BIOL 410 - How Seeds Arise

What are gymnosperms?

Gymnosperms are our first seed plants. Some of their derived traits include seeds, pollen, and internal fertilization.

What does a seed consist of?

• seed coat (integument) lignin and waxes, grown around megasporangium. new and derived trait

• Early seed = megaspore on inside

• Later seed = embryo on inside

How did the seed arise?

By the evolution of lignin growing around the megasporangium to create protection.

What does the megasporangium that developed a seed coat do with their megaspores?

They retain megaspores, gametophyte, and embryos in the seed inside the parent tree. This is internal fertilization.

What was the integument like in early gymnosperms?

It was incomplete, extensions of cells filled with lignin.

What was the integument like in late gymnosperms?

They were fused.

What is pollen?

A derived trait in gymnosperms. It is a microgametophyte with sperm protected inside a spore wall. It has wings for flying. Develops inside cone.

What makes the life cycle of SVPs different from Gymnosperms?

In SVPs, spore coats open to release spores. Gametophytes develop in water. In gymnosperms, microspores go through mitosis to make gametophytes (pollen), this is all happening inside the male cone. It is not released until the pollen grain is ready to be released.