Powerpoint: Plant Reproduction Trends

• Define Alternation of Generation
• Describe the evolutionary trends of plant reproduction

One of the signature features of plants is that they reproduce via alternation of generations. Alternation of generations happen when in one complete life cycle, both asexual and sexual reproduction occurs. This is also accompanied by both haploid and diploid life stages.

In most plant life cycles (other than unicellular algae), there will be multicellular haploid and diploid stages.

We call the multicellular diploid stage the sporophyte. In ferns, gymnosperms and flowering plants, the sporophyte stages are the obvious stages. For example, the fern and trees are the sporophyte stage.

The purpose of the sporophyte:

• To produce spores via meiosis
  • The spores, unlike the diploid multicellular stage are haploid 
• To help the plant to disperse

The haploid spores will then duplicate to become the haploid, multicellular gametophyte.

The purpose of the gametophyte:

• To produce gametes (eggs and sperm) by mitosis
• These gametes can then be used for sexual reproduction.
• Sexual reproduction creates new combinations of genes that may produce new traits better suited to the environment. They also provide a better chance at least some may survive.

When the haploid gametes (N) fuse, they create a single diploid (2N) cell called a zygote. This zygote will then duplicate and become a multicellular diploid organism: the sporophyte.