BIOLOGY Volume 1 - A Guide to General Biology - 2004

2. THE DIVERSITY OF LIFE ON EARTH

2.7. The Plant Kingdom

2.7.7. Summary of seed plant adaptations to terrestrial life

The primary evolutionary advantages of seed plants over all other plant groups can be summarized as follows.

1. The gametophyte generation is highly reduced and entirely dependent on the well-adapted terrestrial sporophyte, within which the gametophyte remains permanently protected. In other plant groups, the gametophyte is extremely prone to desiccation.

2. Fertilization is independent of Water. Male Gametes are non-motile and are dispersed within pollen grains by wind or insects. The final delivery of male gametes to the female gametes is achieved via a pollen tube.

3. Fertilized ovules (seeds) remain attached to the parent sporophyte for a period, receiving protection and nourishment before being dispersed.

4. Many seed plants exhibit Secondary Growth with the accumulation of extensive secondary xylem (wood), which provides structural support. This enables them to evolve into trees and shrubs capable of competing effectively for light and other resources.

Some of The most significant evolutionary trends are summarized in Fig. 2.33. Seed plants also possess several other features that are not exclusive to this group, yet serve as vital adaptations to terrestrial life.

1. True roots ensure the efficient uptake of soil moisture.

2. Plants are protected against water loss by an epidermis covered with a waterproof cuticle (or by periderm, formed As a result of secondary growth).

3. The epidermis of aerial plant Organs, particularly leaves, is perforated by numerous microscopic pores called Stomata, which facilitate gas exchange between the plant and the atmosphere.

4. Plants also feature specialized adaptations for surviving in hot, arid environments (Chapters 19 and 20).