Biology · Sexual Reproduction in Flowering Plants · NEET
The exine is the OUTER layer. It is the hard, protective layer made of sporopollenin. The intine is the INNER layer, which is thin and soft. Trick: 'EX' sounds like EXternal (outside), 'IN' sounds like INternal (inside). NEET often swaps these two to trap you.
The exine is made of sporopollenin. Sporopollenin is one of the most resistant organic materials known. It can survive high temperature and strong acids and alkalis, and no enzyme is known that can break it down. This is a very common one-line NEET fact.
Exine is the OUTER wall, hard, made of sporopollenin, and has germ pores. Intine is the INNER wall, thin and continuous, made of cellulose and pectin, with no germ pores. Exine protects; intine lies just below it around the cytoplasm.
Because it makes the exine almost indestructible. It withstands high temperature, strong acids and alkalis, and no known enzyme degrades it. This is why pollen grains are so well preserved as fossils. Remember: sporopollenin = fossil preservation + most resistant organic material.
Germ pores are prominent apertures (gaps) in the exine where sporopollenin is ABSENT. They are found only on the exine, not the intine. Their job: the pollen tube comes out through the germ pore during pollen germination. So germ pore = weak spot left on purpose for the pollen tube to exit.
The intine is made of cellulose and pectin. It is a thin and continuous layer. Note the pair: intine = cellulose + pectin. Students often wrongly write sporopollenin for intine; sporopollenin belongs to the exine only.
Because of sporopollenin in the exine. It resists decay, heat, acids and alkalis, and enzymes cannot break it. So the exine stays intact for a very long time, letting pollen survive as fossils. This links pollen structure to palynology, sometimes asked in NEET.
Which one of the following statements is not true?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Pollen grains are generally spherical and measure about 25 to 50 micrometres in diameter. Their shapes, colours and surface designs vary a lot between species.
Two layers. The outer exine (sporopollenin, with germ pores) and the inner intine (cellulose and pectin). Together this is called the sporoderm.
No. Germ pores are found only in the exine, where sporopollenin is absent. The intine is a thin, continuous layer with no pores.
The cytoplasm of the pollen grain is surrounded by a plasma membrane, which lies just inside the intine.
The exine is far more resistant because of sporopollenin. It survives heat, acids and alkalis and cannot be broken by known enzymes, so it is preserved in fossils. The intine is soft and easily degraded.
