma
ⓒ. Xylem fibre
ⓓ. Vessel element
Correct Answer: Vessel element
Explanation: Vessel elements are a major conducting component of xylem in flowering plants and are arranged end-to-end to form continuous vessels. Their end walls develop perforation plates, which reduce resistance to flow compared to closed end walls, enabling more efficient water transport. The walls are thick and lignified, providing mechanical support alongside conduction. Because they are dead at maturity, the lumen remains open for water movement under tension. This specialization makes vessels a key reason many flowering plants can move water efficiently through tall stems. Therefore, vessel elements are the characteristic xylem cells enabling rapid conduction via perforations.
72. In phloem tissue of flowering plants, which cell type provides metabolic support to sieve tube elements and is closely connected through numerous cytoplasmic strands?
ⓐ. Phloem fibre
ⓑ. Companion cell
ⓒ. Xylem parenchyma
ⓓ. Tracheid
Correct Answer: Companion cell
Explanation: Companion cells are living phloem cells that remain intimately associated with sieve tube elements and are connected to them by many plasmodesmata. Sieve tube elements have reduced internal machinery at maturity, so companion cells help manage metabolic functions and facilitate loading/unloading of sugars. This partnership supports pressure-driven translocation of organic solutes through the phloem pathway. Companion cells also contribute to maintaining membrane transport processes required for efficient long-distance movement. Their close structural association is a hallmark of flowering plant phloem organization. Hence, companion cells provide essential metabolic support to sieve tube elements.
73. Which component of xylem is primarily responsible for mechanical strength rather than long-distance water conduction?
ⓐ. Xylem fibres
ⓑ. Vessel elements
ⓒ. Tracheids
ⓓ. Xylem parenchyma
Correct Answer: Xylem fibres
Explanation: Xylem fibres are sclerenchymatous, thick-walled cells within xylem that mainly provide mechanical support to stems and other organs. Their heavily lignified secondary walls contribute tensile strength and help the plant resist bending and breakage. While vessels and tracheids are the main water-conducting elements, fibres are more specialized for strengthening the vascular framework. Because fibres often have a very narrow lumen, they are not optimized for bulk water flow. Their distribution around conducting elements reinforces xylem tissue during secondary growth and in mature organs. Therefore, xylem fibres primarily contribute mechanical strength.
74. Sieve tube elements are best described as:
ⓐ. Dead, lignified cells with perforation plates for rapid water flow
ⓑ. Living cells with thick secondary walls and numerous bordered pits
ⓒ. Living conducting cells with sieve plates that transport sugars under pressure flow
ⓓ. Non-living cells that store starch and assist in lateral transport
Correct Answer: Living conducting cells with sieve plates that transport sugars under pressure flow
Explanation: Sieve tube elements are the chief conducting cells of phloem in flowering plants and transport sugars and other organic solutes through sieve plates. They remain living but show reduced cell contents at maturity, which helps lower resistance for translocation. Movement in phloem is commonly explained by pressure-flow: solutes are loaded, water follows osmotically, and a pressure gradient drives mass flow. Sieve plates, with multiple pores, allow continuity of the translocation stream between adjacent elements. Their function is therefore long-distance food transport rather than water conduction or storage dominance. Hence, sieve tube elements are living conducting cells with sieve plates for sugar transport.
75. If a stem region’s phloem is removed in a ring (girdling), which immediate transport effect is most expected?
ⓐ. Upward water transport stops first because xylem is interrupted
ⓑ. Mineral uptake by root hairs ceases because epidermis is removed
ⓒ. Photosynthesis stops immediately because chloroplasts are destroyed
ⓓ. Downward movement of sugars is disrupted, leading to accumulation above the cut
Correct Answer: Downward movement of sugars is disrupted, leading to accumulation above the cut
Explanation: Girdling removes or damages phloem, which is responsible for translocating sugars and other organic solutes from sources (like leaves) to sinks (like roots, fruits, and growing tissues). When phloem is interrupted, sugars accumulate above the girdle because they cannot be transported downward effectively. Xylem, typically deeper, may continue to conduct water upward for some time, so wilting is not the first immediate effect. The key physiological consequence is disruption of food supply to tissues below the cut, including roots. This scenario is often used to demonstrate phloem’s role in translocation. Therefore, girdling disrupts downward sugar movement and causes accumulation above the removed ring.
