201. In a young dicot stem, the living corner-thickened cells of the hypodermis prematurely become dead and uniformly lignified, while the epidermis and vascular bundles remain intact. During continued elongation, the most likely change is:
ⓐ. increased food conduction because the hypodermis becomes phloem
ⓑ. unrestricted elongation because lignified walls stretch more readily
ⓒ. greater rigidity but reduced flexibility of the growing stem
ⓓ. immediate loss of water conduction from every vascular bundle
Correct Answer: greater rigidity but reduced flexibility of the growing stem
Explanation: A normal collenchymatous hypodermis contains living cells with unevenly thickened primary walls. This construction supports a young stem while still permitting local stretching and bending as the organ elongates. Uniform lignification would make the cells more sclerenchyma-like: their walls would become mechanically rigid, and death at maturity would remove the living flexibility characteristic of collenchyma. The stem might resist small deformation more strongly at first, but it would accommodate continued growth less effectively and would be more liable to stiffness or cracking when elongation and bending occur. The change does not convert the hypodermis into phloem or xylem, because tissue identity is not reassigned merely by adding lignin. Existing vascular bundles can initially continue conduction. The predicted outcome follows from replacing flexible primary-wall support with rigid lignified support in an organ that is still growing.
202. Consider the following statements about the collenchymatous hypodermis of a typical young dicot stem.
I. It occurs immediately below the epidermis.
II. It is composed of living cells.
III. It contributes mechanical support without imposing complete rigidity.
IV. It consists mainly of dead cells with uniformly lignified walls.
ⓐ. Only statements I and IV are correct
ⓑ. Only statements II and III are correct
ⓒ. Only statements I, II and IV are correct
ⓓ. Only statements I, II and III are correct
Correct Answer: Only statements I, II and III are correct
Explanation: The hypodermis of a young dicot stem commonly consists of several collenchymatous layers immediately beneath the epidermis. Its cells remain living and possess unevenly thickened primary walls. These features provide strength while preserving flexibility, an important combination in an organ that is still elongating or bending. Uniformly lignified dead cells would indicate sclerenchyma rather than collenchyma. The fourth statement therefore assigns the structure of a more rigid supporting tissue to the hypodermis described here. The valid statements combine position, viability and mechanical behaviour. Statements I, II and III jointly identify the tissue by location, viability and mechanical behaviour. Statement IV instead describes sclerenchyma and would predict rigid support with little capacity for flexible growth.
203. A tracer enters the cortical region of a young dicot stem and spreads readily through a broad zone of rounded thin-walled cells with conspicuous intercellular spaces. It does not enter the subepidermal corner-thickened band. The broad zone is:
ⓐ. cortical parenchyma
ⓑ. sclerenchymatous pericycle
ⓒ. vascular cambium
ⓓ. epidermis
Correct Answer: cortical parenchyma
Explanation: The broad region lies within the cortex but beneath the collenchymatous hypodermis. Its cells are rounded, thin-walled and separated by conspicuous intercellular spaces, which identifies ordinary cortical parenchyma. Such living cells can participate in storage and local metabolic activity. The subepidermal band excluded by the tracer is structurally different because collenchyma is more compact and has uneven wall thickenings. The pericycle occurs farther inward as sclerenchymatous patches, and vascular cambium lies within open vascular bundles. The epidermis forms the outer covering rather than a broad internal zone. Position and cell arrangement together support the identification. The tracer pattern also distinguishes the broad cortical parenchyma from the compact hypodermis: conspicuous intercellular spaces permit easier lateral spread, while the corner-thickened band is more tightly packed.
204. The following regions are compared in a young dicot stem.
| Region | Wall pattern | Intercellular spaces | Principal role |
|---|
| P | Unevenly thickened | Very limited | Flexible support |
| Q | Thin and nearly uniform | Conspicuous | Storage and local metabolism |
| R | Thick and lignified | Very limited | Rigid support outside phloem |
Which interpretation is accurate?
