In a monocot stem, what tissue makes up the vast majority of the internal volume, and what is its cellular nature?
Explanation: The monocot stem has a large, conspicuous parenchymatous ground tissue which surrounds the scattered vascular bundles. Parenchyma cells are thin-walled and usually loosely arranged.
Question 42 of 115
📘 CLASS XI
If you are comparing a primary dicot root with a young dicot stem, which of the following is a key common feature shared by their innermost cortical layers?
Explanation: In both the primary dicot root and the dicot stem, the innermost layer of the cortex is called the endodermis. (Note: In roots, it contains suberin Casparian strips, whereas in dicot stems, it is rich in starch grains and functions as a starch sheath).
Question 43 of 115
📘 CLASS XI
Which of the following statements correctly distinguishes the vascular bundle arrangement of a monocotyledonous stem from a dicotyledonous stem?
Explanation: In monocot stems, vascular bundles are conjoint, closed, and scattered. In dicot stems, they are arranged in a ring, conjoint, and open.
Question 44 of 115
📘 CLASS XI
What happens to the centrally located cells of a young dicotyledonous stem as it develops?
Explanation: In a dicot stem, a large number of rounded, parenchymatous cells with large intercellular spaces occupy the central portion of the stem, constituting the pith.
Question 45 of 115
📘 CLASS XI
Why is the epidermis of a young dicotyledonous stem covered with a waxy cuticle, and does it possess stomata?
Explanation: The epidermis is the outermost protective layer of the dicot stem. It is covered with a thin layer of cuticle to prevent water loss and may bear trichomes and a few stomata to allow regulated gas exchange.
Question 46 of 115
📘 CLASS XI
A leaf oriented horizontally in a temperate environment is exposed to direct sunlight on its upper surface. How does the stomatal distribution on this leaf adapt to minimize excessive transpiration?
Explanation: In a dorsiventral (dicotyledonous) leaf, the abaxial (lower) epidermis generally bears more stomata than the adaxial (upper) epidermis. The adaxial epidermis may even lack stomata. This adaptation protects the stomata from direct sunlight, reducing excessive water loss.
Question 47 of 115
📘 CLASS XI
If you examine a leaf cross-section and observe tightly packed, vertically elongated, columnar parenchymatous cells on the upper side, and loosely arranged rounded cells with large air spaces on the lower side, what can you conclude?
Explanation: In a dorsiventral leaf, the mesophyll is differentiated into two types of parenchymatous cells: the adaxially placed palisade parenchyma (vertically elongated, parallel columnar cells) and the abaxially placed spongy parenchyma (oval or round, loosely arranged cells with large air spaces and cavities).
Question 48 of 115
📘 CLASS XI
How does the internal tissue organization of an isobilateral (monocotyledonous) leaf compare with that of a dorsiventral (dicotyledonous) leaf?
Explanation: In an isobilateral leaf, the stomata are present on both the surfaces of the epidermis. Furthermore, unlike the dorsiventral leaf, the mesophyll is not differentiated into palisade and spongy parenchyma; it is uniform throughout.
Question 49 of 115
📘 CLASS XI
On a hot, dry afternoon, lawn grass leaves can be observed curling inward. What specific cells are responsible for this physiological defense mechanism against water stress, and what is their state?
Explanation: In grasses, certain adaxial epidermal cells modify into large, empty, colourless cells called bulliform cells. When they are turgid (having absorbed water), the leaf surface is exposed. When they are flaccid due to water stress, they make the leaves curl inwards to minimize water loss.
Question 50 of 115
📘 CLASS XI
Why does a vertical section of a grass leaf show vascular bundles that are nearly uniform in size (except in the midrib), whereas a vertical section of a hibiscus (dicot) leaf shows vascular bundles of widely varying sizes?
Explanation: In a dicot leaf, the veins vary in thickness because of reticulate venation, which directly causes the sizes of the vascular bundles to vary depending on the vein size. In monocot leaves, the parallel venation is reflected in the near-similar sizes of vascular bundles (except in main veins) along the leaf lamina.
