Timer: Off
Random: Off
101. Stomata are best described as:
ⓐ. Openings in xylem vessels that allow rapid evaporation of water
ⓑ. Pores in the epidermis bordered by guard cells that regulate gas exchange and transpiration
ⓒ. Permanent holes in the cuticle that cannot be closed once formed
ⓓ. Gaps between sclerenchyma fibres that store oxygen for respiration
Correct Answer: Pores in the epidermis bordered by guard cells that regulate gas exchange and transpiration
Explanation: Stomata are microscopic pores present in the epidermis of leaves and young stems, each bordered by specialized guard cells. By changing their turgor, guard cells open or close the stomatal pore, thereby regulating CO₂ entry for photosynthesis and controlling water vapor loss through transpiration. This regulation allows plants to balance carbon gain with water conservation under changing environmental conditions. Stomata are not part of xylem and are not fixed holes; they are dynamic structures with physiological control. Their location in the epidermal tissue system makes them key gateways between internal air spaces and the atmosphere. Therefore, stomata are epidermal pores controlled by guard cells for gas exchange and transpiration regulation.
102. Which change most directly causes stomatal opening in typical guard cells?
ⓐ. Loss of turgor in guard cells due to water خروج (outflow)
ⓑ. Lignification of guard cell walls to make them rigid
ⓒ. Thickening of cuticle over the stomatal pore
ⓓ. Increase in turgor in guard cells due to water entry
Correct Answer: Increase in turgor in guard cells due to water entry
Explanation: Stomatal opening occurs when guard cells become turgid, meaning they gain water and develop higher internal pressure against their walls. This turgor change alters guard cell shape so the stomatal pore widens, allowing gas exchange. The mechanism relies on osmotic movement of water into guard cells after solute accumulation, which increases their water potential gradient. When guard cells lose water and become flaccid, the pore closes, reducing water loss. Cuticle thickness does not directly create opening, and lignification would restrict the flexible movements needed for stomatal function. Hence, increased guard cell turgor due to water entry is the direct cause of stomatal opening.
103. Which structural feature of guard cells most directly supports their ability to open the stomatal pore?
ⓐ. Uniform wall thickness in all directions, causing equal expansion
ⓑ. Thicker inner wall (toward pore) and relatively thinner outer wall, causing bending on turgor gain
ⓒ. Complete absence of cellulose microfibrils, making walls dissolve easily
ⓓ. Suberized walls that prevent any water movement into guard cells
Correct Answer: Thicker inner wall (toward pore) and relatively thinner outer wall, causing bending on turgor gain
Explanation: Guard cells have a characteristic wall architecture where the inner wall facing the stomatal pore is thicker and less extensible than the outer wall. When turgor increases, the outer wall stretches more, and the differential expansion causes guard cells to curve outward, opening the pore. The orientation of cellulose microfibrils also contributes by guiding the direction of expansion and curvature. This specialized structure enables a reversible mechanical response to changes in turgor. Uniform wall thickness would not create the same controlled bending needed for a pore mechanism. Therefore, the thicker inner wall and thinner outer wall arrangement is a key structural basis for stomatal opening.
104. In many flowering plants, stomata are typically more abundant on which surface of a dorsiventral (bifacial) leaf, helping reduce direct water loss?
ⓐ. Upper epidermis only
ⓑ. Only on leaf veins, never on lamina
ⓒ. Both surfaces equally in all habitats
ⓓ. Lower epidermis
Correct Answer: Lower epidermis
Explanation: In many dorsiventral leaves, stomata are more numerous on the lower epidermis, which is generally less exposed to direct sunlight and wind. This arrangement reduces transpiration compared to having many stomata on the upper surface, while still allowing sufficient CO₂ entry for photosynthesis. The lower surface often experiences a more humid boundary layer, further limiting excessive water loss through open stomata. While some plants have stomata on both sides, the common pattern for many broad leaves is higher stomatal density below. This distribution reflects a functional compromise between gas exchange and water conservation. Hence, stomata are typically more abundant on the lower epidermis in dorsiventral leaves.
105. Which process is most directly regulated by stomata during daytime in green leaves?
ⓐ. Water and mineral uptake by roots from soil solution
ⓑ. Diffusion of CO₂ into the leaf for photosynthesis and loss of water vapor by transpiration
ⓒ. Long-distance movement of sugars through sieve tubes to roots
ⓓ. Secondary growth producing new xylem and phloem by cambium
Correct Answer: Diffusion of CO₂ into the leaf for photosynthesis and loss of water vapor by transpiration
Explanation: Stomata serve as adjustable gates that control exchange of gases between the atmosphere and internal leaf air spaces. When stomata open, CO₂ diffuses inward to support photosynthesis, while water vapor diffuses outward, contributing to transpiration. By opening and closing, stomata regulate both carbon gain and water loss, making them central to plant water-use efficiency and productivity. Root uptake, sugar translocation, and cambial secondary growth are important but are not directly controlled by stomatal aperture. The stomatal pore directly determines the diffusion rate of CO₂ and water vapor. Therefore, stomata regulate CO₂ entry and transpiration during daytime.
106. A plant closes its stomata during hot, dry afternoons. What is the most immediate advantage of this response?
ⓐ. Increased CO₂ uptake to maximize photosynthesis
ⓑ. Increased mineral absorption by root hairs due to lower transpiration
ⓒ. Reduced loss of water vapor, helping prevent excessive dehydration
ⓓ. Formation of thicker cuticle within minutes to block evaporation
Correct Answer: Reduced loss of water vapor, helping prevent excessive dehydration
Explanation: Hot, dry conditions increase the vapor pressure gradient between the leaf interior and the atmosphere, strongly promoting water loss. By closing stomata, the plant reduces stomatal transpiration, which is the major adjustable component of water loss from leaves. This helps maintain leaf water potential, prevents wilting, and protects physiological processes from damage due to dehydration. Although closure may reduce CO₂ entry and limit photosynthesis, the immediate survival benefit is water conservation. Mineral absorption may eventually be affected, but the primary direct effect of stomatal closure is reduced water vapor diffusion. Therefore, the most immediate advantage is preventing excessive dehydration by lowering water loss.
107. Which statement best explains why guard cells, unlike most other epidermal cells, often contain chloroplasts?
ⓐ. Guard cell chloroplasts are mainly for storing starch permanently as a structural material
ⓑ. Guard cell chloroplasts support energy needs and metabolite production linked to stomatal movements
ⓒ. Guard cell chloroplasts are required to lignify the walls for permanent opening
ⓓ. Guard cell chloroplasts exist only to increase leaf color intensity for pollinators
Correct Answer: Guard cell chloroplasts support energy needs and metabolite production linked to stomatal movements
Explanation: Guard cells often contain chloroplasts, which can contribute ATP and metabolic intermediates that support active ion transport and osmotic adjustments needed for opening and closing. Stomatal movement requires regulated solute accumulation and release, which can be energetically demanding and responsive to light. Chloroplasts also allow guard cells to respond directly to light signals, integrating photosynthetic conditions with stomatal behavior. Most other epidermal cells typically lack chloroplasts because their primary roles are protection and barrier formation rather than metabolism-driven movement. The chloroplast presence in guard cells is therefore functional, not decorative or for lignification. Hence, guard cell chloroplasts help meet energy and metabolic requirements associated with stomatal regulation.
108. Which pair correctly matches a stomatal apparatus component with its main role?
ⓐ. Guard cells → control pore aperture; Subsidiary cells → support guard cell function and ion/water relations
ⓑ. Xylem vessels → control pore aperture; Tracheids → support guard cell function
ⓒ. Sieve tubes → control pore aperture; Companion cells → form stomatal pore
ⓓ. Cork cells → control pore aperture; Phellogen → opens and closes stomata
Correct Answer: Guard cells → control pore aperture; Subsidiary cells → support guard cell function and ion/water relations
Explanation: The stomatal apparatus includes guard cells that directly form the pore and actively regulate its opening and closing by changing turgor. Subsidiary cells, when present, are specialized epidermal cells adjacent to guard cells that can help buffer ion and water movements and provide structural and physiological support for efficient stomatal function. This arrangement can improve responsiveness and stability of guard cell movements under varying conditions. Vascular elements like xylem and phloem are unrelated to pore mechanics, and cork tissues are protective layers not involved in stomatal regulation. The correct functional pairing is therefore guard cells controlling the aperture and subsidiary cells assisting and supporting the process. Hence, the matched roles of guard and subsidiary cells best describe stomatal apparatus components.
109. A leaf has stomata on both upper and lower surfaces. Which term best describes this condition?
ⓐ. Hypostomatic
ⓑ. Epistomatic
ⓒ. Amphistomatic
ⓓ. Astomatic
Correct Answer: Amphistomatic
Explanation: Leaves are classified based on stomatal distribution on their surfaces. Amphistomatic leaves have stomata on both the upper and lower epidermis, allowing gas exchange from both sides. This arrangement can support higher photosynthetic rates in high-light environments by increasing diffusion capacity, though it may also increase potential water loss. Hypostomatic leaves mainly have stomata on the lower surface, while epistomatic leaves mainly have them on the upper surface. Astomatic leaves lack stomata, which is uncommon for typical terrestrial leaves. Therefore, a leaf with stomata on both surfaces is correctly termed amphistomatic.
110. Under which condition would stomatal closure most directly limit photosynthesis in the short term?
ⓐ. When CO₂ diffusion into the leaf is reduced due to a narrowed stomatal pore
ⓑ. When xylem lignification increases, making stems more rigid
ⓒ. When cuticle becomes thicker in the root hair zone
ⓓ. When phloem fibres increase in number around vascular bundles
Correct Answer: When CO₂ diffusion into the leaf is reduced due to a narrowed stomatal pore
Explanation: Photosynthesis depends on a steady supply of CO₂ to mesophyll cells, and the primary gateway for CO₂ entry is the stomatal pore. When stomata close, diffusion of CO₂ into internal air spaces declines, lowering the internal CO₂ concentration and directly limiting the rate of carbon fixation. This effect can occur rapidly, even if light and chloroplast function remain adequate, because substrate availability becomes the limiting factor. Structural changes like xylem lignification or increased fibres do not immediately restrict CO₂ diffusion into the leaf. The cuticle in roots is unrelated to leaf CO₂ intake. Therefore, stomatal closure limits photosynthesis in the short term by reducing CO₂ diffusion into the leaf.
111. In the epidermal tissue system, trichomes are best described as:
ⓐ. Open pores bordered by guard cells that regulate transpiration
ⓑ. A waxy non-cellular layer deposited over the epidermis
ⓒ. Vascular strands that transport water and minerals upward
ⓓ. Epidermal outgrowths (hair-like projections) arising from epidermal cells
Correct Answer: Epidermal outgrowths (hair-like projections) arising from epidermal cells
Explanation: Trichomes are hair-like or scale-like outgrowths produced by epidermal cells, commonly present on aerial parts such as leaves and young stems. They can be unicellular or multicellular and may be branched or unbranched, depending on the plant. Because they project above the surface, they modify the microclimate near the epidermis and can reduce direct exposure to wind and sunlight. Trichomes also play roles in protection, including reducing herbivory and limiting pathogen contact with the surface. Some trichomes are glandular and secrete substances, adding a chemical defense component. Hence, trichomes are epidermal outgrowths formed from epidermal cells.
112. Which function is most directly linked to dense, non-glandular trichomes on leaf surfaces in many plants?
ⓐ. Rapid long-distance conduction of sugars to roots
ⓑ. Reduction of water loss by trapping a humid boundary layer near the epidermis
ⓒ. Production of secondary xylem to strengthen the stem
ⓓ. Opening and closing of pores to control CO₂ entry
Correct Answer: Reduction of water loss by trapping a humid boundary layer near the epidermis
Explanation: Dense non-glandular trichomes create a protective “hairy” layer above the epidermis that slows air movement across the surface. This reduces the water vapor diffusion gradient by maintaining a more humid boundary layer close to the leaf, thereby lowering transpiration. Trichomes can also reflect excess light and reduce surface temperature, further decreasing evaporative demand. Their physical barrier effect is especially useful in dry, windy, or high-radiation environments. While trichomes may also deter herbivores, the most direct physiological link here is reduced water loss through microclimate modification. Therefore, dense non-glandular trichomes help conserve water by trapping a humid boundary layer.