ⓐ. P-cortical parenchyma, Q-sclerenchymatous pericycle, R-collenchymatous hypodermis
ⓑ. P-collenchymatous hypodermis, Q-cortical parenchyma, R-sclerenchymatous pericycle
ⓒ. P-sclerenchymatous pericycle, Q-collenchymatous hypodermis, R-cortical parenchyma
ⓓ. P-epidermis, Q-starch sheath, R-medullary-ray parenchyma
Correct Answer: P-collenchymatous hypodermis, Q-cortical parenchyma, R-sclerenchymatous pericycle
Explanation: Region P shows the characteristic living, unevenly thickened and closely packed organisation of collenchymatous hypodermis. Region Q contains thin-walled cells with conspicuous spaces, matching ordinary cortical parenchyma. Region R is heavily reinforced and lies outside the phloem, identifying the sclerenchymatous pericycle of the young dicot stem. The three neighbouring regions all contribute to the outer stem body while differing substantially in wall construction and function. Flexible support is concentrated in P, storage and metabolism in Q and rigid reinforcement in R. Classification therefore requires synthesis of wall pattern, packing and position rather than use of a single mechanical property. P and Q are both living, but their wall patterns and packing explain their different mechanical and metabolic roles. R is dead and lignified, placing it outside the living cortical tissues and linking it with rigid reinforcement.
205. The innermost cortical layer of a typical young dicot stem is called the starch sheath because its cells:
ⓐ. produce root hairs
ⓑ. form perforated conducting tubes
ⓒ. contain abundant starch grains
ⓓ. possess Casparian strips as their only defining feature
Correct Answer: contain abundant starch grains
Explanation: The endodermal layer of a typical young dicot stem contains conspicuous starch grains and is known as the starch sheath. It forms the innermost boundary of the differentiated cortex. Root hairs arise from the root epiblema, while perforated tubes are formed by xylem vessel elements. Casparian strips are especially important in the root endodermis, but the identifying feature emphasised for the stem layer is its starch content. The name links a visible cellular reserve with the anatomical position of the layer. It should not be interpreted as meaning that every starch-storing cell throughout the plant belongs to the endodermis. In practical identification, both its innermost cortical position and starch reaction should agree before assigning the label.
206. Assertion: The root endodermis and the starch sheath of a young dicot stem can both mark the inner boundary of the cortex.
Reason: Corresponding anatomical positions may show organ-specific specialisations, such as Casparian strips in roots and starch-rich cells in young dicot stems.
ⓐ. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
ⓑ. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
ⓒ. Assertion is true and Reason is false; the false Reason cannot explain the Assertion
ⓓ. Assertion is false and Reason is true; the true Reason cannot explain a false Assertion
Correct Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
Explanation: The Assertion is true. In a primary root, the endodermis is the compact innermost cortical layer separating the broad cortex from the stele. In a young dicot stem, the innermost cortical layer is also termed endodermis and is commonly recognised as the starch sheath because its cells contain conspicuous starch grains. The Reason is also true and explains why the same broad positional relation does not require identical specialisation in the two organs. Root endodermal cells are especially associated with suberised Casparian strips that regulate wall-pathway movement, whereas the stem layer is commonly identified by starch storage. Both layers occupy the cortical boundary, but their conspicuous structural or chemical features reflect organ context. Anatomical comparison must combine position with organ-specific cell properties rather than treating one feature as universal.
207. Stem sections P and Q are treated with a starch-detecting reagent.
| Section | Observation |
|---|
| P | A continuous innermost cortical layer gives a strong starch reaction. |
| Q | The corresponding layer gives no reaction, although outer cortical tissues remain normal. |
The most justified interpretation is:
ⓐ. P lacks a starch sheath, while Q retains a normal starch-rich endodermal layer.
ⓑ. P has a starch-rich pith, while Q lacks a differentiated cortical region.
ⓒ. P has a starch sheath, whereas Q lacks starch in the same endodermal layer.
ⓓ. P contains secondary xylem, while Q contains only primary phloem tissue.
Correct Answer: P has a starch sheath, whereas Q lacks starch in the same endodermal layer.
Explanation: The strongly reacting layer in P lies at the innermost boundary of the cortex, precisely where the dicot-stem endodermis occurs. Its starch content identifies it as the starch sheath. In Q, the corresponding anatomical layer remains present but no longer gives the reaction, indicating loss or depletion of starch rather than complete absence of the cortex. The test does not identify pith or vascular tissues; the reaction is localised specifically to the cortical boundary. Observation and inference must be kept separate: the reagent reveals starch, while anatomical position identifies the reacting cells as endodermal. The comparison shows that the name starch sheath depends on characteristic cellular contents as well as location.
