Life Cycles of nonflowering plants

1. Life Cycles of nonflowering plants

2. Like the algae they evolved from, non­flowering plants have a life cycle made up of two different stages.

3. plants alternate between a sexual stage and a nonsexual stage.

4. In the sexual stage, a plant called the gametophyte (guh MEET uh FYT) produces egg and sperm cells.

5. The sperm and egg combine to form a fertilized egg cell, which grows into an embryo.

6. The embryo grows into a sporophyte(SPOR roh FYT), the plant that makes up the nonsexual stage.

7. The sporophyte produces spores. A spore is a nonsexual reproductive cell with a protective coat.

8. A spore develops into a gametophyte. The gametophyte reproduces sexually, and the cycle continues.

9. Some plants have separate male and female gametophytes.

10. In other plants, one gametophyte produces both eggs and sperm.

11. This two-stage life cycle evolved in a water environment, where water was a means of transport for the sperm.

12. The gametophyte could live independent of the sporophyte.

13. A few land plants have this arrangement. They must rely on rainwater for transporting sperm, limiting where they can live.

14. Other plants adapted more completely to land by modifying their sexual stage.

15. It became shorter, and the gametophytes became smaller. These two changes allowed the sporophyte to evolve ways of protecting the gametophyte and helping the eggs and sperm to come together without water.

16. In the most complex nonflowering plants, the gymnosperms, the sexual stage takes place almost completely within the sporophyte.

17. This adaptation was made possible in part by the evolution of the seed. A seed is made up of an embryo, a stored energy supply, and a protective seed coat .

18. End