113. Glandular trichomes are best identified by which defining feature?
ⓐ. They secrete substances such as oils, resins, or mucilage onto the plant surface
ⓑ. They form lignified tubes for fast water transport under tension
ⓒ. They develop sieve plates for pressure-driven sugar translocation
ⓓ. They act as pores that open and close with guard cell movement
Correct Answer: They secrete substances such as oils, resins, or mucilage onto the plant surface
Explanation: Glandular trichomes are specialized epidermal outgrowths that produce and release secretions to the plant surface. These secretions can include essential oils, resins, mucilage, or other compounds that deter herbivores, inhibit microbes, or reduce water loss by adding surface coatings. Structurally, glandular trichomes often have a secretory head region supported by a stalk, enabling storage and controlled release of materials. Their function extends plant defense beyond physical barriers to chemical protection. This distinguishes them from non-glandular hairs that primarily provide mechanical shielding. Hence, secretion of surface substances is the defining feature of glandular trichomes.
114. Which statement best distinguishes trichomes from thorns in terms of origin?
ⓐ. Trichomes arise from epidermal cells, while thorns are modified stems or branches
ⓑ. Trichomes arise from vascular cambium, while thorns arise from epidermis
ⓒ. Trichomes are always modified leaves, while thorns are always modified roots
ⓓ. Trichomes form only in roots, while thorns form only in leaves
Correct Answer: Trichomes arise from epidermal cells, while thorns are modified stems or branches
Explanation: Trichomes are epidermal outgrowths derived from epidermal cells and are typically superficial structures on the plant surface. Thorns, in contrast, are hard, pointed structures that originate from deeper tissues and are commonly modified stems or branches, making them anatomically more complex and strongly lignified. This difference in origin explains why thorns are rigid and integrated with the plant’s vascular system, whereas trichomes are surface projections. Trichomes may deter herbivores by irritation or secretion, but they are not equivalent to woody defensive spines. Understanding the tissue origin prevents confusion between surface hairs and modified shoot structures. Therefore, trichomes arise from epidermis, while thorns arise from modified stems/branches.
115. A student notices tiny hairs on a leaf that feel rough and reduce insect feeding. Which mechanism best explains this protective effect of trichomes?
ⓐ. They generate root pressure that pushes insects away from the surface
ⓑ. They act as a physical barrier that makes attachment and feeding more difficult
ⓒ. They convert sugars into starch so insects cannot detect the leaf
ⓓ. They replace stomata and stop all gas exchange to starve insects
Correct Answer: They act as a physical barrier that makes attachment and feeding more difficult
Explanation: Many leaf trichomes function as mechanical defenses by forming a surface barrier that interferes with insect movement, attachment, and access to epidermal tissues. Dense or stiff hairs can physically block mouthparts, slow feeding, and reduce the success of small herbivores and egg laying. Some trichomes also irritate insects or cause abrasion, increasing the deterrent effect even without chemical secretion. This structural barrier can lower the likelihood of direct epidermal damage and may also reduce pathogen contact by limiting surface interactions. The protective role is therefore largely based on hindering access rather than altering internal transport processes. Hence, trichomes protect by acting as a physical barrier to insect attachment and feeding.
116. Which example best represents a common ecological advantage of reflective trichomes on leaf surfaces in dry habitats?
ⓐ. Faster phloem loading by increasing companion cell activity
ⓑ. Increased secondary growth by stimulating cambial division
ⓒ. Enhanced mineral uptake by thickening the root endodermis
ⓓ. Reduced leaf temperature and water loss by reflecting excess solar radiation
Correct Answer: Reduced leaf temperature and water loss by reflecting excess solar radiation
Explanation: Reflective trichomes increase the leaf’s ability to reflect incoming sunlight, reducing the amount of radiation absorbed and thereby lowering leaf surface temperature. A cooler leaf reduces evaporative demand, which helps limit transpiration and conserve water in dry environments. This physical shading effect can also protect photosynthetic tissues from heat and light stress, improving performance during intense sunlight. The benefit is especially pronounced in habitats where high radiation and low humidity would otherwise cause rapid dehydration. This adaptation complements cuticle and stomatal regulation by reducing the driving forces for water loss. Therefore, reflective trichomes provide an advantage by lowering leaf temperature and reducing water loss through radiation reflection.
117. Which statement is most accurate about the cellular organization of trichomes in flowering plants?
ⓐ. Trichomes are always multicellular and always branched
ⓑ. Trichomes are always unicellular and only occur on stems
ⓒ. Trichomes may be unicellular or multicellular and may be branched or unbranched
ⓓ. Trichomes are non-living deposits formed outside the epidermis like wax layers
Correct Answer: Trichomes may be unicellular or multicellular and may be branched or unbranched
Explanation: Trichomes show wide structural diversity across flowering plants, reflecting different functional needs. Some trichomes are unicellular and unbranched, while others are multicellular and may be branched, stellate (star-shaped), or scale-like. This variability influences how effectively they reduce water loss, reflect light, deter herbivores, or secrete protective chemicals in glandular forms. Despite differences in form, their shared feature is epidermal origin as outgrowths from epidermal cells. They are living structures during development and are not merely external deposits like waxes. Hence, trichomes can be unicellular or multicellular and may be branched or unbranched.
118. Root hairs are often treated as a special type of epidermal outgrowth. What is their primary functional significance compared with most aerial trichomes?
ⓐ. They mainly reduce transpiration by reflecting sunlight
ⓑ. They mainly increase absorption by greatly enlarging root surface area in the soil
ⓒ. They mainly conduct water upward as hollow tubes
ⓓ. They mainly form a waterproof barrier to prevent mineral entry
Correct Answer: They mainly increase absorption by greatly enlarging root surface area in the soil
Explanation: Root hairs are epidermal outgrowths specialized to increase the effective absorptive surface area of roots in contact with soil particles and the soil solution. By extending into spaces between soil particles, they enhance uptake of water and dissolved minerals, improving the plant’s nutrient and hydration status. Unlike many aerial trichomes that commonly reduce water loss or defend against herbivores, root hairs are primarily adapted for absorption. Their thin walls and close contact with the soil environment support efficient uptake. This functional specialization explains why the root hair zone is a key site for absorption in young roots. Therefore, root hairs chiefly increase absorption by enlarging root surface area.
119. A plant shows sticky secretions on leaf hairs that trap small insects. Which structure most directly explains this observation?
ⓐ. Glandular trichomes producing adhesive secretions on the epidermal surface
ⓑ. Sclerenchyma fibres exuding resins through bordered pits
ⓒ. Vessel elements releasing mucilage through perforation plates
ⓓ. Guard cells secreting oils to close stomata permanently
Correct Answer: Glandular trichomes producing adhesive secretions on the epidermal surface
Explanation: Sticky secretions on leaf hairs are characteristic of glandular trichomes, which can produce and release viscous substances onto the plant surface. These secretions can trap insects, deter herbivores, and reduce microbial growth, functioning as a chemical and mechanical defense combined. The presence of a secretory head allows accumulation and release of adhesive materials in response to environmental interactions. Such secretions are produced by epidermal-derived structures rather than by vascular conducting elements, which are specialized for transport. Guard cells regulate stomatal pores and are not responsible for sticky surface secretions. Hence, glandular trichomes best explain sticky leaf hairs that trap insects.
120. Which statement best explains how trichomes can help reduce pathogen infection on leaves?
ⓐ. Trichomes directly transport antibodies to the leaf surface
ⓑ. Trichomes replace the cuticle and remove all surface barriers
ⓒ. Trichomes physically reduce surface contact and may trap moisture away from epidermal cells, limiting infection opportunities
ⓓ. Trichomes convert xylem into phloem to block pathogen movement
Correct Answer: Trichomes physically reduce surface contact and may trap moisture away from epidermal cells, limiting infection opportunities
Explanation: Trichomes can reduce pathogen success by acting as a physical barrier that limits direct contact between microbes and the epidermal surface. A hairy surface can interfere with spore attachment and germination near epidermal cells and can alter the microenvironment at the surface, sometimes reducing prolonged wet contact on the epidermis. In glandular forms, secretions may also inhibit microbial growth, strengthening defense further. By increasing the distance from the epidermis and complicating access, trichomes reduce the probability that pathogens reach suitable entry points. This is a protective strategy based on surface architecture rather than changes in vascular transport. Therefore, trichomes help reduce infection by limiting contact and modifying surface conditions that pathogens need for successful establishment.
121. Root hairs are best described as:
ⓐ. Multicellular epidermal outgrowths on leaves that secrete oils
ⓑ. Lignified projections of xylem that increase water conduction
ⓒ. Unicellular tubular extensions of root epidermal cells that increase absorptive surface area
ⓓ. Open pores in roots bordered by guard cells for gas exchange
Correct Answer: Unicellular tubular extensions of root epidermal cells that increase absorptive surface area
Explanation: Root hairs are unicellular, tube-like extensions that arise from specific epidermal cells of young roots and project into the soil. Their main significance is that they greatly increase the surface area available for absorption of water and mineral ions from the soil solution. Because they are thin-walled and closely contact soil particles, they create an efficient interface for uptake. Root hairs are not vascular structures, so they do not conduct water like xylem elements. They also are not stomata-like pores, since roots generally lack stomatal regulation structures. Therefore, root hairs are unicellular epidermal extensions that enhance absorption.
122. Root hairs are typically most abundant in which region of a growing root?
ⓐ. Zone of maturation (differentiation), just behind the elongation zone
ⓑ. Root cap, at the very tip that protects the meristem
ⓒ. Zone of cell division (meristematic zone), immediately behind the root cap
ⓓ. Mature older root regions where periderm has formed
Correct Answer: Zone of maturation (differentiation), just behind the elongation zone
Explanation: Root hairs develop when epidermal cells differentiate in the zone of maturation, which lies behind the elongation zone. In this region, cells complete their specialization and certain epidermal cells form hair-like extensions to maximize absorption. The root cap is protective and does not produce root hairs, while the meristematic zone focuses on cell division rather than full differentiation. In older regions, epidermal tissues may be replaced or become less absorptive due to aging and protective modifications, reducing root hair presence. This placement ensures root hairs form where cells are mature enough to function but still young and active in uptake. Hence, root hairs are most abundant in the zone of maturation.
123. Which feature most directly makes root hairs efficient for absorption?
ⓐ. Thick suberized walls that prevent backflow of water
ⓑ. Thin, permeable cell walls with a large vacuole that supports water entry by osmosis
ⓒ. Heavy lignification that keeps the hair rigid for conduction
ⓓ. A thick waxy cuticle that reduces water loss to soil
Correct Answer: Thin, permeable cell walls with a large vacuole that supports water entry by osmosis
Explanation: Root hairs absorb efficiently because they have thin, non-lignified, permeable cell walls that allow water and dissolved ions to move across the surface. A large vacuole helps maintain osmotic gradients, enabling water entry into the cell and onward movement into the root cortex. The absence of heavy cuticle and suberin in the root hair zone supports uptake rather than blocking it. Lignification would reduce permeability and is associated with support tissues, not absorptive surfaces. The overall design prioritizes intimate soil contact and rapid exchange. Therefore, thin permeable walls and a large vacuole make root hairs highly effective in absorption.
124. If most root hairs of a seedling are damaged by transplantation, what is the most immediate likely effect?
ⓐ. The plant’s ability to perform photosynthesis drops instantly due to loss of chloroplasts
ⓑ. Water and mineral uptake decreases temporarily, leading to wilting risk until new hairs develop
ⓒ. Secondary growth stops because cambium cannot divide without root hairs
ⓓ. Xylem vessels collapse because root hairs provide mechanical support to xylem
Correct Answer: Water and mineral uptake decreases temporarily, leading to wilting risk until new hairs develop
Explanation: Root hairs are the primary absorptive interface for water and mineral ions in young roots, so damaging them reduces uptake capacity immediately. This can cause a transient water deficit in the shoot, increasing the risk of wilting, especially under warm or dry conditions. Over time, new root hairs can form in newly matured root regions, restoring absorption. Photosynthesis may be affected indirectly later if water stress persists, but the immediate impact is reduced uptake. Cambial activity and xylem mechanical strength are not directly dependent on root hairs. Hence, the most immediate effect is decreased water and mineral absorption with short-term wilting risk.