76. Which pair correctly matches a complex tissue with its primary transported material?
ⓐ. Xylem → water and minerals; Phloem → organic solutes like sucrose
ⓑ. Xylem → sucrose; Phloem → water under tension
ⓒ. Xylem → hormones only; Phloem → minerals only
ⓓ. Xylem → amino acids only; Phloem → lignin precursors only
Correct Answer: Xylem → water and minerals; Phloem → organic solutes like sucrose
Explanation: Xylem primarily transports water and dissolved minerals from roots toward aerial parts, largely through dead conducting elements that form continuous pathways. Phloem mainly transports organic solutes, especially sucrose, along with other signaling molecules, from sources to sinks via living conducting elements. This division of labor is central to plant vascular organization and supports both hydration/mineral nutrition and distribution of photosynthates. While both tissues can carry additional substances, their primary transported materials remain distinct and are commonly tested. The mechanisms also differ, with xylem driven mainly by transpiration-related tension and phloem driven by pressure gradients. Hence, xylem carries water/minerals and phloem carries organic solutes like sucrose.
77. Which phloem element is most directly associated with mechanical support and often occurs as thick-walled strands?
ⓐ. Sieve tube element
ⓑ. Phloem fibre
ⓒ. Companion cell
ⓓ. Phloem parenchyma
Correct Answer: Phloem fibre
Explanation: Phloem fibres are sclerenchymatous cells associated with phloem that provide mechanical strength to vascular regions. They typically develop thick, lignified walls and often become dead at maturity, making them effective reinforcing strands. Their role is supportive rather than conductive, helping protect delicate conducting cells from compressive and bending forces. Because they may form caps around vascular bundles, they contribute significantly to tissue toughness. In contrast, sieve tubes and companion cells are mainly involved in transport, while phloem parenchyma is living and often storage-related. Therefore, phloem fibres are the phloem elements most directly linked to mechanical support.
78. Which xylem element can conduct water and also provide support, and is common in both flowering plants and non-flowering vascular plants?
ⓐ. Vessel element
ⓑ. Xylem fibre
ⓒ. Tracheid
ⓓ. Sieve tube element
Correct Answer: Tracheid
Explanation: Tracheids are elongated xylem cells with lignified walls that conduct water through pits rather than perforation plates. They are widespread across vascular plants and are present in both flowering plants and non-flowering groups, making them a broadly conserved conducting element. Their tapered shape and thick walls also contribute to mechanical support, especially where vessels are absent or less dominant. Water moves from one tracheid to the next through pit membranes, which maintains continuity while reducing the risk of catastrophic flow failures. This dual role of conduction and support explains their importance in plant vascular design. Hence, tracheids are common xylem elements that conduct water and provide support across major plant groups.
79. Which statement best explains why xylem conducting elements are typically dead at maturity?
ⓐ. Death allows active pumping of water using ATP along the xylem pathway
ⓑ. Death prevents lignin formation, keeping walls thin for faster diffusion
ⓒ. Death increases sugar transport efficiency through sieve plate pores
ⓓ. Loss of protoplasm creates a hollow, low-resistance pathway for water movement
Correct Answer: Loss of protoplasm creates a hollow, low-resistance pathway for water movement
Explanation: Xylem conducting elements such as vessel elements and tracheids are specialized to move large volumes of water, so an unobstructed lumen is advantageous. When these cells lose their protoplasm at maturity, the interior becomes an open conduit that reduces resistance to water flow. Thick lignified walls maintain structural integrity so the conduits do not collapse under tension created during transpiration. This design supports long-distance transport without requiring living cytoplasm inside the main pipeline. The transport is largely physical (driven by pressure/tension gradients) rather than active pumping by the conducting cells. Therefore, xylem elements are dead at maturity to form hollow, efficient water-conducting pathways.
