If you are comparing secondary growth initiation, the vascular cambium ring in a primary dicotyledonous root differs fundamentally from that of a dicotyledonous stem because the root cambium is:
Explanation: In a dicotyledonous stem, vascular cambium is partially primary in origin (intrafascicular cambium). In contrast, in a dicot root, the cambium ring is completely secondary in origin. It originates from the conjunctive tissue located just below the phloem bundles and a portion of pericycle tissue lying above the protoxylem.
Question 52 of 115
📘 CLASS XI
Why is collenchyma completely absent in the primary cortex of roots but highly abundant as a hypodermis in young dicotyledonous stems?
Explanation: Collenchyma is a living mechanical tissue that provides tensile strength and elasticity. Aerial organs, such as young dicot stems, require mechanical support to withstand wind-induced bending and shearing stress. Since roots are underground and fully supported by the surrounding soil, they do not require collenchyma.
Question 53 of 115
📘 CLASS XI
If a microscopic needle is pushed radially inward from the cortex of a sunflower root, what is the first cell layer of the stele it will penetrate?
Explanation: The stele is defined as all tissues on the inner side of the endodermis, which includes the pericycle, vascular bundles, and pith. Since the endodermis is the innermost boundary of the cortex, the very first layer of the stele encountered immediately after passing the endodermis is the pericycle.
Question 54 of 115
📘 CLASS XI
If grass leaves are treated with a metabolic inhibitor that keeps their adaxial bulliform cells permanently turgid even under severe environmental drought, what will be the physiological outcome?
Explanation: Bulliform cells are large, empty, colourless adaxial epidermal cells. When they are turgid (having absorbed water), the leaf surface is exposed. When they lose water due to water stress and become flaccid, they cause the leaves to curl inward to minimize water loss. If they are artificially kept turgid, the leaves will remain exposed, leading to excessive transpiration and damage.
Question 55 of 115
📘 CLASS XI
Under a microscope, you observe a vascular bundle containing a distinct, water-filled cavity on its inner side next to the protoxylem. This feature is a diagnostic marker of which organ?
Explanation: The presence of water-containing cavities within the vascular bundles is a unique anatomical diagnostic feature of monocotyledonous stems. These cavities form due to the disintegration of early-formed protoxylem elements during development.
Question 56 of 115
📘 CLASS XI
A vascular bundle in an unlabeled slide has its metaxylem located toward the center of the organ and its protoxylem located toward the periphery. What is this xylem arrangement, and where is it found?
Explanation: When the earliest-formed primary xylem (protoxylem) lies towards the periphery and the later-formed primary xylem (metaxylem) lies towards the center, the arrangement is called exarch. This exarch xylem arrangement is a classic diagnostic feature of roots. Stems, on the other hand, show an endarch arrangement.
Question 57 of 115
📘 CLASS XI
In a primary dicotyledonous stem, the endodermis is functionally referred to as the "starch sheath." What is the physiological reason for this designation?
Explanation: In a young dicot stem, the cells of the innermost cortical layer (the endodermis) are exceptionally rich in starch grains. Because of this structural and storage characteristic, this layer is referred to as the starch sheath.
Question 58 of 115
📘 CLASS XI
In a dorsiventral leaf, what is the anatomical nature of the specialized cell layer that surrounds the vascular bundles in the veins?
Explanation: In dorsiventral leaves, the vascular bundles in the veins and midrib are not exposed directly to the mesophyll; instead, they are surrounded by a layer of thick-walled bundle sheath cells which provide mechanical protection and help regulate transport.
Question 59 of 115
📘 CLASS XI
A student notices that a tomato plant stem releases a sticky, protective fluid when gently brushed. Which epidermal appendage is responsible for this secretion?
Explanation: On the stem, the epidermal hairs are called trichomes. These trichomes are usually multicellular, can be branched or unbranched, and soft or stiff. NCERT specifically notes that they may even be secretory, producing defensive or aromatic fluids.
Question 60 of 115
📘 CLASS XI
If you perform a chemical and histological analysis of a primary stem and find sieve tubes and companion cells, but note a complete absence of phloem parenchyma, you are examining:
Explanation: In monocotyledons (such as maize), a key anatomical feature of the vascular bundle is that the phloem parenchyma is absent. Dicotyledonous stems (like sunflower and hibiscus) possess phloem parenchyma as a normal constituent of their complex tissues.
