Pollengrain contains an outer wall called exine. it is most resistant organic material nd can widstand high temperature. Due to the presence of sporopollenin pollen grains are preserved as fossils
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Pollen grains have a two-layered wall.and the hard outer layer is called as exine and is made up of sporopollenin which is the most resistant organic material . It can withstand the high temperatures, strong acids, alkali and etc.... there is no enzyme which degrades sporopollenin . Pollen grains are well-preserved as fossils because of the sporopollenin.

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