Pollen Structure & Sporopollenin — NEET Biology
✅ Asked in NEET 2024Pollen 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. The exine exhibits a fascinating array of patterns and designs. Why do you think the exine should be hard? What is the function of germ pore? The inner wall of the pollen grain is called the intine. It is a thin and continuous layer made up of cellulose and pectin. The cytoplasm of pollen grain is surrounded by a plasma membrane. When the pollen grain is mature it contains two cells, the vegetative cell and generative cell. The vegetative cell is bigger, has abundant food reserve and a large irregularly shaped nucleus. The generative cell is small and floats in the cytoplasm of the vegetative cell. It is spindle shaped with dense cytoplasm and a nucleus. In over 60 per cent of angiosperms, pollen grains are shed at this 2-celled stage. In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed (3-celled stage).
NTA focuses on why sporopollenin in the exine makes pollen well-preserved as fossils. Sporopollenin is extremely resistant to heat, acids, and alkalis, and no enzyme degrades it—this exceptional durability allows pollen to survive millions of years in geological layers. Students often confuse the exine (hard outer layer) with the intine (soft inner layer made of cellulose and pectin), or forget that germ pores lack sporopollenin, making them the weak points. Remember: sporopollenin's resistance = fossil preservation; exine = protection; intine = flexibility during germination. This concept appears because understanding pollen structure is fundamental to plant reproduction and paleobotany.
This paragraph was tested 2 times in NEET.
Pollen grains remain preserved as fossils due to the presence of:
Which of the following has proved helpful in preserving pollen as fossils? (NEET 2018)
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