125. Which statement best explains why root hairs are generally absent very close to the root tip?
ⓐ. The root tip is covered by a protective root cap and nearby cells are still dividing or elongating, not yet differentiated
ⓑ. The root tip has stomata that replace the need for hairs
ⓒ. The root tip is made only of dead sclerenchyma, so hairs cannot form
ⓓ. The root tip is always covered by thick periderm that blocks hair formation
Correct Answer: The root tip is covered by a protective root cap and nearby cells are still dividing or elongating, not yet differentiated
Explanation: Root hairs form when epidermal cells differentiate, which happens in the maturation zone behind the elongation zone. Near the tip, the root cap protects the meristem, and cells just behind it are engaged in active division and elongation, so they are not yet specialized enough to produce hairs. Hair formation requires stable cell identity and wall extension into a tubular projection, which is characteristic of differentiated epidermal cells. Roots also do not rely on stomata at the tip, and the tip is not composed of dead sclerenchyma. Periderm formation is typical of older regions, not the young apex. Therefore, root hairs are absent near the tip because cells there are not yet differentiated.
126. Root hairs mainly increase absorption because they:
ⓐ. Reduce the effective surface area so water enters faster per unit area
ⓑ. Block soil pores to raise water pressure around roots
ⓒ. Greatly increase the root’s surface area in contact with soil solution and particles
ⓓ. Convert mineral ions into sugars at the epidermis
Correct Answer: Greatly increase the root’s surface area in contact with soil solution and particles
Explanation: The key advantage of root hairs is the massive increase in surface area they provide, allowing more contact between the root and the thin water film surrounding soil particles. This expanded interface improves diffusion and uptake of mineral ions and facilitates water absorption driven by osmotic gradients. Root hairs also help penetrate microspaces between particles, reaching moisture that thicker roots cannot access as effectively. They do not create pressure by blocking pores, and they do not chemically convert ions into sugars at the surface. The benefit is primarily physical and anatomical—more contact area for exchange. Hence, root hairs increase absorption by greatly increasing the root’s contact surface with soil solution.
127. Compared with most aerial epidermal surfaces, the root hair region is best adapted for absorption because it typically has:
ⓐ. A very thick cuticle to prevent entry of external water
ⓑ. Numerous stomata for regulated uptake of minerals
ⓒ. A ring of cork cells replacing epidermis early in development
ⓓ. Little to no cuticle and thin walls, allowing easy entry of water and ions
Correct Answer: Little to no cuticle and thin walls, allowing easy entry of water and ions
Explanation: Absorption requires permeability, so the root hair zone is specialized with thin, non-suberized walls and minimal cuticle deposition. This contrasts with aerial epidermis, where a cuticle is beneficial for reducing water loss. By avoiding thick hydrophobic barriers, the root hair region allows water to move inward and ions to enter via transport processes across the plasma membrane. The absence of stomata in roots aligns with their role in uptake rather than gas exchange control. Early replacement by cork would hinder absorption, so such protective layers are not typical in the active hair zone. Therefore, minimal cuticle and thin walls make the root hair region well-suited for absorption.
128. A student claims: “Root hairs are permanent and remain functional for the entire life of the root.” Which statement best corrects this?
ⓐ. Root hairs are short-lived; they are replaced as the root grows, and older regions often lose hairs as tissues mature
ⓑ. Root hairs become vessels later, so they persist as conducting tubes
ⓒ. Root hairs persist but close like stomata when water is scarce
ⓓ. Root hairs are made of sclerenchyma, so they remain unchanged for years
Correct Answer: Root hairs are short-lived; they are replaced as the root grows, and older regions often lose hairs as tissues mature
Explanation: Root hairs are typically transient structures that develop in the maturation zone and function for a limited period. As the root elongates, new hairs form in newly matured regions, while older hairs often die off or are lost as the outer tissues age and protective changes reduce absorptive capacity. This turnover matches the dynamic movement of the root through soil and the shifting zones of active absorption. Root hairs do not transform into xylem vessels, and they do not operate via opening and closing like stomata. Their thin-walled living nature supports active uptake but does not imply long-term persistence. Hence, root hairs are short-lived and are continually replaced as the root grows.
129. Which scenario would most directly reduce root hair effectiveness in mineral uptake even if root hairs are present?
ⓐ. Increased light intensity on leaves during midday
ⓑ. A well-aerated, moist soil with fine particles
ⓒ. Dry soil conditions that reduce the water film around soil particles, limiting ion movement to hairs
ⓓ. Increased wax deposition on the leaf cuticle
Correct Answer: Dry soil conditions that reduce the water film around soil particles, limiting ion movement to hairs
Explanation: Mineral uptake by root hairs depends strongly on the presence of a continuous water film around soil particles, which allows ions to diffuse or be transported toward the root surface. Under dry conditions, this water film becomes discontinuous and thinner, reducing ion mobility and limiting the contact between root hairs and dissolved nutrients. Even if hairs remain structurally present, the effective supply of ions to the hair surface decreases, lowering uptake rates. Leaf light intensity and leaf cuticle waxes do not directly control ion availability at the root–soil interface. Moist, well-aerated soils generally improve diffusion and uptake conditions. Therefore, dry soil that reduces the soil water film most directly decreases root hair effectiveness in mineral uptake.
130. Root hairs originate from:
ⓐ. Cortex cells that push outward through the epidermis
ⓑ. Pericycle cells that also give rise to lateral roots
ⓒ. Endodermal cells that form Casparian strips
ⓓ. Specialized epidermal cells (root epidermis) that elongate outward into tubular projections
Correct Answer: Specialized epidermal cells (root epidermis) that elongate outward into tubular projections
Explanation: Root hairs are produced by the root epidermis, specifically by specialized epidermal cells that differentiate into hair-forming cells and extend outward as tubular projections. This epidermal origin ensures the hair is positioned at the interface with soil, maximizing contact for water and mineral uptake. Cortex, pericycle, and endodermis have distinct roles: cortex mainly stores and transports inward, pericycle initiates lateral roots, and endodermis regulates entry into the stele via selective barriers. The developmental pathway of root hairs is therefore an epidermal specialization rather than an internal tissue outgrowth. Their formation is tightly linked to the maturation of epidermal cells in the absorption zone. Hence, root hairs originate from specialized epidermal cells that elongate outward.
131. In a typical dicot root, “xylem is exarch” most precisely means:
ⓐ. Protoxylem is towards the periphery and metaxylem is towards the center
ⓑ. Protoxylem is towards the center and metaxylem is towards the periphery
ⓒ. Xylem forms a continuous ring outside the phloem
ⓓ. Xylem is absent at the periphery and present only in the cortex
Correct Answer: Protoxylem is towards the periphery and metaxylem is towards the center
Explanation: Exarch arrangement describes the maturation pattern of xylem in roots, where the earliest formed xylem (protoxylem) lies closer to the outer side and later formed xylem (metaxylem) is positioned more centrally. This pattern reflects how the root vascular tissues differentiate as the organ develops. In transverse section of a dicot root, xylem and phloem are arranged radially, and the protoxylem points commonly appear at the tips of the xylem arms toward the periphery. The metaxylem vessels are larger and found closer to the center, consistent with later differentiation. This is a key anatomical feature used to identify root vascular organization. Therefore, exarch means protoxylem peripheral and metaxylem central.
132. A cross-section shows a star-shaped xylem core with protoxylem at the tips of arms. Which interpretation best matches “exarch xylem” in a dicot root?
ⓐ. The youngest xylem is at the tips and the oldest is toward the center
ⓑ. The oldest xylem is at the tips and the youngest is toward the center
ⓒ. All xylem elements mature simultaneously, so exarch has no meaning
ⓓ. Xylem maturation proceeds from center to periphery in roots
Correct Answer: The oldest xylem is at the tips and the youngest is toward the center
Explanation: In root xylem, exarch refers to protoxylem being located toward the periphery, and protoxylem is the earliest formed (oldest) xylem. In a dicot root, these protoxylem groups typically appear at the outer ends of the star-like xylem arms. As development proceeds, metaxylem (later formed, younger xylem) differentiates closer to the center and often has larger vessel elements. Thus, maturation direction is from periphery toward the center in the root. This spatial relationship between protoxylem and metaxylem is the key diagnostic point for recognizing exarch arrangement. Hence, the oldest xylem lies at the arm tips and the younger xylem is nearer the center.
133. Which feature most strongly supports that the given section is a root (not a stem) based on xylem arrangement?
ⓐ. Presence of a large central pith with vascular bundles in a ring
ⓑ. Endarch xylem with protoxylem toward the center of each bundle
ⓒ. Exarch xylem with protoxylem toward the periphery in radial vascular bundles
ⓓ. Scattered vascular bundles without a distinct endodermis
Correct Answer: Exarch xylem with protoxylem toward the periphery in radial vascular bundles
Explanation: Roots typically show radial arrangement of vascular tissues, where xylem and phloem are on different radii, and the xylem maturation pattern is exarch. Exarch xylem means protoxylem is placed toward the periphery, a common hallmark used to distinguish roots from stems in anatomy questions. Stems generally have vascular bundles arranged in a ring (dicots) or scattered (monocots) and usually show endarch xylem, where protoxylem lies toward the center of the stem. The combination of radial bundles and exarch maturation is therefore a strong root indicator. This feature aligns with typical dicot root internal structure and development. Hence, exarch xylem in radial bundles most strongly supports that the section is a root.
134. In a dicot root with exarch xylem, which statement about vessel size distribution is most accurate?
ⓐ. Smaller protoxylem elements lie peripheral, while larger metaxylem vessels lie more central
ⓑ. Larger protoxylem vessels lie central, while smaller metaxylem lie peripheral
ⓒ. Vessel size is uniform from periphery to center because maturation is simultaneous
ⓓ. Large vessels occur only in the cortex, not in the stele
Correct Answer: Smaller protoxylem elements lie peripheral, while larger metaxylem vessels lie more central
Explanation: Protoxylem differentiates first and is adapted to function while the organ is still elongating, so it typically has narrower elements and may show structural adaptations suited for early conduction. In exarch roots, protoxylem lies toward the periphery, commonly at the tips of xylem arms. Metaxylem differentiates later when elongation is reduced, so it often forms larger vessel elements positioned closer to the center. This creates a recognizable pattern in dicot root cross-sections: smaller xylem toward the outside and larger vessels more centrally. This size distribution is consistent with the developmental sequence implied by exarch arrangement. Therefore, smaller protoxylem is peripheral and larger metaxylem is more central.
135. A student says: “Exarch means phloem is outside xylem.” What is the most accurate correction for dicot root anatomy?
ⓐ. Exarch refers to phloem maturing before xylem, not their positions
ⓑ. Exarch refers to xylem maturation: protoxylem peripheral and metaxylem central
ⓒ. Exarch means xylem is always outside phloem in a complete ring
ⓓ. Exarch means endodermis is absent in roots
Correct Answer: Exarch refers to xylem maturation: protoxylem peripheral and metaxylem central
Explanation: Exarch is a term describing the direction of xylem development and the relative position of protoxylem and metaxylem, not the simple outside/inside placement of phloem relative to xylem. In roots, xylem and phloem are arranged radially on different radii, and the key point is that protoxylem forms toward the periphery while metaxylem forms toward the center. This developmental arrangement is a common anatomical criterion used to identify root sections. Confusing exarch with the radial placement of phloem leads to incorrect interpretation, because phloem position varies by radius rather than forming a single continuous outside layer. Hence, exarch correctly refers to protoxylem being peripheral and metaxylem being central.
