Which of the following combinations of structures collectively constitutes the 'stomatal apparatus'?
Explanation: NCERT defines the stomatal apparatus as the collective unit made up of the stomatal aperture (pore), the enclosing guard cells, and the surrounding specialized subsidiary cells.
Question 62 of 115
📘 CLASS XI
What physiological organelle is present in guard cells but completely absent in typical general epidermal cells?
Explanation: While general epidermal cells lack chloroplasts, the guard cells possess chloroplasts. This presence is functionally vital because chloroplasts enable the guard cells to generate the solutes and energy needed to regulate turgor-driven stomatal opening and closing.
Question 63 of 115
📘 CLASS XI
In a primary dicot stem, the medullary rays lie in between the vascular bundles. What is their cellular nature and primary function?
Explanation: Medullary rays are composed of a few layers of radially placed parenchymatous cells situated in between the vascular bundles of dicot stems. Being parenchymatous and radially oriented, they are designed to facilitate lateral (radial) conduction of water and organic nutrients.
Question 64 of 115
📘 CLASS XI
You count 8 distinct patches of primary xylem alternating with 8 patches of primary phloem in a primary root cross-section. What plant group does this specimen belong to?
Explanation: Dicot roots have fewer xylem bundles, usually two to four. In contrast, monocotyledonous roots typically contain more than six xylem bundles, a condition referred to as polyarch. A root with 8 xylem patches is polyarch, confirming it is a monocot.
Question 65 of 115
📘 CLASS XI
Why is the outermost epidermal layer of a primary root specifically called 'epiblema' rather than 'epidermis'?
Explanation: The outermost layer of the root is called the epiblema. It is structurally modified for absorption: it lacks a cuticle (which would block water), possesses no stomata, and has specialized cells that protrude as unicellular root hairs to maximize water and mineral absorption from the soil.
Question 66 of 115
📘 CLASS XI
If you observe the parenchymatous cells lying between the xylem and phloem patches in a primary dicotyledonous root, you are looking at:
Explanation: In a primary dicot root, the parenchymatous cells which lie between the xylem and the phloem are called conjunctive tissue. Later in development, the vascular cambium initiates in part from this conjunctive tissue.
Question 67 of 115
📘 CLASS XI
How is the pericycle structurally organized in a primary dicotyledonous stem?
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 provides localized mechanical protection directly over the vascular bundles.
Question 68 of 115
📘 CLASS XI
Why is the upper (adaxial) surface of a dorsiventral leaf typically a darker green than its lower (abaxial) surface?
Explanation: In a dorsiventral leaf, the mesophyll is differentiated. The adaxially placed palisade parenchyma consists of vertically elongated cells arranged parallel and compactly. Because these cells are packed tightly and contain the highest concentration of chloroplasts to capture direct sunlight, the upper surface appears darker green.
Question 69 of 115
📘 CLASS XI
In a primary root, the cortex consists of several layers of thin-walled parenchymatous cells. What is the physiological significance of their conspicuous intercellular spaces?
Explanation: The root cortex is made of thin-walled parenchymatous cells with conspicuous intercellular spaces. This open arrangement allows absorbed water and minerals to move easily and rapidly via the apoplastic pathway through the cortex before encountering the barrier of the endodermis.
Question 70 of 115
📘 CLASS XI
If you compare vertical sections of a grass leaf and a hibiscus leaf under a microscope, what difference in vascular bundle sizes will you observe, and why?
Explanation: In monocots (like grasses), parallel venation is reflected in the near-similar sizes of vascular bundles (except in main veins). In dicots (like hibiscus), reticulate venation means the veins vary greatly in thickness across the lamina, causing the size of the vascular bundles to vary accordingly.