208. Arrange the following structures from the innermost cortex toward the centre of a young dicot stem.
P. Pith
Q. Starch sheath
R. Sclerenchymatous pericycle
S. Ring of vascular bundles
T. Medullary rays between bundles
ⓐ. R → Q → S and T → P
ⓑ. Q → S → R → P → T
ⓒ. Q → R → S and T → P
ⓓ. S → R → Q → T → P
Correct Answer: Q → R → S and T → P
Explanation: Moving inward from the innermost part of the cortex, the starch sheath is encountered first. It represents the endodermal boundary of the young dicot stem and commonly contains starch grains. Immediately internal to it are the sclerenchymatous patches representing the pericycle. The vascular bundles then occur in a ring, while medullary rays extend through the spaces between adjacent bundles. The bundles and rays consequently occupy the same broad radial region rather than forming two successive continuous layers. After this vascular region is crossed, the centrally located pith is reached. The correct sequence is thus starch sheath, sclerenchymatous pericycle, vascular bundles together with intervening medullary rays, and finally the pith.
209. Match each dicot-stem structure with its characteristic position or form. A Column II entry is used once.
| Column I | Column II |
|---|
| P. Starch sheath | 1. Radial parenchymatous band between vascular bundles |
| Q. Pericycle | 2. Central region of rounded parenchymatous cells |
| R. Medullary ray | 3. Innermost cortical layer rich in starch |
| S. Pith | 4. Semilunar sclerenchymatous patches external to phloem |
ⓐ. P-4, Q-3, R-2, S-1
ⓑ. P-3, Q-4, R-1, S-2
ⓒ. P-1, Q-2, R-4, S-3
ⓓ. P-3, Q-1, R-2, S-4
Correct Answer: P-3, Q-4, R-1, S-2
Explanation: The starch sheath is the innermost cortical layer and contains abundant starch grains, so P matches entry 3. The pericycle occurs just inside it as semilunar sclerenchymatous patches external to the phloem, fixing Q-4. Medullary rays are radial bands of parenchymatous cells between adjacent vascular bundles, giving R-1. The pith occupies the centre and consists mainly of rounded parenchymatous cells with intercellular spaces, so S-2. The mapping follows both spatial position and tissue construction. Although the rays and pith are both parenchymatous, their geometry within the section differs and prevents them from being treated as the same named region. The mapping also separates two parenchymatous regions: medullary rays are radial bands between bundles, whereas pith is the continuous central region. Position, not cell type alone, fixes their names.
210. Use the arrangement described below. Numerous vascular bundles form a ring. Between each neighbouring pair, a radial strip of living parenchymatous cells extends from the outer ground region toward the central pith. These strips are:
ⓐ. root-hair files
ⓑ. conjunctive tissues of a radial root system
ⓒ. sclerenchymatous bundle sheaths
ⓓ. parenchymatous medullary rays
Correct Answer: parenchymatous medullary rays
Explanation: The section contains vascular bundles arranged in a ring, indicating the typical organisation of a dicot stem rather than the alternating vascular patches of a root. The radial parenchymatous strips between neighbouring bundles are medullary rays. Their orientation allows continuity between central and peripheral ground regions and gives the stem a spoke-like internal pattern. Conjunctive tissue occurs between xylem and phloem patches in roots, not between complete stem bundles. A bundle sheath surrounds an individual bundle rather than filling the interbundle space. Root-hair files occur at the outer root surface. The combination of ringed bundles, radial position and parenchymatous composition establishes the identity of the strips. Their radial orientation allows continuity across the ring of vascular bundles without turning the rays into conducting bundles themselves. The same cells may assist storage and lateral movement within the ground system.