80. Phloem parenchyma is most appropriately linked to which function within phloem tissue?
ⓐ. Storage of materials and assistance in lateral transport within the phloem region
ⓑ. Formation of perforation plates for rapid upward water conduction
ⓒ. Creating the main pressure gradient by acting as sieve plates
ⓓ. Providing the only mechanical strength by being dead and heavily lignified
Correct Answer: Storage of materials and assistance in lateral transport within the phloem region
Explanation: Phloem parenchyma consists of living cells associated with phloem that commonly store substances such as starch, oils, or other metabolites depending on the organ. These cells can also aid in short-distance (lateral) movement of solutes between phloem elements and surrounding tissues, supporting distribution and loading/unloading processes. Because they remain living, they contribute to metabolic activities and tissue maintenance around the conducting pathway. They are not the principal long-distance conducting cells, which are sieve tube elements (with companion cells). Perforation plates belong to xylem vessels, and heavy lignification is typical of fibres, not parenchyma. Hence, phloem parenchyma is best linked to storage and lateral transport support within the phloem region.
81. Which structure in sieve tube elements most directly enables mass flow of phloem sap from one element to the next?
ⓐ. Bordered pits on thick lignified walls
ⓑ. Perforation plates at the ends of dead vessels
ⓒ. Sieve plates with pores in the end walls
ⓓ. Casparian strips in the radial walls
Correct Answer: Sieve plates with pores in the end walls
Explanation: Sieve tube elements are arranged end-to-end, and their end walls develop sieve plates containing many pores that connect adjacent elements. These pores allow phloem sap (rich in sugars and other solutes) to pass with minimal resistance as part of pressure-driven mass flow. Because sieve tube elements remain living but streamlined for conduction, sieve plates are the key anatomical feature ensuring continuity of the translocation pathway. Bordered pits and perforation plates are associated with xylem conduction, not phloem translocation. Casparian strips occur in roots and regulate apoplastic movement, not sieve tube connectivity. Hence, sieve plates with pores are the direct structural basis for phloem sap flow between sieve tube elements.
82. Which xylem element is most directly involved in lateral movement of water and solutes by storage and radial transport within xylem tissue?
ⓐ. Xylem parenchyma
ⓑ. Vessel element
ⓒ. Tracheid
ⓓ. Xylem fibre
Correct Answer: Xylem parenchyma
Explanation: Xylem parenchyma is the living component of xylem and plays a major role in storage and lateral (radial) transport of substances within the xylem region. It can store starch and other reserves and help redistribute water, minerals, and dissolved solutes sideways from the main conducting elements to adjacent tissues. This complements the vertical conduction performed by vessels and tracheids. Being living, xylem parenchyma can also participate in maintenance functions such as assisting in recovery from injury by forming plugs or supporting functional continuity. Fibres mainly provide strength, and vessels/tracheids are primarily for long-distance conduction. Therefore, xylem parenchyma is most directly linked to storage and radial transport within xylem.
83. Which statement best describes the directionality of transport in xylem and phloem in a whole plant?
ⓐ. Xylem always moves downward; phloem always moves upward only
ⓑ. Xylem mainly moves upward; phloem can move in both directions depending on source–sink relations
ⓒ. Xylem and phloem both move only upward because gravity prevents downward flow
ⓓ. Xylem can move both ways freely; phloem moves only downward to roots
Correct Answer: Xylem mainly moves upward; phloem can move in both directions depending on source–sink relations
Explanation: Xylem transport is largely upward from roots to shoots because it is driven mainly by transpiration-related tension and root pressure, supplying water and minerals to aerial parts. Phloem transport, however, is governed by source–sink relationships, where sugars move from regions of production or release (sources) to regions of utilization or storage (sinks). Because sources and sinks can vary with season and organ activity, phloem can carry solutes upward or downward in different parts of the plant. This flexibility supports processes like moving sugars to roots, developing fruits, or growing shoot tips. The key distinction is that phloem direction depends on functional demand rather than being fixed. Hence, xylem is mainly upward, while phloem can be bidirectional based on source–sink dynamics.
84. Which component is essential for maintaining sieve tube function in flowering plants because sieve tube elements lack a nucleus at maturity?
ⓐ. Xylem parenchyma
ⓑ. Companion cell
ⓒ. Phloem fibre
ⓓ. Vessel element
Correct Answer: Companion cell
Explanation: Sieve tube elements in flowering plants undergo specialization that reduces their internal contents, including loss of the nucleus, to improve transport efficiency. Because they still remain living, they require nearby cells to manage metabolic processes and regulatory functions. Companion cells fulfill this role by remaining nucleated and metabolically active, and they are connected to sieve tube elements via numerous plasmodesmata. This close association enables transfer of proteins, signals, and metabolites necessary to maintain sieve tube activity and to support loading and unloading of sugars. Without companion cells, sieve tubes cannot sustain long-term functional translocation. Therefore, companion cells are essential for maintaining sieve tube function.
