7.03 Honors: Alternation of Generations

The Honors student will:

• define alternation of generations and its importance to the survival of plant species
• identify the basic stages of alternation of generations

Ready for a little more research on plant reproduction? There are a few more things we need to know before we make our decision on which plants will be BioDome plants.

Alternation of Generations

You should recall that plants are classified in a variety of ways. One of the ways they are grouped is according to their methods of reproduction. Regardless of their reproductive style, one thing that all plants have in common is that they go through alternating life stages. We call this alternation of generations.

There are some terms that will help you understand this material:

• gametophyte generation—produces gametes (sex cells)
• sporophyte generation—produces spores

Non-seed plants, like ferns, have a dominant sporophyte generation that produces spores with a hard outer covering. After they are released and land in a hospitable environment, they can develop into new plants, which can make more spores. The adult plant in this case is called a sporophyte.

Notice the round structures on the fronds from a fern plant. These are the spore cases. Each one contains many spores.

Seed plants, like the orchids we've been studying, have a dominant sporophyte stage. The sporophyte stage of seed plants is the plant as a whole or what we see. The flower contains the gametophyte parts of the plant that produces the gametes for reproduction.

Diagram of Alternation of Generation in Plants

Text-only Version

Note: For most plants, the sporophyte generation is the adult plant you are familiar seeing. For example, when you look at an oak tree you are seeing the sporophyte.

SAS inSchool Web Activity

1. Go to: http://www.sasinschool.com/login.
2. Enter the user name: flvs.
3. In the Quick Launch box, enter: 48.

Instructions:

• Follow all procedures in the SAS lesson.
• For this activity we have modified the Respond Sheet in the following way:
  
  • Questions 1, 2, and the table that goes with #2 will be the only two items you need to complete.
  • You will find these in the printable version of the Alternations of Generations Respond Sheet below. Use this copy, not the one in the web activity.
• Otherwise read carefully and take notes for your Travel Log.

Printable copy of the Respond Sheet: Alternation of Generations Respond Sheet