136. In a dicot root showing exarch xylem, the maturation sequence of xylem proceeds:
ⓐ. From center to periphery
ⓑ. From periphery to center
ⓒ. Randomly without a fixed direction
ⓓ. From pith outward into cortex
Correct Answer: From periphery to center
Explanation: Exarch arrangement in roots indicates that protoxylem is located toward the periphery and metaxylem toward the center. Since protoxylem forms first and metaxylem forms later, the direction of maturation is from outer to inner positions. This means xylem differentiation progresses from the periphery toward the center of the stele. The pattern is consistent across typical roots and contrasts with stems, where endarch maturation proceeds from inside outward. Recognizing the direction helps students correctly interpret transverse sections and link structure to development. Therefore, in a dicot root, xylem maturation proceeds from periphery to center.
137. Which observation best supports that the xylem in the given dicot root is exarch rather than endarch?
ⓐ. The endodermis shows Casparian strips
ⓑ. Protoxylem is located near the center and metaxylem near the endodermis
ⓒ. Phloem is absent between xylem arms
ⓓ. Protoxylem is seen closer to the endodermis, while metaxylem is closer to the center
Correct Answer: Protoxylem is seen closer to the endodermis, while metaxylem is closer to the center
Explanation: The defining anatomical indicator of exarch xylem is the peripheral position of protoxylem relative to metaxylem. In roots, protoxylem groups lie closer to the endodermis because they occupy the outer tips of xylem arms, while metaxylem differentiates later and is located more centrally. This spatial relationship directly distinguishes exarch from endarch, where protoxylem would be nearer the center. The presence of Casparian strips is a root feature but does not distinguish exarch from endarch maturation specifically. Likewise, phloem distribution between xylem arms varies and is not the key criterion for exarch identification. Hence, protoxylem near the endodermis and metaxylem toward the center best supports exarch xylem.
138. In dicot roots, xylem is typically described as radial and exarch. The term “radial” here most directly indicates:
ⓐ. Xylem and phloem occur on alternate radii, not in the same bundle
ⓑ. Xylem surrounds phloem completely as concentric rings
ⓒ. Vascular bundles are scattered in the ground tissue
ⓓ. Xylem is arranged as a single continuous cylinder with no phloem
Correct Answer: Xylem and phloem occur on alternate radii, not in the same bundle
Explanation: Radial arrangement means xylem and phloem are positioned on different radii in the stele, typically alternating around the center. In a dicot root cross-section, xylem forms arms or patches, and phloem occurs in between these xylem arms on separate radii. This is distinct from the conjoint arrangement in stems, where xylem and phloem occur together within the same vascular bundle. The radial pattern complements the exarch maturation feature, forming a typical diagnostic combination for roots. This structural organization supports effective transport distribution in the root axis. Therefore, “radial” indicates xylem and phloem on alternate radii rather than in the same bundle.
139. A dicot root section shows tetrarch xylem. Which statement best fits the exarch nature of such xylem?
ⓐ. Four protoxylem groups lie toward the center and expand outward during maturation
ⓑ. Four xylem bundles are scattered in cortex and do not show a maturation gradient
ⓒ. Four metaxylem groups lie at the periphery, and protoxylem forms in the middle
ⓓ. Four protoxylem groups lie toward the periphery, with metaxylem positioned more centrally
Correct Answer: Four protoxylem groups lie toward the periphery, with metaxylem positioned more centrally
Explanation: Tetrarch indicates four xylem arms or protoxylem points in the root stele. In an exarch arrangement, these protoxylem groups are located toward the periphery, typically at the tips of the xylem arms close to the endodermis. As xylem matures, metaxylem elements differentiate closer to the center, often appearing larger and more centrally placed. Thus, even in tetrarch roots, the exarch criterion remains the peripheral protoxylem and central metaxylem. This combines the “number of arms” concept with the “maturation direction” concept in a single anatomical interpretation. Hence, tetrarch exarch xylem shows four peripheral protoxylem groups with more central metaxylem.
140. Which relationship between root primary growth and exarch xylem best explains why protoxylem is placed peripherally?
ⓐ. Peripheral protoxylem forms early to function during elongation, while later metaxylem forms centrally when elongation slows
ⓑ. Protoxylem forms peripherally only to increase lignification near cortex for protection
ⓒ. Protoxylem is peripherally placed to convert into phloem during secondary growth
ⓓ. Protoxylem is peripheral because roots lack endodermis, so tissues shift outward
Correct Answer: Peripheral protoxylem forms early to function during elongation, while later metaxylem forms centrally when elongation slows
Explanation: Protoxylem develops first when the root is still actively elongating, so its elements are adapted to early conduction in a growing organ. Positioning protoxylem peripherally aligns with the root’s developmental pattern, while later-formed metaxylem differentiates more centrally when elongation is reduced and larger conducting elements can form. This developmental timing and placement together define exarch xylem, emphasizing maturation from outside to inside. The arrangement is not primarily for protection via cortex lignification, nor does protoxylem convert into phloem. Roots do possess a well-defined endodermis, so absence of endodermis is incorrect. Therefore, peripheral protoxylem reflects early function during elongation and later central metaxylem formation as growth slows.
141. In a typical dicot root, the vascular bundles (xylem poles) are usually described as “few” because they commonly range from:
ⓐ. 2 to 6 poles (diarch to hexarch)
ⓑ. 8 to 20 poles (polyarch)
ⓒ. Exactly 1 pole (monarch)
ⓓ. Exactly 12 poles (dodecarch)
Correct Answer: 2 to 6 poles (diarch to hexarch)
Explanation: Dicot roots generally show a limited number of xylem poles, commonly diarch, triarch, tetrarch, pentarch, or hexarch, which is why they are described as having “few” vascular bundles. This “pole number” refers to how many discrete protoxylem points (xylem arms) appear in transverse section. The pattern reflects typical primary root organization where xylem and phloem alternate radially and the xylem does not break into numerous small bundles. Very high pole numbers (polyarch) are more typical of many monocot roots. Hence, “few bundles” in dicot roots commonly means 2 to 6 poles.
142. While examining a root cross-section, you count four distinct protoxylem points arranged in a star-like pattern. This root would be classified as:
ⓐ. Diarch
ⓑ. Tetrarch
ⓒ. Hexarch
ⓓ. Polyarch
Correct Answer: Tetrarch
Explanation: The terms diarch, triarch, tetrarch, etc., describe the number of xylem poles (protoxylem points) visible in a transverse section of a root. If four protoxylem points are present, the condition is termed tetrarch. In dicot roots, tetrarch arrangement is a common example of “few” bundles because the xylem poles remain limited in number and form a clear radial pattern. This classification is based strictly on counting protoxylem points, not on the thickness of xylem or presence of pith. Therefore, four protoxylem points indicate a tetrarch root.
143. Which statement best explains the phrase “few vascular bundles” in dicot root anatomy?
ⓐ. Xylem and phloem are absent, so bundles are few
ⓑ. Vascular tissue forms many scattered bundles throughout cortex
ⓒ. The number of xylem poles is limited (commonly 2–6), with radial arrangement of xylem and phloem
ⓓ. Vascular bundles occur only in older roots after secondary growth begins
Correct Answer: The number of xylem poles is limited (commonly 2–6), with radial arrangement of xylem and phloem
Explanation: In dicot roots, “few bundles” refers to the limited number of xylem poles formed during primary growth, typically between two and six. These poles appear as distinct xylem arms in transverse section, with phloem strands alternating between them on separate radii. This radial organization is a hallmark of roots and differs from stems where xylem and phloem are conjoint in the same bundle. The phrase does not mean absence of vascular tissue or that bundles are scattered through the cortex. It also applies to primary anatomy, not only to older roots. Hence, limited xylem poles (commonly 2–6) in a radial pattern best explains “few vascular bundles.”
144. A root shows many xylem poles (e.g., more than 8) arranged around a large central pith. This condition is best described as:
ⓐ. Diarch, typical dicot root
ⓑ. Tetrarch, typical dicot root
ⓒ. Pentarch, typical dicot root
ⓓ. Polyarch, more typical of monocot root
Correct Answer: Polyarch, more typical of monocot root
Explanation: Polyarch refers to a root condition where the number of xylem poles is high, commonly more than eight, forming numerous alternating xylem and phloem strands. This pattern is more typical of monocot roots, which often also show a prominent central pith in primary structure. In contrast, dicot roots usually have fewer poles (2–6) and often show a smaller or inconspicuous pith. Therefore, a root with many poles arranged around a large pith fits the polyarch description. This is a standard diagnostic feature used in dicot-versus-monocot root identification. Hence, the correct classification is polyarch, more typical of monocot roots.
145. Which combination most strongly supports that a root is a dicot root with “few bundles”?
ⓐ. Radial xylem–phloem with 2–6 xylem poles and exarch xylem
ⓑ. Scattered vascular bundles with no endodermis and endarch xylem
ⓒ. Conjoint collateral bundles in a ring with a large pith and endarch xylem
ⓓ. Many xylem poles with a large central pith and closed bundles
Correct Answer: Radial xylem–phloem with 2–6 xylem poles and exarch xylem
Explanation: A dicot root typically shows radial arrangement of vascular tissues, where xylem and phloem alternate on different radii, and the xylem maturation is exarch. The “few bundles” feature is captured by having a limited number of xylem poles, commonly 2–6, forming a star-like xylem core in many cases. This combination is used as a reliable diagnostic set for dicot root anatomy in primary growth. Scattered bundles and endarch xylem are characteristic of stem patterns, not roots. A large pith with many poles suggests monocot root features. Therefore, radial xylem–phloem with 2–6 poles and exarch xylem most strongly supports a dicot root with “few bundles.”
146. A student counts three xylem poles in a root section and calls it “polyarch.” What is the correct interpretation?
ⓐ. Three poles means polyarch because any number above two is polyarch
ⓑ. Three poles means triarch, which still falls under “few bundles” typical of dicot roots
ⓒ. Three poles means tetrarch because the stele is star-shaped
ⓓ. Three poles means monarch because only one xylem is functional
Correct Answer: Three poles means triarch, which still falls under “few bundles” typical of dicot roots
Explanation: The pole number in roots is named directly from the count: three xylem poles indicate a triarch condition. “Polyarch” is reserved for many poles, typically more than about eight, and is not used for three. In dicot roots, triarch is considered part of the “few bundles” range (commonly 2–6). The shape of the stele can be star-like even with different pole numbers, but naming depends on counting protoxylem points, not on general appearance. Thus, the correct correction is triarch, consistent with “few bundles.” Hence, three poles indicate a triarch dicot-type pattern.
147. In a dicot root described as “few-bundled,” the phloem is typically located:
ⓐ. In patches alternating between xylem poles on separate radii
ⓑ. As a continuous ring completely surrounding xylem with no breaks
ⓒ. Only at the center of the stele, enclosed by xylem
ⓓ. Scattered randomly in the cortex, unrelated to xylem position
Correct Answer: In patches alternating between xylem poles on separate radii
Explanation: In roots, vascular tissues are arranged radially rather than conjointly, so xylem and phloem occupy different radii. In a dicot root with few xylem poles, phloem typically occurs in discrete patches between adjacent xylem arms, alternating around the stele. This alternating arrangement is a standard feature of primary root anatomy and aligns with the “few bundles” concept because the number of repeating xylem–phloem units is limited. A continuous phloem ring is more characteristic of certain stem patterns, not typical primary roots. Random phloem distribution in cortex is not a root vascular plan. Therefore, phloem alternating between xylem poles best describes its location in a few-bundled dicot root.
148. Why is “few xylem poles” a useful clue for identifying dicot roots in basic anatomy questions?
ⓐ. Because it guarantees the absence of endodermis in dicot roots
ⓑ. Because dicot roots always have exactly two poles in every species
ⓒ. Because limited pole number (2–6) commonly contrasts with many-poled (polyarch) patterns in monocot roots
ⓓ. Because it proves the presence of vessels and absence of tracheids in roots
Correct Answer: Because limited pole number (2–6) commonly contrasts with many-poled (polyarch) patterns in monocot roots
Explanation: In many introductory anatomy comparisons, dicot roots are described as having a limited number of xylem poles (often 2–6), while monocot roots frequently show a higher number of poles (polyarch). This contrast provides a quick identification cue when viewing transverse sections, especially when combined with other root features like radial bundles and exarch xylem. It does not imply that dicot roots lack endodermis, since endodermis is a key root feature in both groups. It also does not fix the pole number at exactly two, because dicot roots can be triarch, tetrarch, and so on. Conduit types (vessels vs tracheids) are not determined solely by pole count. Hence, “few poles” is useful because it contrasts with the many-poled pattern commonly seen in monocot roots.
