Chapter 19

The Three Life Cycles- Mitosis- Meiosis- Alteration of Generation

By: Bryan Eng, Raza Samimy, and Tony Li

Marsilea

Somatic Cells

Gametes• Gametes are haploid cells that combine to form a zygote, which

eventually develops into a new organism. The process of two gametes coming together is called fertilization. Gametes are produced by meiosis in animals but are produced by mitosis in plants and fungi.

• Spores are haploid cells in plants produced by the sporophyte (more on this in alternation of generations).

Fertilization (sperm and egg)

Mitosis and Meiosis• Haploid cells have one copy of each chromosome, while diploid cells have

two copies of each chromosome.• In mitosis, one cell divides into two cells with the same number of

chromosomes (both haploid or both diploid). In meiosis, one cell divides into four cells with half the number of chromosomes (diploid to haploid).

Mitosis Meiosis

YouTube video on Meiosis

Alternation of generation-The another type of life in plant and has diploid and haploid multicellular stages stages

-The diploid stage is called sporophyte ( meiosis in this -produces haploids called spores) and the haploid stage is called gametophyte( gametes are made by mitosis)

-Two haploids merger and fertilize to result as a zygote which develops into the next sporophyte and gametophyte generations.

-They take turns reproducing each other

Review Questions• How many daughter cells are produced by mitosis? By meiosis?• What is the process of two gametes coming together called?• In what organisms are gametes produced by mitosis? By meiosis?• What type of cell are spores (haploid or diploid)? What structure in plants

produces them?• What is the spore producing plant generation and what stage is it in?• What happens in the gametophyte?