211. Medullary-ray cells are selectively destroyed in a young dicot stem, while the vascular bundles and pith remain intact. The most direct anatomical consequence is:
ⓐ. weaker radial continuity between pith and cortex
ⓑ. conversion of all open bundles into closed bundles
ⓒ. loss of the epidermal cuticle and surface trichomes
ⓓ. reversal of xylem maturation from endarch to exarch
Correct Answer: weaker radial continuity between pith and cortex
Explanation: Medullary rays consist of radially arranged parenchymatous cells positioned between vascular bundles. Their geometry connects the pith region with more peripheral ground tissues and permits radial association across the stem. Destroying these rays interrupts that continuity even if the vascular bundles and pith themselves remain present. Open or closed status depends on cambium within each bundle and is not determined by the survival of interbundle rays. Epidermal structures lie at the outer surface and are not medullary-ray derivatives. Endarch or exarch identity concerns protoxylem position and also remains unchanged. The direct effect is therefore a loss of radial ground-tissue connection rather than a change in bundle type or surface organisation.
212. Consider the following statements about vascular bundles in a typical young dicot stem.
I. They are arranged in a ring.
II. Each bundle is conjoint.
III. Cambium lies between phloem and xylem.
IV. Protoxylem lies toward the pith.
ⓐ. Only statements I and III are correct
ⓑ. Only statements II and IV are correct
ⓒ. Only statements I, II and IV are correct
ⓓ. Statements I, II, III and IV are correct
Correct Answer: Statements I, II, III and IV are correct
Explanation: Numerous vascular bundles form a ring around the pith in a typical young dicot stem. Within each bundle, phloem and xylem lie along the same radius, so the bundle is conjoint. A cambial strip occurs between the outer phloem and inner xylem, making the bundle open. Protoxylem lies on the inner side near the pith, while metaxylem lies farther outward, producing an endarch maturation pattern. These features operate at different anatomical levels: ringed distribution describes the whole stem, conjoint and open describe bundle organisation, and endarch describes xylem maturation. Their agreement forms a diagnostic stem pattern. The four statements describe distribution, geometry, cambium and maturation orientation, respectively. Together they define the typical ringed, conjoint open and endarch vascular pattern of a young dicot stem.
213. Two stem sections are compared.
| Feature | Section P | Section Q |
|---|
| Bundle distribution | Ringed | Scattered |
| Cambium in bundles | Present | Absent |
| Ground-tissue differentiation | Cortex, rays and pith distinct | Generally undifferentiated |
| Protoxylem position | Near the pith | Inner side of each bundle |
Which inference is best supported?
ⓐ. P is a monocot root and Q is a dicot root.
ⓑ. P is a dicot stem, whereas Q is a monocot stem.
ⓒ. P and Q are both dicot stems at different ages.
ⓓ. P is a leaf and Q is a radial root section.
Correct Answer: P is a dicot stem, whereas Q is a monocot stem.
Explanation: Section P shows the characteristic combination of a dicot stem: vascular bundles occur in a ring, cambium makes them open and the ground tissue is differentiated into named regions including cortex, medullary rays and pith. Protoxylem near the pith confirms an endarch stem pattern. Section Q has numerous scattered closed bundles embedded in generally undifferentiated ground tissue, which supports a monocot-stem identification. Endarch orientation can occur in both stems and therefore does not by itself separate the specimens. Several characters must be integrated rather than relying on bundle distribution alone. Root sections would show radial vascular patches rather than conjoint stem bundles. The bundle distribution and cambium status are decisive independent characters, while ground-tissue differentiation supplies a third line of evidence. Protoxylem remains on the inner side in both stem types, so that shared endarch feature does not erase the dicot-monocot contrast.
214. A young stem section contains a single epidermis, collenchymatous hypodermis, differentiated cortex, starch sheath, sclerenchymatous pericycle, medullary rays and a large central pith. Its vascular bundles form a ring, and each bundle contains cambium between external phloem and internal xylem. The section is:
ⓐ. a typical monocot root
ⓑ. a typical monocot stem
ⓒ. a typical dicot root
ⓓ. a typical dicot stem
Correct Answer: a typical dicot stem
Explanation: The evidence forms a complete diagnostic set. A differentiated cortex with collenchymatous hypodermis and starch sheath is characteristic of a young dicot stem. Semilunar sclerenchymatous pericycle, radial medullary rays and a distinct central pith further support the same identification. The vascular bundles are arranged in a ring and are conjoint and open because phloem and xylem share a radius with cambium between them. A monocot stem would have scattered closed bundles in generally undifferentiated ground tissue. Roots would possess radial vascular organisation rather than a ring of conjoint bundles. The conclusion follows from convergence of outer, cortical, vascular and central features. No single feature is carrying the diagnosis. The cortex, pericycle, medullary rays, pith, bundle ring and cambium all converge on the same primary dicot-stem plan, making the identification robust even if one structure is poorly preserved.