149. A transverse section shows a small or inconspicuous pith and 4–5 xylem poles. This finding is most consistent with:
ⓐ. Monocot root with polyarch xylem
ⓑ. Dicot root with few bundles (tetrarch/pentarch range)
ⓒ. Dicot stem with ring of conjoint bundles
ⓓ. Monocot stem with scattered bundles
Correct Answer: Dicot root with few bundles (tetrarch/pentarch range)
Explanation: A dicot root commonly shows a limited number of xylem poles and often has a small or less prominent pith compared to many monocot roots. When the pole number is 4–5, the root falls into tetrarch/pentarch categories, which are within the “few bundles” range. This combination supports a dicot root identification rather than a monocot root, which more often shows polyarch xylem and a larger central pith. Stem sections are identified by conjoint vascular bundles (xylem and phloem together) arranged in a ring (dicot stem) or scattered (monocot stem), not by radial pole counts. Therefore, small pith with 4–5 poles is most consistent with a dicot root with few bundles.
150. Which statement about “few vascular bundles” in dicot roots is most accurate in exam terms?
ⓐ. It refers to fewer stomata on roots compared with stems
ⓑ. It refers to fewer cortex layers compared with monocot roots
ⓒ. It refers to fewer pericycle cells compared with monocot roots
ⓓ. It refers to fewer xylem poles (commonly 2–6) visible in transverse section
Correct Answer: It refers to fewer xylem poles (commonly 2–6) visible in transverse section
Explanation: In root anatomy, the term “few vascular bundles” is used as shorthand for a limited number of xylem poles in the primary stele. This is assessed by counting distinct protoxylem points in a transverse section, which in dicot roots commonly falls between two and six. The phrasing does not relate to stomata (roots generally do not use stomata for regulation), nor does it directly count cortex layers or pericycle cell number. It is specifically about the vascular pattern within the stele, where xylem and phloem alternate radially. This concept is frequently used in dicot-versus-monocot comparisons. Hence, “few vascular bundles” most accurately refers to fewer xylem poles (commonly 2–6).
151. In a typical dicot root, the pith is most commonly described as:
ⓐ. Large and well-developed with many parenchyma cells
ⓑ. Small and inconspicuous or sometimes absent
ⓒ. Always replaced by a hollow air cavity (aerenchyma)
ⓓ. Composed mainly of sclerenchyma fibres for mechanical strength
Correct Answer: Small and inconspicuous or sometimes absent
Explanation: In dicot roots, the central region is often dominated by xylem, which forms a star-shaped core, leaving little space for a prominent pith. As a result, the pith is usually small, poorly developed, or may even appear absent in many transverse sections. This is a useful diagnostic feature when comparing dicot roots with monocot roots, where the pith is often large and conspicuous. The tissue present, if any, is typically parenchymatous, but its extent is limited. The “small/absent” description reflects the vascular architecture rather than a special air cavity or heavy sclerenchyma. Therefore, dicot roots commonly have a small and inconspicuous or sometimes absent pith.
152. Which anatomical arrangement most directly explains why pith tends to be small in dicot roots?
ⓐ. The epidermis forms a thick cuticle that pushes pith inward
ⓑ. The xylem occupies the central region of the stele as a solid core, leaving little room for pith
ⓒ. The cortex becomes lignified and replaces the pith
ⓓ. The endodermis expands inward and converts into pith tissue
Correct Answer: The xylem occupies the central region of the stele as a solid core, leaving little room for pith
Explanation: In dicot roots, the primary xylem commonly forms a central, star-like or solid core within the stele. Because this xylem mass occupies much of the center, there is limited space left for a distinct central pith region. Any pith present is therefore reduced to a small, inconspicuous area, and in some roots it may not be clearly demarcated. This relationship is structural: the vascular arrangement determines the space available for pith. It is not caused by cuticle formation, lignification of cortex, or conversion of endodermis. Hence, central occupation by xylem best explains the small pith in dicot roots.
153. A root cross-section shows radial xylem and phloem with a very large, distinct pith. This feature is more typical of:
ⓐ. Dicot root
ⓑ. Dicot leaf midrib
ⓒ. Dicot stem
ⓓ. Monocot root
Correct Answer: Monocot root
Explanation: A large, well-developed pith in the center of the stele is commonly associated with monocot roots. Monocot roots often have many xylem poles arranged around a conspicuous central pith, creating a ring-like vascular pattern with a prominent parenchymatous pith. In contrast, dicot roots often have a smaller or inconspicuous pith because xylem occupies much of the center. Dicot stems are identified by conjoint bundles arranged in a ring, not by a root-like radial pattern with a large pith. Therefore, a root section with radial tissues and a large pith is more typical of a monocot root.
154. In a typical dicot root with small/absent pith, the central region is most likely occupied by:
ⓐ. Aerenchyma with large air spaces for buoyancy
ⓑ. A thick cork layer formed by phellogen
ⓒ. Primary xylem forming a central mass
ⓓ. Companion cells arranged around sieve plates
Correct Answer: Primary xylem forming a central mass
Explanation: The key reason dicot roots often show a small or absent pith is that primary xylem commonly occupies the central region as a compact mass. This xylem arrangement reduces the space available for a central parenchymatous pith. The tissue is specialized for water and mineral conduction and structural support, so it forms a strong core within the stele. Aerenchyma is an adaptation in some aquatic or marsh plants and is not the typical “central filler” in dicot root stele. Cork is a protective tissue of older organs and is not the primary central component of young roots. Companion cells are phloem-associated and not central in roots. Therefore, primary xylem most likely occupies the central region in such dicot roots.
155. A student claims: “Pith is absent in all dicot roots without exception.” What is the most accurate correction?
ⓐ. Pith is always large in dicot roots, so the claim is reversed
ⓑ. Pith can be small and inconspicuous and may appear absent, but it is not universally absent in every dicot root
ⓒ. Pith is made of xylem, so it cannot be absent
ⓓ. Pith is absent only because the cortex replaces it in dicot roots
Correct Answer: Pith can be small and inconspicuous and may appear absent, but it is not universally absent in every dicot root
Explanation: In dicot roots, pith is typically described as small or inconspicuous, and in many sections it may look absent because the central xylem is prominent. However, “absent” is not an absolute rule for every dicot species or every root segment; some dicot roots can show a small pith region depending on species, developmental stage, and the exact arrangement of xylem. The correct exam-safe idea is that pith is usually reduced compared with monocot roots. It is also important not to confuse pith with xylem; pith is parenchymatous ground tissue when present. Therefore, the accurate correction is that pith may appear absent but is not universally absent in all dicot roots.
156. Which comparison best supports “pith small/absent” as a dicot root feature in dicot–monocot root questions?
ⓐ. Dicot root: small/absent pith; Monocot root: large, well-developed pith
ⓑ. Dicot root: large pith; Monocot root: no pith at all
ⓒ. Dicot root: pith replaced by stomata; Monocot root: pith replaced by cuticle
ⓓ. Dicot root: pith always lignified; Monocot root: pith always chlorenchymatous
Correct Answer: Dicot root: small/absent pith; Monocot root: large, well-developed pith
Explanation: A standard anatomical distinction taught in dicot versus monocot root comparisons is the relative development of pith. Dicot roots commonly show a reduced pith because the central region is largely occupied by xylem, while monocot roots often display a large, conspicuous parenchymatous pith at the center. This feature is used alongside other traits like number of xylem poles and secondary growth tendencies to identify sections in exams. The other options introduce incorrect structures (stomata, cuticle) as pith replacements or make unrealistic claims about lignification and chlorenchyma as defining pith traits. Thus, the most accurate comparison is small/absent pith in dicot roots versus large pith in monocot roots. Hence, option A is correct.
157. In a dicot root cross-section, which observation would most likely indicate that the pith is inconspicuous?
ⓐ. A distinct central region of large parenchyma clearly separated from xylem
ⓑ. A central ring of phloem encircling xylem completely
ⓒ. A central cavity filled with air spaces surrounded by cortex
ⓓ. A central region dominated by xylem with little or no parenchymatous ground tissue in the middle
Correct Answer: A central region dominated by xylem with little or no parenchymatous ground tissue in the middle
Explanation: An inconspicuous pith in dicot roots means the central parenchymatous region is reduced or not clearly demarcated. This is most evident when the xylem occupies the center strongly, leaving little ground tissue at the core. In many dicot roots, the star-shaped xylem can extend nearly to the center, making any pith region very small or seemingly absent. A distinct central parenchyma region would instead indicate a prominent pith, more typical of many monocot roots. Air-filled cavities are special adaptations and are not standard indicators of dicot root pith condition. A phloem ring around xylem is not the typical radial root pattern. Therefore, a center dominated by xylem with minimal ground tissue best indicates an inconspicuous pith.
158. Which internal tissue would be most directly affected if a dicot root had an unusually enlarged pith compared with the typical condition?
ⓐ. The relative central dominance of xylem within the stele would be reduced
ⓑ. The cuticle thickness on the root surface would increase
ⓒ. Stomatal density on the root epidermis would increase
ⓓ. The presence of root cap would be eliminated
Correct Answer: The relative central dominance of xylem within the stele would be reduced
Explanation: In typical dicot roots, the pith is small because xylem occupies much of the center. If the pith becomes unusually enlarged, it implies that the central space is increasingly occupied by parenchymatous ground tissue rather than xylem. This would reduce the relative dominance or compactness of xylem at the center of the stele, altering the common dicot pattern. Cuticle thickness is not the primary variable controlling stele architecture in roots, and stomata are not typical root structures. The root cap is a separate protective structure at the tip and is not directly determined by pith size in mature cross-sections. Therefore, an enlarged pith would most directly reduce the central dominance of xylem.
159. Which statement best fits the tissue identity of pith (when present) in dicot roots?
ⓐ. Pith is mainly composed of living parenchyma cells used for storage and internal support
ⓑ. Pith is mainly composed of vessel elements for water conduction
ⓒ. Pith is mainly composed of sieve tube elements for sugar transport
ⓓ. Pith is mainly composed of sclerenchyma fibres with thick lignified walls
Correct Answer: Pith is mainly composed of living parenchyma cells used for storage and internal support
Explanation: Pith, when present, is a ground tissue region typically made up of living parenchyma cells. These cells often function in storage of reserve materials and can contribute to internal tissue packing and limited support through turgor. They are not specialized conducting elements like vessels or sieve tubes, and they are not primarily thick-walled sclerenchyma fibres. In dicot roots, the pith is often reduced, but if present, its basic histological identity remains parenchymatous. This helps distinguish pith from the vascular tissues that surround or replace it in different organs. Therefore, pith is mainly living parenchyma used for storage and internal support.
160. A root section shows exarch xylem with 4 xylem poles and an inconspicuous pith. This combination most strongly indicates:
ⓐ. Dicot stem anatomy
ⓑ. Monocot stem anatomy
ⓒ. Dicot root anatomy
ⓓ. Monocot leaf anatomy
Correct Answer: Dicot root anatomy
Explanation: Exarch xylem is a classic root feature, indicating protoxylem toward the periphery and metaxylem toward the center. A limited number of xylem poles such as four (tetrarch) fits the “few bundles” pattern often described for dicot roots. An inconspicuous or small pith further supports the dicot root identification, since monocot roots typically show a large central pith and often polyarch xylem. Stem anatomy would show conjoint bundles rather than a radial xylem–phloem arrangement associated with roots. The combined presence of exarch xylem, few poles, and small pith forms a strong diagnostic set. Therefore, this section most strongly indicates dicot root anatomy.