85. Which pairing correctly matches a vascular element with a key structural feature that supports its function?
ⓐ. Vessel element → sieve plate pores for sugar transport
ⓑ. Sieve tube element → lignified bordered pits for water conduction
ⓒ. Tracheid → pits that allow water movement between adjacent cells
ⓓ. Phloem fibre → perforation plates for rapid sap flow
Correct Answer: Tracheid → pits that allow water movement between adjacent cells
Explanation: Tracheids conduct water primarily through pits, which are regions where the secondary wall is absent or reduced, allowing water to pass from one tracheid to the next through pit membranes. This pit-based conduction is especially important where vessels are absent or less prominent, and it also supports safety against rapid spread of air embolisms. Vessel elements use perforation plates, not sieve plates, and sieve tube elements use sieve plates rather than lignified pits for their main conduction pathway. Phloem fibres are supportive sclerenchyma cells and do not form perforation plates. The correct functional-structural match is therefore tracheids with pits enabling water movement between cells. Hence, tracheid–pit pairing is correct.
86. A plant experiencing drought needs to reduce the risk of collapse of water-conducting pathways under tension. Which xylem feature most directly helps prevent conduit collapse?
ⓐ. Thin primary walls that stretch easily during water stress
ⓑ. Lignified secondary wall thickening in tracheary elements
ⓒ. Absence of pits so water cannot escape to other cells
ⓓ. Sieve plates with callose deposition to seal pores
Correct Answer: Lignified secondary wall thickening in tracheary elements
Explanation: Water in xylem is often under negative pressure (tension), especially during drought, which can create strong inward forces on conduit walls. Lignified secondary wall thickening in tracheary elements (vessels and tracheids) provides rigidity and mechanical strength so the conduits resist collapse and maintain an open lumen for conduction. This reinforcement also supports the plant structurally and allows xylem to function over long distances. Thin primary walls would be prone to deformation under tension and are typical of living parenchyma rather than tracheary elements. Sieve plates and callose are phloem-related structures and do not prevent xylem collapse. Therefore, lignified secondary wall thickening is the key xylem feature that prevents conduit collapse under tension.
87. Which phloem element is most directly involved in storage and short-distance movement of organic materials within the phloem region?
ⓐ. Sieve tube element
ⓑ. Companion cell
ⓒ. Phloem parenchyma
ⓓ. Phloem fibre
Correct Answer: Phloem parenchyma
Explanation: Phloem parenchyma consists of living cells associated with the phloem that commonly store organic substances and assist in local transport. These cells can store starch and other metabolites and facilitate lateral transfer of solutes between conducting cells and surrounding tissues, supporting efficient distribution and regulation. Unlike sieve tubes, which mainly handle long-distance transport, phloem parenchyma contributes to metabolic buffering and short-distance movement in the phloem zone. Companion cells mainly provide metabolic support specifically to sieve tube elements, while phloem fibres provide mechanical strength. The presence of living protoplasm enables phloem parenchyma to perform active physiological roles. Hence, phloem parenchyma is most directly involved in storage and short-distance solute movement within the phloem region.
88. Which statement best explains why xylem transport does not require living cytoplasm in the main conducting elements?
ⓐ. Water movement in xylem is mainly driven by physical pressure gradients and cohesion–tension, not cellular metabolism
ⓑ. Xylem sap is pumped upward by ATP-powered motors on vessel end walls
ⓒ. Water movement in xylem requires sieve plates to open and close continuously
ⓓ. Xylem transport depends on active loading of sugars into vessels to create pressure
Correct Answer: Water movement in xylem is mainly driven by physical pressure gradients and cohesion–tension, not cellular metabolism
Explanation: Xylem conduction is primarily a physical process where water moves through continuous conduits due to transpiration-driven tension, cohesion between water molecules, and adhesion to xylem walls. Because this transport relies on pressure gradients and the physical properties of water rather than active pumping by the conducting cells, the main conducting elements can be dead at maturity and still function efficiently. The absence of cytoplasm reduces resistance and creates a hollow pathway for bulk flow. ATP-powered motors and sieve plates are not part of xylem conduction, and sugar loading is a phloem mechanism. The design emphasizes low-resistance flow and structural support via lignified walls. Therefore, xylem transport does not require living cytoplasm because it is driven mainly by physical forces.
