Exine of pollen grains has prominent apertures where sporopollenin is absent are known as:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Germ pores
The pollen grain wall has two layers. The hard outer exine is made of sporopollenin, one of the most resistant organic materials known. At a few places the exine has openings with no sporopollenin; the pollen tube comes out through these.
Option (1) Intine — Incorrect. The intine is the thin inner wall of cellulose and pectin, not an opening in the exine.
Option (2) Germ pores — Correct. Germ pores are openings in the exine, and the pollen tube comes out through one of them when the pollen grain germinates.
Option (3) Vegetative cell — Incorrect. It is the bigger cell inside the pollen grain, with food reserves, which forms the pollen tube.
Option (4) Generative cell — Incorrect. It is the small cell that divides to give the two male gametes.
NCERT Extract:
Stamen, Microsporangium and Pollen Grain – “… Pollen grains are generally spherical measuring about 25-50 micrometers in diameter. It has a prominent two-layered wall. The hard outer layer called the exine is made up of sporopollenin which is one of the most resistant organic material known. It can withstand high temperatures and strong acids and alkali. No enzyme that degrades sporopollenin is so far known. Pollen grain exine has prominent apertures called germ pores where sporopollenin is absent. Pollen grains are well-preserved as fossils because of the presence of sporopollenin.”