161. In a monocot root, the term “polyarch” most directly refers to:
ⓐ. Presence of many xylem poles arranged radially around the pith
ⓑ. Presence of one large central xylem bundle with phloem outside
ⓒ. Presence of vascular bundles scattered throughout the cortex
ⓓ. Presence of xylem in concentric rings surrounding phloem
Correct Answer: Presence of many xylem poles arranged radially around the pith
Explanation: Polyarch is a descriptive term for roots in which the number of xylem poles (protoxylem points) is high, typically more than about eight. In monocot roots, many alternating xylem and phloem strands are arranged radially, commonly around a prominent central pith. This creates a ring-like appearance of many vascular units in transverse section. The term does not mean scattered bundles in cortex, and it does not describe concentric xylem rings around phloem. It is specifically about “many xylem poles” in a radial root stele. Therefore, polyarch in a monocot root refers to many xylem poles arranged radially around the pith.
162. A root cross-section shows 12 distinct protoxylem points. This vascular condition is best termed:
ⓐ. Tetrarch
ⓑ. Hexarch
ⓒ. Diarch
ⓓ. Polyarch
Correct Answer: Polyarch
Explanation: Root xylem pole number is named according to how many protoxylem points are visible in transverse section. Low numbers such as 2, 4, or 6 are termed diarch, tetrarch, or hexarch, respectively. When the number becomes high, commonly above eight, the root is described as polyarch. A count of 12 protoxylem points clearly falls into the “many poles” category. This polyarch condition is commonly associated with monocot roots and is often accompanied by a large pith. Hence, 12 protoxylem points indicate a polyarch root.
163. Which combination most strongly supports “monocot root with polyarch xylem” in an exam identification question?
ⓐ. Conjoint collateral bundles in a ring with endarch xylem and large pith
ⓑ. Radial bundles with many xylem poles and a prominent central pith
ⓒ. Scattered bundles in ground tissue with no endodermis and no pericycle
ⓓ. Few xylem poles with star-shaped xylem core and inconspicuous pith
Correct Answer: Radial bundles with many xylem poles and a prominent central pith
Explanation: Monocot roots typically show radial arrangement of xylem and phloem and often have many xylem poles, termed polyarch. A prominent central pith is also a common accompanying feature in monocot roots, producing a clear separation between the many vascular strands and the center. Conjoint collateral bundles in a ring are characteristic of dicot stems, not roots. Scattered bundles are typical of monocot stems, and roots generally show a distinct endodermis and pericycle. Few poles with a star-shaped xylem core suggests a dicot root pattern. Therefore, radial bundles with many poles and a prominent pith best identifies a monocot root with polyarch xylem.
164. In a polyarch monocot root, where is the protoxylem most likely located relative to the stele?
ⓐ. Toward the periphery of the stele, consistent with exarch maturation
ⓑ. Strictly at the center, surrounding a hollow cavity
ⓒ. Inside the cortex, outside the endodermis
ⓓ. Only within the pith, never near vascular strands
Correct Answer: Toward the periphery of the stele, consistent with exarch maturation
Explanation: Roots typically show exarch xylem maturation, meaning protoxylem is positioned more peripherally and metaxylem is more central. This applies to both dicot and monocot roots, including polyarch monocot roots. In a polyarch condition, many protoxylem points appear toward the outer side of the stele, usually near the endodermis, with larger metaxylem elements located more inward. Protoxylem does not lie in the cortex outside the endodermis because vascular tissues are confined within the stele. It also does not occupy only the pith. Hence, protoxylem is toward the periphery in a polyarch monocot root, consistent with exarch maturation.
165. Which statement best explains why monocot roots are more likely to show polyarch xylem than dicot roots?
ⓐ. Monocot roots typically form many xylem poles as part of their primary vascular organization, increasing radial conduction capacity
ⓑ. Monocot roots lack endodermis, so xylem spreads into the cortex as many bundles
ⓒ. Monocot roots convert phloem into extra xylem poles during secondary growth
ⓓ. Monocot roots always have fewer vascular bundles because they lack cambium
Correct Answer: Monocot roots typically form many xylem poles as part of their primary vascular organization, increasing radial conduction capacity
Explanation: In monocot roots, the primary stele commonly differentiates into many alternating xylem and phloem strands, giving rise to a polyarch condition. This increases the number of conducting points distributed around the stele and is a consistent anatomical trait used for identification. The endodermis is present and well-defined in monocot roots, so xylem does not spread into the cortex. Polyarch is not created by converting phloem into xylem during secondary growth; in fact, most monocots show limited typical secondary growth in roots. The key explanation is the inherent primary vascular pattern of monocot roots. Therefore, monocot roots show polyarch xylem because many poles form during primary organization, increasing radial conduction capacity.
166. A student counts 10 xylem poles in a root and still labels it “hexarch.” What is the correct classification?
ⓐ. Hexarch, because any number above six is still called hexarch
ⓑ. Polyarch, because the pole number is high (many poles)
ⓒ. Tetrarch, because the arrangement is radial
ⓓ. Diarch, because only two poles conduct actively at a time
Correct Answer: Polyarch, because the pole number is high (many poles)
Explanation: Hexarch specifically refers to a root with six xylem poles, not a general label for all higher numbers. When the number of poles becomes high—commonly more than about eight—the correct term used is polyarch. A count of 10 xylem poles clearly falls in the polyarch range. The fact that the arrangement is radial does not determine whether it is tetrarch; tetrarch is strictly four poles. “Two poles conduct actively at a time” is not a valid basis for naming pole number. Hence, a 10-pole root should be classified as polyarch.
167. Which observation is most consistent with the vascular appearance of a polyarch monocot root in transverse section?
ⓐ. A star-shaped xylem core with 3–5 arms occupying the center
ⓑ. Scattered closed vascular bundles throughout the cortex with no clear stele boundary
ⓒ. One large vascular bundle near the center with no alternation of phloem
ⓓ. Many small xylem groups arranged in a ring, alternating with phloem around a large pith
Correct Answer: Many small xylem groups arranged in a ring, alternating with phloem around a large pith
Explanation: In a polyarch monocot root, numerous xylem poles appear as many groups arranged radially, often forming a ring-like pattern. Phloem strands occur between xylem poles on alternate radii, and a large central pith is commonly present, producing a clear core of parenchyma. This contrasts with dicot roots, where xylem often forms a star-shaped central core with fewer arms and an inconspicuous pith. The vascular tissues in roots remain within a defined stele and do not appear as scattered bundles in the cortex like a monocot stem. Therefore, the ring of many xylem groups alternating with phloem around a large pith best matches a polyarch monocot root.
168. In a monocot root with polyarch xylem, what is the most accurate role of the central pith?
ⓐ. It is primarily a conducting tissue for water flow under tension
ⓑ. It mainly provides storage and internal packing as parenchyma, while conduction occurs in xylem and phloem
ⓒ. It forms the endodermal barrier controlling apoplastic movement
ⓓ. It is composed of dead sclerenchyma fibres providing the main support
Correct Answer: It mainly provides storage and internal packing as parenchyma, while conduction occurs in xylem and phloem
Explanation: The central pith in monocot roots is typically made of living parenchyma cells that provide storage, internal packing, and sometimes limited support through turgor. Conduction of water and minerals occurs through xylem, while translocation of organic solutes occurs through phloem, both arranged radially around the pith. The pith itself is not a primary conducting tissue and does not form the endodermal barrier; endodermis is a distinct layer at the boundary of cortex and stele. Pith is also not typically dead sclerenchyma in roots. Thus, the pith’s main function is storage and internal tissue filling rather than conduction. Therefore, the central pith mainly serves storage/packing as parenchyma.
169. Which statement correctly links “polyarch” with a practical counting approach in a root section?
ⓐ. Polyarch is identified by counting cambium layers in the pericycle
ⓑ. Polyarch is identified by counting the number of cortical layers outside endodermis
ⓒ. Polyarch is identified by counting the number of stomata on the root epidermis
ⓓ. Polyarch is identified by counting the number of protoxylem points around the stele
Correct Answer: Polyarch is identified by counting the number of protoxylem points (xylem poles) around the stele
Explanation: The term polyarch is based on the number of xylem poles, which correspond to protoxylem points visible in transverse section of the root. By counting these protoxylem groups around the stele, one can classify the root as diarch, tetrarch, hexarch, or polyarch when the number is high. This method is widely used in practical microscopy and exam identification questions because the protoxylem points are relatively distinct. Cambium layers, stomata, and cortical layer counts are unrelated to the definition of polyarch. The defining criterion remains the high number of xylem poles. Therefore, polyarch is identified by counting protoxylem points around the stele.
170. A root shows radial bundles, exarch xylem, a large pith, and 14 xylem poles. This set of features most strongly indicates:
ⓐ. Dicot root with few bundles and small pith
ⓑ. Monocot root with polyarch xylem
ⓒ. Dicot stem with ring of conjoint bundles
ⓓ. Monocot stem with scattered vascular bundles
Correct Answer: Monocot root with polyarch xylem
Explanation: Radial arrangement of xylem and phloem and exarch maturation are characteristic features of roots. A large, conspicuous pith combined with a high number of xylem poles (14) strongly fits the polyarch pattern commonly seen in monocot roots. Dicot roots usually have fewer poles and often a small or inconspicuous pith, while stems show conjoint bundles (ringed in dicots or scattered in monocots) rather than radial root pattern. The combination of root traits plus many poles and large pith forms a classic monocot root identification set. Therefore, these features most strongly indicate a monocot root with polyarch xylem.
171. In a typical monocot root, the pith is most accurately described as:
ⓐ. Large, well-developed and mainly parenchymatous
ⓑ. Small, inconspicuous, and often absent
ⓒ. Composed mainly of vessels and tracheids for conduction
ⓓ. A lignified sclerenchyma mass that replaces xylem
Correct Answer: Large, well-developed and mainly parenchymatous
Explanation: Monocot roots commonly have a prominent central pith that is clearly visible in transverse section. This pith is typically made up of living parenchyma cells that serve storage and internal packing functions rather than conduction. The conducting tissues (xylem and phloem) are arranged radially around this pith, often with many poles. This contrasts with many dicot roots where the xylem occupies more central space, making pith small or inconspicuous. The pith is not a lignified replacement for xylem and is not mainly composed of tracheary elements. Therefore, monocot roots characteristically show a large, well-developed parenchymatous pith.
172. Which anatomical pattern most directly explains why pith is large in monocot roots?
ⓐ. Xylem forms a solid star-shaped core that fills the center of the stele
ⓑ. Endodermis disappears, so cortex becomes the pith
ⓒ. Cork tissues expand inward and convert the center into pith
ⓓ. Vascular tissues form a ring with many poles, leaving a broad central parenchymatous region
Correct Answer: Vascular tissues form a ring with many poles, leaving a broad central parenchymatous region
Explanation: In monocot roots, xylem and phloem occur in many radial strands (often polyarch), commonly arranged in a ring-like pattern within the stele. This arrangement leaves a large central space that is occupied by parenchyma, forming a conspicuous pith. Unlike many dicot roots, the xylem does not dominate the center as a compact star-shaped core, so the pith remains broad. The pith is not formed by cork growth and does not result from loss of endodermis; endodermis remains a distinct boundary layer in roots. The large pith is therefore a consequence of the vascular arrangement and space allocation within the stele. Hence, ring-like vascular distribution with many poles leaves a large central parenchymatous pith.
173. A root section shows many xylem poles and a prominent central pith. Which identification is most consistent?
ⓐ. Dicot root with tetrarch xylem and small pith
ⓑ. Dicot stem with ring of vascular bundles
ⓒ. Monocot root with polyarch xylem and large pith
ⓓ. Monocot stem with scattered vascular bundles and no pith
Correct Answer: Monocot root with polyarch xylem and large pith
Explanation: Many xylem poles (polyarch condition) plus a large central pith are classic diagnostic features of monocot roots in transverse section. Roots also show radial arrangement of xylem and phloem, distinguishing them from stems where bundles are conjoint and arranged differently. Dicot roots generally have fewer xylem poles and often a reduced pith because xylem occupies more central space. Monocot stems can have scattered vascular bundles, but they do not show the root-like radial pole pattern around a central pith. Therefore, the best match for a section with polyarch xylem and prominent pith is a monocot root. Hence, the correct identification is a monocot root with polyarch xylem and large pith.