89. Which xylem element is generally longer and narrower, lacks perforation plates, and is considered safer against rapid spread of air embolism?
ⓐ. Vessel element
ⓑ. Companion cell
ⓒ. Sieve tube element
ⓓ. Tracheid
Correct Answer: Tracheid
Explanation: Tracheids are elongated, narrow xylem cells that conduct water through pits rather than end-wall perforations. Because water moves across pit membranes, flow is somewhat less rapid than in vessels, but this structure can reduce the risk of rapid spread of air embolisms, improving conduction safety under stress. Tracheids also provide mechanical support due to their lignified walls and are widespread across vascular plants. Vessel elements, with perforation plates, usually provide more efficient flow but can be more vulnerable to embolism spread. Sieve tubes and companion cells are phloem components and do not conduct water in xylem. Hence, tracheids are longer, narrower, lack perforation plates, and are generally safer against rapid embolism spread.
90. In a mature vascular bundle, which combination correctly lists the main conducting elements for xylem and phloem, respectively?
ⓐ. Xylem → xylem fibres; Phloem → phloem fibres
ⓑ. Xylem → vessel elements/tracheids; Phloem → sieve tube elements
ⓒ. Xylem → phloem parenchyma; Phloem → xylem parenchyma
ⓓ. Xylem → companion cells; Phloem → vessel elements
Correct Answer: Xylem → vessel elements/tracheids; Phloem → sieve tube elements
Explanation: The principal conducting elements of xylem are vessel elements and tracheids, which move water and minerals through lignified, hollow pathways. The principal conducting elements of phloem are sieve tube elements, which transport sugars and other organic solutes through sieve plates under pressure flow. While fibres and parenchyma occur in both xylem and phloem and contribute to support and storage, they are not the primary long-distance conduits. Companion cells support sieve tubes but are not the main conducting tubes themselves. This core identification is essential for linking structure to transport function in vascular tissues. Therefore, xylem conduction is mainly via vessel elements/tracheids and phloem conduction mainly via sieve tube elements.
91. The plant cuticle is best defined as:
ⓐ. A waxy, hydrophobic layer secreted by epidermal cells over the outer cell wall
ⓑ. A lignified secondary wall layer formed inside xylem vessels for conduction
ⓒ. A suberized layer formed by cork cambium to replace epidermis in old stems
ⓓ. A cellulose-free layer found only in root hairs for mineral absorption
Correct Answer: A waxy, hydrophobic layer secreted by epidermal cells over the outer cell wall
Explanation: The cuticle is a non-cellular protective covering deposited on the external surface of the epidermis, mainly on aerial parts of the plant. It is secreted by epidermal cells and lies over their outer cell wall, forming a hydrophobic barrier. This layer reduces non-stomatal (cuticular) water loss and offers protection against mechanical injury and pathogen entry. Because it is hydrophobic, it also limits wetting and excessive leaching of solutes from the surface. The cuticle’s presence and thickness vary with habitat, often being well-developed in dry conditions. Therefore, it is best described as a waxy hydrophobic layer secreted by epidermal cells on the outer surface.
92. The major chemical components most closely associated with the cuticle are:
ⓐ. Cutin and waxes
ⓑ. Lignin and cellulose
ⓒ. Pectin and hemicellulose only
ⓓ. Chitin and keratin
Correct Answer: Cutin and waxes
Explanation: The cuticle primarily consists of cutin, a lipid-based polymer, along with embedded and surface waxes that enhance hydrophobicity. These substances make the cuticle water-repellent and reduce uncontrolled water loss from epidermal surfaces. Waxes can occur as a smooth film or crystalline deposits, strengthening the barrier against evaporation and external chemical entry. This composition also contributes to protection from microbes by limiting surface moisture retention. Lignin is characteristic of secondary walls in support and conducting tissues, not the cuticle, while cellulose and pectin are major cell wall components. Hence, cutin and waxes are the key chemical components of the cuticle.
