Why is the endodermis of a primary root structurally referred to as "tightly packed" or "barrier-like"?
Explanation: The root endodermis is the innermost layer of the cortex and comprises a single layer of barrel-shaped cells without any intercellular spaces. This compact, gap-free arrangement is essential for its function as a selective barrier.
Question 22 of 115
📘 CLASS XI
What constitutes the 'stele' of a primary root?
Explanation: NCERT defines the stele as all tissues on the inner side of the endodermis such as pericycle, vascular bundles and pith.
Question 23 of 115
📘 CLASS XI
What is the conjunctive tissue in a primary dicotyledonous root?
Explanation: In a dicot root, the parenchymatous cells which lie between the xylem and the phloem are called conjunctive tissue.
Question 24 of 115
📘 CLASS XI
In terms of future developmental potential, what is a key anatomical difference between monocotyledonous and dicotyledonous roots?
Explanation: In dicot roots, vascular cambium initiates in the pericycle cells during secondary growth. However, monocotyledonous roots do not undergo any secondary growth.
Question 25 of 115
📘 CLASS XI
Which of the following correctly traces the path of water moving radially inward from the soil to the root xylem?
Explanation: Water is absorbed by root hairs (protrusions of epiblema), travels through the parenchymatous cortex, crosses the innermost cortical layer (endodermis), moves through the pericycle, and finally enters the xylem.
Question 26 of 115
📘 CLASS XI
A young herbaceous dicot stem needs to withstand the mechanical stress of bending in high winds while continuing to grow in diameter and perform photosynthesis in its outer regions. Which anatomical sub-zone of the cortex is specialized for this dual requirement?
Explanation: In a young dicot stem, the cortex consists of three sub-zones. The outermost sub-zone is the hypodermis, which consists of a few layers of collenchymatous cells just below the epidermis. Collenchyma is a living mechanical tissue that provides essential mechanical strength to the young growing stem while retaining extensibility and elasticity.
Question 27 of 115
📘 CLASS XI
If a plant physiology lab stains a transverse section of a young dicot stem with a dilute iodine-potassium iodide (IKI) solution, which specific anatomical layer of the cortex will show a distinct, dark blue-purple ring?
Explanation: The innermost layer of the cortex in a dicot stem is the endodermis. The cells of the endodermis are uniquely rich in starch grains, and because of this storage characteristic, this layer is also referred to as the starch sheath. Iodine stains starch a deep blue-purple.
Question 28 of 115
📘 CLASS XI
If you trace a radial path from the outer protective surface to the absolute center of a primary dicot stem, passing directly through a vascular bundle, which sequence of tissues will you encounter?
Explanation: In a primary dicot stem, the layers from outside to inside are: the protective epidermis, followed by the cortex composed of collenchymatous hypodermis, rounded parenchymatous cortical cells, and the endodermis (starch sheath). Next is the pericycle (present on the inner side of the endodermis as semi-lunar patches of sclerenchyma above the phloem). Then comes the conjoint open vascular bundle containing phloem, cambium, and xylem. Finally, the central region is occupied by the pith.
Question 29 of 115
📘 CLASS XI
What is the main structural composition and primary physiological role of the medullary rays in a primary dicotyledonous stem?
Explanation: In between the vascular bundles of a young dicot stem, there are a few layers of radially placed parenchymatous cells, which constitute the medullary rays. Because they are parenchymatous and extend radially between the pith and the cortex, their primary function in the stem is lateral (radial) translocation of water and organic solutes.
Question 30 of 115
📘 CLASS XI
A botany student examines a vascular bundle slide under a microscope and notes that the earliest-formed xylem (protoxylem) points toward the center of the stem, whereas the later-formed xylem (metaxylem) points toward the outside. What is this xylem arrangement called?
Explanation: In dicot and monocot stems, the protoxylem lies towards the center (pith) and the metaxylem lies towards the periphery. This specific developmental arrangement of primary xylem is called endarch.