174. The pith in a monocot root is mainly important for:
ⓐ. Bulk conduction of water under tension from root to shoot
ⓑ. Storage and internal tissue packing using living parenchyma cells
ⓒ. Opening and closing stomata to regulate water loss
ⓓ. Formation of Casparian strips to block apoplastic movement
Correct Answer: Storage and internal tissue packing using living parenchyma cells
Explanation: Pith in monocot roots is primarily composed of living parenchyma cells, which commonly function in storage of reserves and in filling the central space of the stele. Conduction of water and minerals occurs mainly through xylem, and translocation of sugars occurs through phloem, not through pith. Stomata are epidermal structures of aerial organs and are not part of root pith function. Casparian strips belong to endodermal cells at the cortex–stele boundary, not to pith cells at the center. The large pith provides internal packing and can contribute to organ volume and storage capacity. Therefore, the pith’s main role in monocot roots is storage and internal tissue packing.
175. Which statement best corrects the claim: “Large pith is a defining feature of all roots”?
ⓐ. Large pith is typical of many monocot roots, whereas many dicot roots show small or inconspicuous pith
ⓑ. Large pith is found only in dicot roots and never in monocot roots
ⓒ. Large pith is always present because xylem never occupies the center in any root
ⓓ. Large pith appears only after secondary growth starts in roots
Correct Answer: Large pith is typical of many monocot roots, whereas many dicot roots show small or inconspicuous pith
Explanation: Root pith size varies with the type of root and its vascular arrangement. Many monocot roots characteristically have a large, well-developed pith because vascular tissues are arranged around a central parenchymatous region. In contrast, many dicot roots have a small or inconspicuous pith because primary xylem often occupies the center more strongly. Therefore, it is inaccurate to state that all roots have large pith as a defining rule. The distinction is commonly used in monocot-versus-dicot identification questions. Hence, large pith is typical of many monocot roots, while many dicot roots show reduced pith.
176. A transverse section of root shows a broad central parenchymatous region and multiple alternating xylem and phloem strands around it. This central parenchymatous region is the:
ⓐ. Cortex
ⓑ. Endodermis
ⓒ. Pericycle
ⓓ. Pith
Correct Answer: Pith
Explanation: In root anatomy, the pith refers to the central ground tissue region within the stele, usually parenchymatous when present. In many monocot roots, vascular tissues occur as multiple alternating xylem and phloem strands arranged around a large central pith. The cortex lies outside the endodermis and forms the bulk of tissue between epidermis and stele, so it is not the central stele region. Endodermis is a boundary layer, and pericycle is a thin layer just inside endodermis, neither forming a broad central region. Therefore, the broad central parenchymatous region within the stele is the pith. Hence, the correct term is pith.
177. Which comparison most reliably uses pith size to distinguish monocot and dicot roots in basic anatomy?
ⓐ. Monocot root: small pith; Dicot root: large pith
ⓑ. Monocot root: large pith; Dicot root: small/inconspicuous pith
ⓒ. Monocot root: no pith; Dicot root: no pith
ⓓ. Monocot root: lignified pith; Dicot root: chlorenchymatous pith
Correct Answer: Monocot root: large pith; Dicot root: small/inconspicuous pith
Explanation: A common exam-level distinction is that monocot roots generally show a prominent central pith, while dicot roots often show a reduced or inconspicuous pith due to more centrally placed xylem. This difference is easy to observe in transverse sections when combined with other root traits such as radial vascular arrangement and xylem pole number. The opposite comparison is not generally accurate, and both groups can show variations, but the typical pattern remains as stated. Claims about lignified or chlorenchymatous pith are not standard distinguishing criteria in roots. Therefore, the most reliable pith-based comparison is large pith in monocot roots versus small/inconspicuous pith in dicot roots.
178. In a monocot root with large pith, which vascular pattern is most commonly associated with this feature?
ⓐ. Few xylem poles (2–4) forming a solid central star
ⓑ. Many xylem poles (polyarch) arranged around the pith
ⓒ. Conjoint vascular bundles arranged in a ring
ⓓ. Scattered vascular bundles without a clear endodermis
Correct Answer: Many xylem poles (polyarch) arranged around the pith
Explanation: Large pith in monocot roots is commonly accompanied by polyarch xylem, where many xylem poles are arranged radially around the central pith. This arrangement produces a ring-like distribution of vascular tissues, leaving a substantial central region for parenchymatous pith. Few-pole, star-shaped xylem cores are more typical of many dicot roots and tend to reduce pith size. Conjoint bundles arranged in a ring describe stem anatomy rather than root anatomy. Scattered bundles are typical of monocot stems, and roots generally retain a distinct endodermis. Hence, polyarch xylem arranged around the pith is most commonly associated with large pith in monocot roots.
179. A student sees a large pith in a root and concludes it must be a dicot root. Which reasoning best corrects this?
ⓐ. Large pith more commonly indicates a monocot root, especially when xylem shows many poles
ⓑ. Large pith indicates a dicot stem, not a root
ⓒ. Large pith always means secondary growth has occurred, so it cannot be monocot
ⓓ. Large pith means phloem is absent, which is typical of dicot roots
Correct Answer: Large pith more commonly indicates a monocot root, especially when xylem shows many poles
Explanation: In basic anatomy comparisons, a prominent central pith is more commonly associated with monocot roots than dicot roots. Monocot roots often show many xylem poles arranged around a large parenchymatous pith, whereas many dicot roots have a smaller or inconspicuous pith because xylem occupies more central space. Therefore, using large pith alone as a “dicot marker” is a misconception; it must be interpreted with other features like xylem pole number and overall vascular arrangement. Secondary growth is not a prerequisite for a large pith in monocot roots. Phloem is present in both root types as alternating strands. Hence, large pith more commonly indicates a monocot root, especially alongside polyarch xylem.
180. Which statement best links large pith with the overall tissue organization of a monocot root?
ⓐ. Large pith forms because epidermis invaginates into the stele during development
ⓑ. Large pith is the same as endodermis and is defined by Casparian strips
ⓒ. Large pith represents expanded central ground tissue within the stele, while vascular strands occupy a peripheral ring
ⓓ. Large pith results from conversion of xylem into parenchyma during maturation
Correct Answer: Large pith represents expanded central ground tissue within the stele, while vascular strands occupy a peripheral ring
Explanation: In monocot roots, the stele often includes a broad central region of ground tissue that differentiates as parenchymatous pith. The vascular tissues—xylem and phloem—are arranged as multiple radial strands that together occupy a more peripheral ring within the stele, leaving the center free for pith development. This arrangement is structural and developmental, reflecting how tissues are allocated during primary growth. The pith is not formed by epidermal invagination and is not the endodermis, which is a boundary layer with Casparian strips. It also does not arise from converting xylem into parenchyma as a standard maturation process. Therefore, large pith reflects expanded central ground tissue within the stele with vascular strands forming a peripheral ring.
181. In a typical dicot stem, vascular bundles are arranged:
ⓐ. In a scattered pattern throughout the ground tissue
ⓑ. In a single central bundle surrounded by ground tissue
ⓒ. As a central vascular core surrounded by a thick cortex
ⓓ. In a ring around the central pith
Correct Answer: In a ring around the central pith
Explanation: Dicot stems typically have vascular bundles arranged in a ring around a central pith, forming a characteristic pattern in transverse section. The vascular bundles consist of xylem and phloem, with the xylem facing inward and the phloem facing outward. This arrangement allows for the support of the plant as it grows in height. In contrast, monocot stems typically have scattered vascular bundles, and the pith is less prominent. The ringed arrangement of vascular bundles is a defining feature of dicot stems, differentiating them from monocots, which often exhibit a more scattered pattern.
182. Which of the following is a characteristic feature of a dicot stem with vascular bundles arranged in a ring?
ⓐ. The presence of large parenchymatous pith surrounded by vascular bundles
ⓑ. Vascular bundles scattered randomly within the stem without any particular arrangement
ⓒ. A single vascular bundle in the center of the stem surrounded by ground tissue
ⓓ. A complete absence of vascular tissue in the central region
Correct Answer: The presence of large parenchymatous pith surrounded by vascular bundles
Explanation: In dicot stems, the vascular bundles are arranged in a ring around a central parenchymatous pith. The pith is composed of living parenchyma cells and serves to store nutrients and water. The vascular bundles, consisting of both xylem and phloem, form the outer boundary of the stele and are responsible for transporting water, minerals, and nutrients. In contrast, monocot stems show scattered vascular bundles, and they do not have a prominent central pith. Hence, the characteristic feature of dicot stems is the presence of a large parenchymatous pith surrounded by the vascular bundles arranged in a ring.
183. The presence of vascular bundles in a ring in a dicot stem is most important for:
ⓐ. Increasing the efficiency of photosynthesis by facilitating light penetration
ⓑ. Providing structural support and allowing for secondary growth in the stem
ⓒ. Storing large amounts of water for drought resistance
ⓓ. Enhancing water conduction from the roots to the leaves
Correct Answer: Providing structural support and allowing for secondary growth in the stem
Explanation: The arrangement of vascular bundles in a ring in dicot stems provides structural support and enables the plant to undergo secondary growth. The ringed pattern allows for the formation of a cambium layer between the xylem and phloem in each vascular bundle, which can give rise to secondary xylem (wood) and secondary phloem during growth. This secondary growth increases the diameter of the stem, contributing to the plant’s ability to grow larger and become more rigid. While photosynthesis, water conduction, and storage are important, secondary growth driven by vascular bundles in a ring is the key function associated with this arrangement.
184. Which of the following best describes the vascular bundles in a dicot stem compared to a monocot stem?
ⓐ. Dicot stems have scattered vascular bundles, while monocot stems have a ring of vascular bundles
ⓑ. Dicot stems have a single central vascular bundle, while monocot stems have multiple bundles arranged in a ring
ⓒ. Dicot stems have vascular bundles arranged in a ring, while monocot stems have scattered vascular bundles
ⓓ. Dicot stems have vascular bundles only in the cortex, while monocot stems have them in the center
Correct Answer: Dicot stems have vascular bundles arranged in a ring, while monocot stems have scattered vascular bundles
Explanation: The vascular bundles in dicot stems are typically arranged in a ring around the central pith, with xylem facing inward and phloem facing outward. This arrangement allows for secondary growth and provides structural support. In monocot stems, however, the vascular bundles are scattered throughout the ground tissue, and they do not form a ring. This scattered arrangement prevents secondary growth and limits the plant’s ability to increase in girth. Hence, the key distinguishing feature is that dicot stems have vascular bundles arranged in a ring, while monocot stems have scattered vascular bundles.
185. The presence of a vascular bundle ring in dicot stems facilitates which of the following processes?
ⓐ. Secondary growth, which increases stem girth and allows for the formation of wood
ⓑ. Increased transpiration rates due to open stomata surrounding each vascular bundle
ⓒ. Enhanced gas exchange between the phloem and xylem within the vascular bundle
ⓓ. Decreased mechanical strength as the plant cannot grow in height
Correct Answer: Secondary growth, which increases stem girth and allows for the formation of wood
Explanation: The arrangement of vascular bundles in a ring in dicot stems allows for secondary growth. This growth occurs when the cambium, which forms between the xylem and phloem in each vascular bundle, divides and produces new xylem (wood) and phloem. This process increases the girth of the stem, allowing the plant to grow larger and stronger over time. This is characteristic of dicots, which can undergo significant secondary growth, unlike monocots, which typically lack this ability. Secondary growth is responsible for the formation of wood and is a critical process for structural support in woody plants.
186. In a dicot stem with vascular bundles arranged in a ring, which tissue forms the boundary between the xylem and phloem in each bundle?