93. Which change would most directly reduce cuticular transpiration from a leaf surface?
ⓐ. Increasing the number of stomata per unit area on the lower epidermis
ⓑ. Making the cuticle thinner to allow faster diffusion of gases
ⓒ. Increasing cuticle thickness and surface wax deposition
ⓓ. Reducing xylem vessel diameter to slow water delivery to leaves
Correct Answer: Increasing cuticle thickness and surface wax deposition
Explanation: Cuticular transpiration refers to water loss through the epidermal surface outside stomata, and it is strongly influenced by the cuticle’s barrier properties. A thicker cuticle with greater wax deposition increases hydrophobicity and lengthens the diffusion pathway for water vapor, thereby reducing non-stomatal water loss. This is a common adaptive feature in plants exposed to dry, windy, or high-radiation environments. Stomatal number affects stomatal transpiration, not cuticular loss directly, and thinning the cuticle would typically increase surface water loss. Xylem diameter relates to water transport capacity but does not directly form the diffusion barrier at the surface. Therefore, increasing cuticle thickness and wax deposition most directly reduces cuticular transpiration.
94. A thick cuticle is most likely to be an adaptive advantage in plants growing under:
ⓐ. Permanently submerged aquatic conditions
ⓑ. Xeric conditions with high evaporation demand
ⓒ. Deep shade with constantly high humidity and low wind
ⓓ. Nutrient-rich soils where uptake is the main limitation
Correct Answer: Xeric conditions with high evaporation demand
Explanation: In dry habitats, plants face strong evaporative demand due to low humidity, high temperature, intense sunlight, or wind, which increases water loss risk. A thick cuticle provides a stronger barrier against cuticular transpiration by reducing the rate of water vapor diffusion from the epidermal surface. This helps conserve water and supports survival when water availability is limited or intermittent. Such a cuticle can also reduce surface wetting and protect against heat and radiation stress. In submerged aquatic conditions, a thick cuticle is generally less critical for water conservation, and in consistently humid shade its advantage is reduced. Hence, thick cuticle development is especially advantageous in xeric environments.
95. Which statement best explains why the cuticle can influence gas exchange even though stomata are the main route?
ⓐ. Cuticle blocks all stomata permanently, preventing any diffusion of gases
ⓑ. Cuticle increases the number of stomata formed during leaf development
ⓒ. Cuticle actively pumps CO₂ into epidermal cells to support photosynthesis
ⓓ. Cuticle reduces diffusion across the epidermal surface, so most gas exchange is directed through stomata
Correct Answer: Cuticle reduces diffusion across the epidermal surface, so most gas exchange is directed through stomata
Explanation: The cuticle is largely impermeable to water and also restricts diffusion of gases across the epidermal surface. Because this surface pathway is limited, plants rely on stomata as controlled openings to balance CO₂ entry with water vapor loss. In effect, the cuticle forces gas exchange to occur mainly through regulated stomatal pores rather than across the entire leaf surface. This improves physiological control, allowing plants to open or close stomata depending on environmental conditions. The cuticle does not “pump” gases and does not permanently block stomata; instead, it limits uncontrolled diffusion through the epidermis. Therefore, by restricting surface diffusion, the cuticle channels gas exchange through stomata.
96. Which plant surface is typically expected to have the least-developed cuticle under normal conditions?
ⓐ. Upper surface of a mature leaf
ⓑ. Young green stem epidermis
ⓒ. Fruit epidermis exposed to air
ⓓ. Absorbing region of young roots (root hair zone)
Correct Answer: Absorbing region of young roots (root hair zone)
Explanation: The cuticle is most prominent on aerial epidermal surfaces where reducing water loss and preventing pathogen entry are critical. In contrast, the absorbing region of young roots must allow efficient uptake of water and minerals from the soil solution, so a thick hydrophobic cuticle would hinder absorption. Root hairs, which greatly increase surface area for uptake, are typically not covered by a heavy cuticle for the same reason. Aerial parts like leaves, young stems, and fruits generally show a more developed cuticle because they face direct exposure to drying air and fluctuating external conditions. This functional difference reflects how epidermal specializations match organ roles. Hence, the root hair zone is expected to have the least-developed cuticle.
97. If a plant leaf has stomata mainly on the lower surface, which cuticle-related feature would best help minimize overheating while still reducing water loss?