215. Let \(P_h\), \(C\) and \(X\) represent phloem, cambium and xylem within one vascular bundle. Moving from the stem periphery toward the pith, the correct relation for a typical young dicot stem is:
ⓐ. \(\text{periphery}\rightarrow P_h\rightarrow C\rightarrow X\rightarrow\text{pith}\)
ⓑ. \(\text{periphery}\rightarrow X\rightarrow C\rightarrow P_h\rightarrow\text{pith}\)
ⓒ. \(\text{periphery}\rightarrow C\rightarrow P_h\rightarrow X\rightarrow\text{pith}\)
ⓓ. \(\text{periphery}\rightarrow P_h\rightarrow X\rightarrow C\rightarrow\text{pith}\)
Correct Answer: \(\text{periphery}\rightarrow P_h\rightarrow C\rightarrow X\rightarrow\text{pith}\)
Explanation: In a typical conjoint collateral bundle of a young dicot stem, phloem lies on the outer side and xylem lies toward the pith. Vascular cambium forms a strip between these two conducting tissues. Reading the bundle from the stem periphery inward therefore gives \(\text{periphery}\rightarrow P_h\rightarrow C\rightarrow X\rightarrow\text{pith}\). The relation also explains why the bundle is open: the intervening cambium retains meristematic activity. Endarch xylem places protoxylem on the inner side of the xylem region, still nearer the pith. Reversing phloem and xylem would conflict with the common stem arrangement, while placing cambium outside both tissues would remove its defining intervening position. In set terms, the cambial strip is topologically intermediate between the outer phloem and inner xylem. This relation preserves that adjacency as well as the direction from the organ surface to the pith.
216. Cells between phloem and xylem in stem bundles are supplied with a division marker. Marked cells later produce new vascular derivatives on both sides, while neighbouring differentiated conducting cells remain unlabelled. The most justified conclusion is:
ⓐ. the marked cells form a closed bundle lacking secondary potential
ⓑ. the marked cells are medullary-ray cells outside the bundles
ⓒ. the marked cells constitute vascular cambium in open bundles
ⓓ. the marked cells are protoxylem elements becoming phloem
Correct Answer: the marked cells constitute vascular cambium in open bundles
Explanation: The marked cells lie in the diagnostic position between phloem and xylem. Their incorporation of a division marker demonstrates active proliferation, and their production of new vascular derivatives confirms a meristematic role. These features identify vascular cambium. A bundle containing such cambium is open and has the capacity to form secondary vascular tissues. Medullary rays lie between whole bundles rather than between phloem and xylem within one bundle. Protoxylem consists of differentiated xylem elements and does not transform into phloem. The experiment combines positional, cellular and developmental evidence, making the cambial interpretation stronger than identification from location alone. Appearance of labelled derivatives on both sides links cell division to production of new xylem and phloem, while the unlabelled mature conducting cells show that the marker is not merely staining every vascular cell. This is direct evidence of an intervening meristematic strip.
217. A central region of a young dicot stem consists of many rounded, living parenchymatous cells with large intercellular spaces. Vascular bundles and medullary rays surround it. This region is:
ⓐ. cortical parenchyma
ⓑ. pith parenchyma
ⓒ. sclerenchymatous pericycle
ⓓ. collenchymatous hypodermis
Correct Answer: pith parenchyma
Explanation: The described region lies at the centre of the stem and is enclosed by the ring of vascular bundles and intervening medullary rays. Its rounded living parenchymatous cells and large intercellular spaces are characteristic of pith. Cortex lies outside the vascular region and includes hypodermis, cortical parenchyma and starch sheath. The pericycle occurs as supporting patches just internal to the endodermis and external to the phloem. The hypodermis lies directly beneath the epidermis. Central position is therefore the decisive spatial clue, while cell structure confirms that the region is a ground-tissue storage and metabolic zone rather than a supporting or conducting tissue. Its location also separates it from cortical parenchyma, even though both regions may contain living storage cells.