ⓐ. Endodermis
ⓑ. Cambium
ⓒ. Cortex
ⓓ. Epidermis
Correct Answer: Cambium
Explanation: The cambium is the meristematic tissue that forms the boundary between the xylem and phloem in vascular bundles. In dicot stems, this layer of cambium allows for secondary growth by producing new xylem toward the interior and new phloem toward the exterior. This process enables the stem to increase in diameter, which is a defining characteristic of dicot stems compared to monocot stems. The cambium is crucial for the continued growth and development of the vascular tissues in woody plants. The endodermis, cortex, and epidermis are distinct layers of the root or stem, but they do not form the boundary between xylem and phloem in vascular bundles.
187. In a transverse section of a dicot stem, the vascular bundles are arranged in a circle. Which layer would be directly located outside the vascular bundles?
ⓐ. Epidermis
ⓑ. Pith
ⓒ. Endodermis
ⓓ. Cortex
Correct Answer: Cortex
Explanation: In a dicot stem with vascular bundles arranged in a circle, the cortex is the tissue that lies directly outside the vascular bundles. The cortex is composed of parenchyma cells that store food and may assist in water and mineral absorption. The epidermis is the outermost protective layer of the stem, while the pith is located at the center of the stem. The endodermis is a tissue found in roots, not stems. Therefore, the cortex is the layer that lies just outside the vascular bundles in dicot stems.
188. The vascular bundle ring in dicot stems allows for which of the following adaptations in plant growth?
ⓐ. Ability to form secondary xylem and phloem for increased plant girth and mechanical strength
ⓑ. Ability to form aerenchyma in response to waterlogging
ⓒ. Ability to store starch in the central pith of the stem
ⓓ. Ability to form chloroplasts for photosynthesis in the stem
Correct Answer: Ability to form secondary xylem and phloem for increased plant girth and mechanical strength
Explanation: The vascular bundle ring in dicot stems enables the plant to undergo secondary growth through the activity of the cambium. This cambium produces new xylem (wood) toward the center and new phloem toward the outer edge, which increases the stem’s girth over time. Secondary growth is crucial for the development of woody plants, providing structural support and allowing the plant to grow in height and strength. Aerenchyma formation, starch storage, and chloroplast formation are not associated with the vascular bundle ring’s role in secondary growth. Hence, the primary adaptation facilitated by the vascular bundle ring is the formation of secondary xylem and phloem.
189. Which of the following best describes the vascular bundles in a dicot stem during secondary growth?
ⓐ. The bundles are scattered throughout the stem with no central pith
ⓑ. The bundles form a ring of xylem only, with no phloem involvement
ⓒ. The bundles are arranged in a single central core of xylem surrounded by phloem
ⓓ. The bundles are arranged in a circle, surrounded by cambium that enables secondary growth
Correct Answer: The bundles are arranged in a circle, surrounded by cambium that enables secondary growth
Explanation: In dicot stems, the vascular bundles are typically arranged in a circle during primary growth. As the plant undergoes secondary growth, the cambium between the xylem and phloem in each vascular bundle becomes active and produces additional xylem (wood) and phloem. This process leads to an increase in the stem’s girth, contributing to the overall mechanical strength and growth of the plant. The central pith remains inside the vascular ring, and the bundles are not scattered or concentrated in a single core. Therefore, the correct description is that the vascular bundles are arranged in a circle with cambium facilitating secondary growth.
190. A student observes a dicot stem with vascular bundles arranged in a ring. Which of the following best describes the function of the cambium in these bundles?
ⓐ. The cambium produces new phloem to transport sugars from leaves to roots
ⓑ. The cambium produces new xylem to conduct water from roots to leaves
ⓒ. The cambium produces both xylem and phloem to enable secondary growth and increase stem girth
ⓓ. The cambium acts as a barrier to protect the stem from pathogens
Correct Answer: The cambium produces both xylem and phloem to enable secondary growth and increase stem girth
Explanation: The cambium in dicot stems is a meristematic tissue that plays a crucial role in secondary growth. It forms new xylem toward the center and new phloem toward the outside. This process of producing additional xylem and phloem contributes to the increase in girth of the stem, which is characteristic of dicot plants. The cambium is not involved in directly transporting sugars or water, and it does not serve as a protective barrier. Instead, its primary function is to facilitate secondary growth by adding layers of vascular tissue, leading to the thickening of the stem.
191. In a dicot stem, the vascular bundles are arranged:
ⓐ. In scattered bundles throughout the ground tissue
ⓑ. In a complete ring around the central pith
ⓒ. In a single large bundle in the center
ⓓ. Randomly distributed with no clear pattern
Correct Answer: In a complete ring around the central pith
Explanation: In dicot stems, vascular bundles are typically arranged in a circle around the central pith. This arrangement allows for secondary growth, which results in the thickening of the stem over time. The xylem faces inward, and the phloem faces outward, with a cambium layer in between that facilitates the formation of new vascular tissue. This is a characteristic feature of dicot stems and contrasts with monocot stems, where vascular bundles are scattered throughout the stem.
192. Which of the following features is most characteristic of dicot stems with vascular bundles arranged in a ring?
ⓐ. Vascular bundles are scattered throughout the stem with no central pith
ⓑ. The presence of secondary growth due to the cambium in the bundles
ⓒ. Vascular bundles are arranged in a circle around a central pith with no cambium
ⓓ. The stem is herbaceous and cannot grow in thickness
Correct Answer: The presence of secondary growth due to the cambium in the bundles
Explanation: In dicot stems, the vascular bundles arranged in a ring around the central pith have a cambium layer between the xylem and phloem. The cambium is responsible for secondary growth, which increases the stem’s girth by producing more xylem and phloem. This secondary growth is a defining characteristic of dicot stems and allows them to grow in thickness over time. The presence of cambium makes these stems capable of becoming woody, unlike monocot stems, which typically do not have secondary growth.
193. A dicot stem with vascular bundles arranged in a ring will most likely show:
ⓐ. Scattered vascular bundles with no central pith
ⓑ. A single central vascular bundle with surrounding ground tissue
ⓒ. Secondary growth, producing both xylem and phloem
ⓓ. An absence of cambium and limited growth
Correct Answer: Secondary growth, producing both xylem and phloem
Explanation: The arrangement of vascular bundles in a ring in dicot stems is associated with secondary growth, where the cambium between the xylem and phloem produces additional layers of vascular tissue. This leads to an increase in stem diameter, which is a key feature of dicots. The presence of cambium enables the stem to continue growing in thickness as new layers of xylem and phloem are added. This is different from monocots, which generally do not undergo secondary growth in their stems.
194. In a dicot stem with vascular bundles arranged in a ring, the cambium is responsible for:
ⓐ. The formation of aerenchyma in the stem for gas exchange
ⓑ. The growth of the epidermis and cuticle for protection
ⓒ. The production of secondary xylem and phloem, leading to thickening of the stem
ⓓ. The formation of the root cap for protection of the root tip
Correct Answer: The production of secondary xylem and phloem, leading to thickening of the stem
Explanation: In dicot stems, the cambium is the meristematic tissue found between the xylem and phloem in each vascular bundle. It is responsible for secondary growth, which involves the production of secondary xylem (wood) and secondary phloem. This growth adds layers of vascular tissue, contributing to the thickening of the stem over time. The cambium does not form aerenchyma or protect the root tip; its main role is to enable secondary growth in stems.
195. The radial arrangement of vascular bundles in dicot stems is important for:
ⓐ. Allowing secondary growth to increase the stem’s girth
ⓑ. Facilitating the movement of water from leaves to roots
ⓒ. Preventing water loss through the epidermis
ⓓ. Enhancing the root cap’s ability to protect the root tip
Correct Answer: Allowing secondary growth to increase the stem’s girth
Explanation: The radial arrangement of vascular bundles in dicot stems, where xylem and phloem alternate in a ring, is key for enabling secondary growth. The cambium layer between these tissues produces new xylem and phloem, allowing the stem to increase in girth over time. This growth pattern is characteristic of dicot stems, allowing them to become woody and structurally stronger as they mature. The other options are unrelated to the primary function of the vascular bundle arrangement in dicot stems.
196. The presence of vascular bundles in a ring in a dicot stem is most closely associated with:
ⓐ. The ability to form a thick outer cuticle to prevent water loss
ⓑ. A reduced number of xylem poles and a small central pith
ⓒ. The presence of adventitious roots along the stem
ⓓ. Secondary growth that increases the stem’s diameter
Correct Answer: Secondary growth that increases the stem’s diameter
Explanation: The key characteristic of dicot stems with vascular bundles arranged in a ring is secondary growth. This type of growth occurs because the cambium layer between the xylem and phloem in each vascular bundle divides to produce more xylem and phloem, contributing to an increase in stem girth. This allows dicot plants to grow larger in diameter and develop into woody structures. The other options refer to different features that are not directly related to the vascular bundle arrangement in dicot stems.
197. A dicot stem with vascular bundles in a ring will typically have which of the following tissues in the center of the stem?
ⓐ. A large central pith composed of parenchyma cells
ⓑ. A central vascular bundle surrounded by phloem
ⓒ. Aerenchyma for gas exchange between tissues
ⓓ. Secondary xylem and phloem forming a woody core
Correct Answer: A large central pith composed of parenchyma cells
Explanation: In dicot stems, the center of the stem is typically filled with a large central pith made of parenchyma cells. The pith serves as storage and provides internal support to the plant. The vascular bundles, which are arranged in a ring around the pith, consist of xylem and phloem and are responsible for the transport of water, nutrients, and sugars. Aerenchyma and secondary growth features like wood formation are not found in the central region of the stem, especially in young dicot stems.
198. In a dicot stem with vascular bundles arranged in a ring, which of the following processes is directly facilitated by the cambium?
ⓐ. Formation of secondary phloem and xylem, contributing to stem thickening
ⓑ. Translocation of sugars through the phloem in the stem
ⓒ. Absorption of water and nutrients from the soil by the root
ⓓ. Regulation of gas exchange through stomata in the epidermis
Correct Answer: Formation of secondary phloem and xylem, contributing to stem thickening
Explanation: The cambium is a meristematic tissue found between the xylem and phloem in dicot stems. Its main role is to produce secondary xylem (wood) and secondary phloem, leading to the thickening of the stem during secondary growth. This is a key process in woody plants, allowing them to grow in diameter as they mature. The other processes listed—sugar transport, water and nutrient absorption, and gas exchange—are not directly facilitated by the cambium but involve different tissues like phloem, roots, and stomata.
199. Which of the following is a consequence of having vascular bundles arranged in a ring in a dicot stem?
ⓐ. The stem is more flexible and less prone to bending
ⓑ. The stem can undergo secondary growth, leading to an increase in diameter
ⓒ. The stem has a central pith that is used for photosynthesis
ⓓ. The stem lacks xylem and phloem in its structure
Correct Answer: The stem can undergo secondary growth, leading to an increase in diameter
Explanation: The arrangement of vascular bundles in a ring around the central pith is a key feature of dicot stems. This arrangement allows for secondary growth, which is the process by which the cambium layer between the xylem and phloem produces additional layers of these tissues, causing the stem to increase in diameter. This is essential for the growth of woody plants. The flexibility of the stem, presence of a central pith, and absence of xylem and phloem are not consequences of the vascular bundle arrangement in dicot stems. Therefore, the correct answer is secondary growth leading to increased stem diameter.
200. Which feature is most likely to be seen in the vascular bundles of a dicot stem with a ring arrangement?
ⓐ. Xylem and phloem are arranged in separate bundles with no interconnection
ⓑ. The bundles are scattered with no distinct organization
ⓒ. The phloem is located at the center, surrounded by xylem
ⓓ. Cambium is present between xylem and phloem, allowing for secondary growth
Correct Answer: Cambium is present between xylem and phloem, allowing for secondary growth
Explanation: In dicot stems, vascular bundles are arranged in a ring, and the cambium layer between the xylem and phloem is responsible for secondary growth. The cambium produces new layers of xylem and phloem, which contributes to an increase in the stem’s diameter. This is a characteristic feature of dicots, allowing them to undergo secondary growth. The other options do not accurately describe the typical vascular bundle arrangement in dicot stems, as phloem is usually located on the outside of xylem, and the presence of cambium is crucial for secondary growth.