ⓐ. A moderately thick cuticle with waxes that reflect some radiation on the upper surface
ⓑ. A complete absence of cuticle so evaporative cooling always remains maximal
ⓒ. A cuticle made primarily of lignin so light is absorbed and heat increases
ⓓ. A cuticle restricted only to stomatal pores while the rest of epidermis stays bare
Correct Answer: A moderately thick cuticle with waxes that reflect some radiation on the upper surface
Explanation: Surface waxes can increase reflectance of incoming radiation, reducing heat load on the leaf, while a cuticle still limits cuticular transpiration. When stomata are concentrated on the lower surface, the upper surface can prioritize protection from direct sunlight and drying air, and a waxy cuticle helps achieve this balance. A complete absence of cuticle would greatly increase uncontrolled water loss and surface damage risk. Lignin is not a typical cuticle component and would not serve the same surface barrier function. The cuticle is a surface layer over epidermal cells rather than being restricted only to stomatal pores. Therefore, a moderately thick, waxy upper cuticle that reflects some radiation best supports reduced overheating while conserving water.
98. The “waxy bloom” seen on some fruits and leaves is most directly due to:
ⓐ. Thickening of cellulose microfibrils in the epidermal cell wall
ⓑ. Epicuticular wax deposits on the cuticle surface
ⓒ. Suberin deposition in endodermal cell walls
ⓓ. Lignification of guard cells around stomata
Correct Answer: Epicuticular wax deposits on the cuticle surface
Explanation: Waxy bloom is commonly caused by epicuticular waxes that crystallize or deposit on the outermost surface of the cuticle. These wax deposits increase water repellency, reduce surface wetting, and can lower water loss by adding an additional diffusion barrier. They may also provide protection against pathogens and reduce damage from sunlight by altering reflectance. This visible “bloom” is a surface phenomenon and is not due to cellulose thickening in the wall beneath. Suberin is characteristic of certain internal protective barriers and periderm, not fruit surface bloom. Lignification is not the primary cause of the waxy appearance. Hence, epicuticular wax deposits on the cuticle surface best explain waxy bloom.
99. A researcher removes surface waxes from a leaf but leaves the cutin matrix largely intact. What is the most likely immediate effect?
ⓐ. Reduced cuticular water loss because diffusion is now blocked by cutin alone
ⓑ. Increased water loss from the surface because the barrier is weakened
ⓒ. No change in water loss because waxes have no role in hydrophobicity
ⓓ. Immediate stoppage of phloem transport due to epidermal damage
Correct Answer: Increased water loss from the surface because the barrier is weakened
Explanation: Surface waxes are a critical component of the cuticle’s hydrophobic barrier and contribute strongly to limiting cuticular transpiration. Removing waxes reduces the resistance to diffusion of water vapor from the epidermal surface, so non-stomatal water loss typically increases. Although the cutin matrix still provides some barrier function, waxes often represent the more effective diffusion-limiting layer, especially at the surface. This change can also increase surface wetting and susceptibility to pathogens because water may remain longer on the epidermis. The effect is primarily on surface permeability, not on internal transport like phloem flow. Therefore, removing surface waxes is most likely to increase cuticular water loss.
100. Which statement most accurately compares cuticle function with stomatal control in water conservation?
ⓐ. Cuticle mainly reduces cuticular transpiration, while stomata regulate the major adjustable pathway of water loss
ⓑ. Cuticle opens and closes like guard cells to control transpiration dynamically
ⓒ. Cuticle is the main pathway for bulk water loss, while stomata are minor and fixed
ⓓ. Cuticle regulates sugar transport, while stomata regulate mineral transport
Correct Answer: Cuticle mainly reduces cuticular transpiration, while stomata regulate the major adjustable pathway of water loss
Explanation: The cuticle acts as a relatively fixed protective barrier that reduces water loss through the epidermal surface outside stomata, limiting cuticular transpiration. Stomata, controlled by guard cells, provide a regulated and adjustable route for gas exchange and water vapor loss, making stomatal transpiration the major variable component of water loss. Together, they allow plants to conserve water while still permitting CO₂ entry for photosynthesis. The cuticle does not actively open and close, whereas stomatal aperture changes in response to environmental and internal signals. This division of roles is central to leaf water balance. Hence, the cuticle limits baseline cuticular loss while stomata control the major adjustable pathway of transpiration.