Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Sporopollenin
The pollen grain wall has two layers. The hard outer layer, the exine, is made of sporopollenin. It withstands high temperatures and strong acids and alkali, and no enzyme that degrades it is known so far. This is why pollen grains are well preserved as fossils.
Option (1) Suberin — Incorrect. Suberin is not mentioned for the pollen wall in NCERT. The exine is made of sporopollenin.
Option (2) Cellulose — Incorrect. Cellulose is found in the inner wall, the intine, along with pectin, not in the exine.
Option (3) Sporopollenin — Correct. The exine is made of sporopollenin, one of the most resistant organic materials known.
Option (4) Pectin — Incorrect. Pectin, like cellulose, is a component of the intine.
NCERT Extract:
Stamen, Microsporangium and Pollen Grain – “… 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.”
Stamen, Microsporangium and Pollen Grain – “… The inner wall of the pollen grain is called the intine. It is a thin and continuous layer made up of cellulose and pectin.”