218. A transverse section has the following outer-to-inner pattern: a cutinised epidermis, collenchymatous hypodermis, cortical parenchyma, starch sheath, sclerenchymatous pericycle, ringed open vascular bundles separated by medullary rays and a central pith. Which change would most specifically make the section inconsistent with a typical young dicot stem?
ⓐ. replacing ringed open bundles with scattered closed bundles in undifferentiated ground tissue
ⓑ. increasing cortical parenchyma while preserving ringed open bundles and a distinct pith
ⓒ. enlarging pith intercellular spaces while preserving cortex, rays and open bundles
ⓓ. increasing starch in the innermost cortex while preserving ringed open vascular bundles
Correct Answer: replacing ringed open bundles with scattered closed bundles in undifferentiated ground tissue
Explanation: The original sequence integrates all major diagnostic regions of a young dicot stem. Ringed conjoint open bundles, differentiated ground tissue, medullary rays and a distinct pith are especially important in that diagnosis. Replacing them with scattered closed bundles embedded in undifferentiated ground tissue introduces the characteristic vascular and ground-tissue organisation of a typical monocot stem. Moderate variation in cortical thickness, pith spacing or starch abundance does not overturn the fundamental dicot-stem plan when the main spatial relations remain intact. The correct change alters several linked diagnostic features rather than one variable quantitative detail. It produces a genuinely different anatomical organisation instead of ordinary variation within the same stem type. The replacement removes the cambium-bearing ring that supports ordinary secondary vascular growth and substitutes the closed-bundle pattern.
219. Consider the following statements about a typical monocot stem.
I. Its hypodermis is commonly sclerenchymatous.
II. Its ground tissue is generally not differentiated into distinct cortex and pith.
III. Its vascular bundles form a single ring around a central pith.
IV. Numerous vascular bundles occur throughout the ground tissue.
ⓐ. Only statements I and III are correct
ⓑ. Only statements I, II and IV are correct
ⓒ. Only statements II and III are correct
ⓓ. Statements I, II, III and IV are correct
Correct Answer: Only statements I, II and IV are correct
Explanation: A typical monocot stem has a sclerenchymatous hypodermis beneath the epidermis, providing firm mechanical support. Inside this layer lies a broad parenchymatous ground tissue that is generally not divided into clearly recognisable cortex, medullary rays and pith. Numerous vascular bundles are scattered through this ground tissue instead of forming the regular ring characteristic of a young dicot stem. Statement III introduces the vascular arrangement of a dicot stem into a monocot-stem description. The valid combination joins three mutually supporting characters: sclerenchymatous hypodermis, undifferentiated ground tissue and scattered bundles. These features are more diagnostic when interpreted together than when any one of them is used alone. Statement III is the only one that conflicts with the typical pattern, since a regular ring and distinct central pith characterise a dicot stem. The other three statements converge on the monocot arrangement.
220. Use the arrangement described below. A stem section has an outer epidermis, several layers of thick-walled dead cells beneath it and a broad internal parenchymatous region without distinct cortex, medullary rays or pith. Numerous vascular bundles occur within this region. The section is most consistent with:
ⓐ. a dicot root with radial vascular tissues
ⓑ. a monocot root with polyarch xylem and a large central pith
ⓒ. a young dicot stem with a zoned cortex
ⓓ. a monocot stem with undifferentiated ground tissue
Correct Answer: a monocot stem with undifferentiated ground tissue
Explanation: The thick-walled dead cells immediately below the epidermis form a sclerenchymatous hypodermis. This differs from the living collenchymatous hypodermis of a typical young dicot stem. The broad internal region lacks separation into cortex, medullary rays and pith, identifying it as the generally undifferentiated ground tissue of a monocot stem. Numerous vascular bundles embedded throughout that region provide additional support for the same conclusion. Roots would show an endodermis, pericycle and radial alternation of xylem and phloem rather than many complete vascular bundles in ground tissue. A dicot stem would usually display a differentiated cortex and ringed bundles. The combined surface, ground-tissue and vascular evidence identifies a typical monocot stem. The combination of a sclerenchymatous hypodermis, undifferentiated ground tissue and numerous bundles is more diagnostic than any one character. It also distinguishes the section from a root, where xylem and phloem would occur as separate radial patches.
