recap

28.1 recap

Today’s living seed plants fall into two major groups, the gymnosperms and the angiosperms. Pollen grains, seeds, and wood are major evolutionary innovations of the seed plants. Protection of embryos is a hallmark of seed plants.

learning outcomes

You should be able to:

  • Explain how the evolution of pollen enabled seed plants to thrive in terrestrial environments.

  • Summarize the major advantages of having seeds.

  • Explain how seed plants altered the terrestrial landscape.

Question 1

Explain the importance of pollen in freeing seed plants from dependence on liquid water.

Pollen grains are highly resistant to dehydration and can be carried by wind or pollinators. Once a pollen grain lands on a stigma of a flower, it can grow a pollen tube, from which it releases sperm directly to the megagametophyte.

Question 2

How do seeds and seed dormancy help plants survive in highly seasonal environments?

Seeds protect the embryo from excessive drying and from predators. Seeds can remain in a resting state in soil, often for many years, until conditions become favorable for growth. Many seeds also aid in dispersal by wind, water, or animals. When growth begins, the seed provides the developing sporophyte with the food reserves it needs.

Question 3

What part did the evolution of wood play in changing the terrestrial landscape?

Wood provided structural stability for the stems of plants and allowed them to reach great heights. The forests of the world are able to exist because of this evolutionary innovation.

The seed ferns have long been extinct, but the surviving seed plants have been remarkable successes. After the seed ferns, the gymnosperms were the next group of plants to dominate terrestrial environments.