A. The exine is made of sporopollenin. It is highly resistant to high temperature, strong acids, and alkalis. It cannot be degraded by any of the known enzymes. Hence, sporopollenin protects the pollen grain from damage.
B. Exine layer is discontinuous around the pollen, leaving a pore called germ pore through which pollen tube emerges.
C. Pollen banks store pollen grains for years. The stored pollen grains can be used in plant breeding programme.
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