The non-degradability of sporopollenin is attributed to:

The correct answer is Option (4) → All of the above

Sporopollenin makes up the hard outer wall of the pollen grain, the exine. It is one of the most resistant organic materials known. This is why pollen grains are well preserved as fossils.

Option (1) Its resistance at very high temperatures. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Sporopollenin can withstand high temperatures, so heat does not break it down.

Option (2) The absence of enzymes that can degrade it. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. No enzyme that degrades sporopollenin is known, so living organisms cannot digest it.

Option (3) Its ability to withstand strong acids. — Correct statement, but it is only one of the correct points, so on its own it is not the answer. Sporopollenin can withstand strong acids and alkali, so chemicals do not break it down either.

NCERT Extract:
Stamen, Microsporangium and Pollen Grain – “… 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.”