Q5. List the four wall layers of a microsporangium from outside to inside, and say which of them help the anther to dehisce.
Epidermis, endothecium, middle layers, tapetum. The outer three protect the microsporangium and help in dehiscence of the anther to release the pollen; the tapetum nourishes the developing pollen grains (NCERT page 5).
Q6. Why are pollen grains well preserved as fossils?
Their exine is made of sporopollenin, one of the most resistant organic materials known: it withstands high temperatures and strong acids and alkali, and NCERT states that no degrading enzyme is known (page 7).
Q7. An ovary has 24 ovules. At least how many meiotic divisions are needed to form the embryo sacs and the pollen grains for all 24 ovules to be fertilised, assuming typical monosporic development and no pollen loss?
24 megaspore mother cells must divide, one per ovule. Each ovule needs one pollen grain, whose tube brings both male gametes, so 24 pollen grains are needed; one pollen mother cell gives 4, so 24 ÷ 4 = 6 pollen mother cells divide. The ideal minimum is 24 + 6 = 30 meiotic divisions (NCERT pages 6, 10 and 18).
Q8. Assertion: cleistogamous flowers produce assured seed-set. Reason: their anthers dehisce inside the closed flower, close to the stigma. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: pollen reaches the stigma inside the bud, so seeds set even in the absence of pollinators (NCERT page 12).
Q9. Which of these outbreeding devices prevents both autogamy and geitonogamy: monoecy, dioecy, or anther and stigma placed at different positions?
Dioecy, as in papaya: each plant is either male or female. Monoecy (castor, maize) and the different placing of anther and stigma prevent autogamy (NCERT page 15).
Q10. Explain the role of the tapetum in the formation of the pollen-grain wall. (NCERT Exercise 17)
NCERT says the tapetum, the innermost wall layer of the microsporangium, nourishes the developing pollen grains (page 5), and that the pollen’s outer wall, the exine, is made of sporopollenin (page 7). Beyond the NCERT text, the tapetum makes enzymes that free the microspores from their tetrads and synthesises precursors for the pollen wall (Yao, Hu and Yang, Seed Biology, 2022; CC BY 4.0), so the sporopollenin exine is built largely from materials supplied by the tapetum.