Under a microscope, you observe a primary stem containing scattered vascular bundles. Each bundle is closed and conjoint. What can you conclude about the potential of this stem to undergo secondary growth?
Explanation: Scattered conjoint closed vascular bundles are a hallmark feature of monocotyledonous stems. Because these bundles have no cambium present in them, they do not form secondary tissues and are referred to as closed. Thus, secondary growth is impossible.
Question 92 of 115
📘 CLASS XI
Why are the tangential and radial walls of the root endodermis deposited with a waxy, water-impermeable material called suberin?
Explanation: The root endodermis has a deposition of water-impermeable, waxy suberin in the form of Casparian strips on its tangential and radial walls. This waterproof barrier blocks the passive, unregulated passage of water and dissolved minerals through the cell walls (apoplast), forcing them through the living cell membranes (symplast) to regulate what enters the xylem.
Question 93 of 115
📘 CLASS XI
How does the arrangement of primary xylem elements differ between a primary root and a primary stem?
Explanation: In roots, the protoxylem lies towards the periphery and the metaxylem lies towards the center, which is an exarch arrangement. In stems, the protoxylem lies towards the center and the metaxylem lies towards the periphery, which is an endarch arrangement.
Question 94 of 115
📘 CLASS XI
If a mutation blocks the development of companion cells in an angiosperm, which other tissue element of the vascular system will be directly impaired functionally, and why?
Explanation: Phloem is a complex conducting tissue composed of sieve tubes, companion cells, phloem parenchyma, and phloem fibers. Sieve tube elements are living conducting cells that lack a nucleus at maturity; their physiological activity and pressure gradients are maintained and regulated by the closely associated companion cells.
Question 95 of 115
📘 CLASS XI
Why are the cells of the root endodermis shaped like barrels and packed compactly without any intercellular spaces?
Explanation: The endodermis of a root comprises a single layer of barrel-shaped cells without any intercellular spaces. This tightly packed, gap-free arrangement ensures that water and solutes cannot bypass the endodermal barrier via the cell walls, forcing them through the selectively permeable cell membranes to reach the vascular cylinder.
Question 96 of 115
📘 CLASS XI
What is the structural significance of the 'ring' arrangement of vascular bundles in a dicotyledonous stem?
Explanation: The 'ring' arrangement of vascular bundles is a characteristic of the dicot stem. This spatial organization distributes the conjoint open vascular bundles symmetrically around the central pith, separated by radial medullary rays. This setup is essential for forming a continuous, functional vascular cambium ring during secondary growth.
Question 97 of 115
📘 CLASS XI
In a monocotyledonous stem, what is the spatial relationship between the size of the vascular bundles and their proximity to the epidermis?
Explanation: In a monocot stem, the vascular bundles are scattered throughout the ground tissue, but they show a specific size gradient: peripheral vascular bundles are generally smaller than the centrally located ones.
Question 98 of 115
📘 CLASS XI
In a grass leaf, which specific epidermal cells undergo anatomical modification along the veins to prevent excessive transpirational water loss under water stress?
Explanation: In grasses, certain adaxial epidermal cells along the veins modify themselves into large, empty, colourless cells called bulliform cells. When they lose water and become flaccid due to water stress, they cause the leaves to curl inward to minimize transpirational water loss.
Question 99 of 115
📘 CLASS XI
What tissue lies between the xylem and phloem in a conjoint open vascular bundle, and what biological capacity does it provide?
Explanation: In conjoint open vascular bundles (characteristic of dicot stems), cambium is present between phloem and xylem. This lateral meristematic tissue possesses the ability to form secondary xylem and phloem tissues, which is the basis for secondary growth.
Question 100 of 115
📘 CLASS XI
If you are comparing the ground tissue of a leaf (mesophyll) in monocots and dicots, what is the fundamental structural difference?
Explanation: In a dorsiventral (dicot) leaf, the mesophyll is differentiated into palisade parenchyma and spongy parenchyma. In an isobilateral (monocot) leaf, the mesophyll is not differentiated into palisade and spongy parenchyma; it consists of uniform chlorenchymatous parenchyma.
