Question

Pollen and seeds are considered among the most advanced characteristics in the plant kingdom. DESCRIBE the evolutionary advantage(s) that each of these offer relative to what existed before - the plesiomorphic state (this means compare it directly as in x has ... while y has... and that is advantageous because...?)

Please answer the question in the form given. Thank you!

Answer 1

Bryophytes and pteridophytes have male gametophyte that released sperms in water. They have no protective covering and were subjected to desiccation, predation etc. Whereas, the seed plants have sporophyte generation in dominant phase. The pollen grains released by male reproductive organ are encased in a protective coat. The exine is made of spropollenin which is water proof. Thus, pollen grains are more advantageous as they don't depend on water for transfer and are resistant to mechanical stress. They can survive for long than the sperm counterparts.

In primitive plants, the sporophyte developes sporangia which undergo meiosis to form spores. These spores germinate and form gametophyte when conditions are favourable. Since, they don't have any prominent covering, they get destroyed under harsh environments. On the other hand, advanced plants form the seed that carries the embryo. It is advantageous as it provides nourishment and protection to embryo. Also, it could remain dormant for many years and germinate only when conditions are optimal.