You are given two unlabeled slides of angiosperm stem cross-sections: Slide A shows vascular bundles arranged in a distinct concentric ring, while Slide B shows numerous vascular bundles scattered throughout a large ground tissue. What can you conclude?
Explanation: According to NCERT, the ring arrangement of vascular bundles is a diagnostic characteristic of the dicotyledonous stem. Conversely, the monocotyledonous stem is characterized by a large number of scattered vascular bundles distributed through a conspicuous ground tissue.
Question 32 of 115
📘 CLASS XI
How does the mechanical support system of a monocotyledonous stem hypodermis differ from that of a dicotyledonous stem hypodermis?
Explanation: In a young dicot stem, the hypodermis consists of a few layers of collenchymatous cells. In contrast, the monocot stem has a sclerenchymatous hypodermis. Sclerenchyma provides highly rigid, non-elastic mechanical support, which is vital for monocots that do not undergo secondary timber formation.
Question 33 of 115
📘 CLASS XI
What is the structural significance of the sclerenchymatous bundle sheath found in monocotyledonous stems?
Explanation: In a monocot stem, vascular bundles do not form a consolidated ring; instead, they are scattered. To maintain structural integrity under mechanical stress, each scattered vascular bundle is surrounded by a protective sclerenchymatous bundle sheath.
Question 34 of 115
📘 CLASS XI
If you analyze the relative sizes of the scattered vascular bundles across a transverse section of a monocotyledonous stem, what spatial pattern will you observe?
Explanation: In a monocot stem, the vascular bundles are not uniform in size across the cross-section; the peripheral vascular bundles are generally smaller than the centrally located ones.
Question 35 of 115
📘 CLASS XI
A chemical analysis of the complex conducting tissues in a stem reveals the presence of sieve tubes, companion cells, and phloem fibers, but a total absence of phloem parenchyma. This tissue profile belongs to:
Explanation: A key diagnostic distinction of the monocotyledonous stem is that phloem parenchyma is absent. In dicotyledonous stems, phloem parenchyma is present and functions normally in food storage and translocation.
Question 36 of 115
📘 CLASS XI
During dry spells, some xylem vessels in certain plant stems can collapse or experience cavitation. To counter water transport disruptions, monocot vascular bundles possess a unique anatomical modification. What is this structure?
Explanation: Within the vascular bundles of a monocotyledonous stem, water-containing cavities are present. These cavities function as reservoirs and facilitate uninterrupted lateral water movement within the closed conjoint bundle.
Question 37 of 115
📘 CLASS XI
If you are preparing a comparative chart of angiosperm stems, which of the following features would be listed as completely absent in a monocotyledonous stem?
Explanation: In a dicot stem, the ground tissue is organized into highly distinct zones: cortex, endodermis, pericycle, medullary rays, and pith. In a monocot stem, there is no such division; instead, there is a large, conspicuous, undifferentiated parenchymatous ground tissue in which vascular bundles are scattered.
Question 38 of 115
📘 CLASS XI
Why does a sunflower stem increase in girth (undergo secondary growth) over successive seasons, while a maize stem remains relatively constant in diameter?
Explanation: Sunflower (a dicot) has conjoint open vascular bundles because cambium is present between its phloem and xylem, giving it the ability to form secondary tissues. Maize (a monocot) has conjoint closed vascular bundles because no cambium is present, preventing any secondary growth.
Question 39 of 115
📘 CLASS XI
Compare the structural distribution of sclerenchyma in the ground and vascular systems of dicot and monocot stems. Which of the following is correct?
Explanation: In a dicot stem, sclerenchyma is restricted to semi-lunar patches in the pericycle located on the inner side of the endodermis and above the phloem. In a monocot stem, sclerenchyma forms the hypodermis and the protective bundle sheath surrounding each scattered bundle.
Question 40 of 115
📘 CLASS XI
In a transverse section of a dicot stem, what constitutes the semi-lunar patches located on the inner side of the endodermis and directly above the phloem?
Explanation: NCERT states that 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.
