In a primary dicotyledonous root, what makes the pericycle uniquely vital for both vegetative propagation and structural growth?
Explanation: Next to the endodermis in primary roots lies the pericycle, composed of thick-walled parenchymatous cells. The pericycle is highly active developmentally because the initiation of lateral roots and the vascular cambium during secondary growth takes place in these cells.
Question 82 of 115
📘 CLASS XI
If you are comparing a primary dicotyledonous root and a monocotyledonous root, which of the following quantitative and structural characteristics would you use to tell them apart under a microscope?
Explanation: In a dicot root, there are fewer xylem and phloem patches (usually two to four), and the pith is small or inconspicuous. In contrast, the monocot root has more than six (polyarch) xylem bundles, and its pith is large and well-developed.
Question 83 of 115
📘 CLASS XI
Sclerenchyma is a dead permanent tissue that provides mechanical rigidity. In a primary dicotyledonous stem, where is this tissue specifically localized to protect the vascular bundles?
Explanation: In a dicot stem, the pericycle is present on the inner side of the endodermis and above the phloem in the form of semi-lunar patches of sclerenchyma. This placement acts as a mechanical shield over the delicate conducting cells of the phloem.
Question 84 of 115
📘 CLASS XI
Why does the absence of phloem parenchyma in monocotyledonous stems act as a diagnostic evolutionary feature of this group?
Explanation: In the monocotyledonous stem, the phloem parenchyma is completely absent. This is a key taxonomic and diagnostic anatomical difference used to distinguish monocots from dicots, as dicotyledonous stems normally possess phloem parenchyma.
Question 85 of 115
📘 CLASS XI
In a leaf cross-section, you observe that the veins vary greatly in thickness. What type of leaf is this, and how does this variation affect the size of its vascular bundles?
Explanation: In a dorsiventral (dicot) leaf, the veins show reticulate venation and vary significantly in thickness. Because the size of the vascular bundles is dependent on the size of the veins, the bundles are of varying sizes.
Question 86 of 115
📘 CLASS XI
Why are the stomata in isobilateral leaves distributed on both the upper and lower surfaces, whereas they are primarily restricted to the lower surface in dorsiventral leaves?
Explanation: Dorsiventral (dicot) leaves are oriented horizontally; the upper (adaxial) surface faces direct sunlight, so keeping fewer or no stomata there minimizes transpirational water loss. Isobilateral (monocot) leaves are held nearly vertically, receiving equal light on both sides, which is why stomata are present on both surfaces of the epidermis.
Question 87 of 115
📘 CLASS XI
What would happen to a grass plant during a hot, dry period if its adaxial bulliform cells were structurally reinforced with lignin, making them permanently rigid?
Explanation: In grasses, certain adaxial epidermal cells modify into large, empty, colourless bulliform cells. When turgid, they expose the leaf blade; when they become flaccid due to water stress, they cause the leaves to curl inward to minimize water loss. If these cells were lignified and rigid, they could not change turgor or collapse, preventing the leaf from rolling inward to survive drought.
Question 88 of 115
📘 CLASS XI
In a dorsiventral leaf, what is the spatial and structural organization of the mesophyll tissue that optimizes both light capture and gas exchange?
Explanation: In a dorsiventral leaf, the mesophyll is divided into two distinct zones: the adaxially placed palisade parenchyma (elongated cells arranged vertically and parallel to each other to maximize light capture) and the abaxially placed spongy parenchyma (oval or round, loosely arranged cells with numerous large spaces and air cavities to facilitate rapid gas exchange).
Question 89 of 115
📘 CLASS XI
In a primary plant body, how does the fundamental "ground tissue system" compare in stems/roots versus leaves?
Explanation: Ground tissue comprises all tissues except the epidermis and vascular bundles. In primary stems and roots, it is divided into distinct zones like cortex, pericycle, pith, and medullary rays. In leaves, it is undifferentiated into these zones and is composed of thin-walled, chloroplast-containing parenchymatous cells called mesophyll.
Question 90 of 115
📘 CLASS XI
What is the developmental origin of the vascular cambium that forms in a primary dicotyledonous root?
Explanation: In a dicot root, the vascular cambium is completely secondary in origin. It is initiated from the parenchymatous cells of the conjunctive tissue lying below the phloem patches and a portion of the pericycle tissue lying above the protoxylem.
