KCET · BIOLOGY · STD 12 - 1. Sexual Reproduction in Flowering Plants

During an excavation of soil, pollen fossils were retreived from deepest layer of soil. The pollen grains remained as fossils because

A pollen grains are asexual reproductive structures
B the intine of pollen grains is made up of pectin
C exine has spiny ornamentation
D the exine of pollen grains is highly resistant to enzyme action

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(D) the exine of pollen grains is highly resistant to enzyme action

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(D) the exine of pollen grains is highly resistant to enzyme action,
Pollen grains have prominent two/three celled 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 temperature and strong acids and alkali. No enzyme that degrades spporopollenin is so far known. That makes pollens well preserved as fossils.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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