Saturday, December 8, 2007

Concept 30.1

Q1: Contrast sperm delivery in seedless vascular plants with sperm deliver in seed plants.

A1: To have any chance of reaching the eggs, the flagellated sperm of seedless vascular plants must rely on swimming through a film of water, usually limited to a range of less than a few centimeters. In contrast, the sperm of seed plants are produced within durable pollen grains that can be carried long distances by wind or by animal pollinators. Although flagellated in some species, the sperm of most seed plants do not require water because pollen tubes convey them directly to the eggs.

Q2: What additional features of seed plants, not present in seedless plants, contributed to the enormous success of seed plants on land?

A2: The reduced gametophytes of seed plants are nurtured by sporophytes and protected from stress, such as drought conditions and UV radiation. Pollen grains have tough protective coats and can be carried long distances, facilitating widespread sperm transfer without reliance on water. Seeds are more resilient than spores, enabling better resistance to environmental stresses and wider distribution.

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