Life cycle is the cyclic sequence of events occurring in the life of an organism. The different types of life cycles of algae are Diplontic , Haplontic type, Diplohaplontic type, Diplobiontic type and Haplobiontic.
- Plants are haploid
- The main vegetative plant body is gemetophytic and haploid(n).
- Diploid phase is only represented by zygote (2n)
- Chlamydomonas, Ulothrix, Oedogonium, Spirogyra
- Plants are diploid.
- Plant body: 2n and sporophytic sex organs are also 2n. By meiosis forms gametes.
- Haploid stage represented only during gamete formation.
- Bacillariophyceae, Sargassum, Fucus Phaeophyceae
- Both 1n and 2n plants are present. It is of two types.
- A)Isomorphic alternations of generation: If both are morphologically similar and shows alternation of generation.eg: Cladophora, Ectocarpus, Ulva
- B)Heteromorphic alternations of generation: Here 2n plant is large and macroscopic and in plant is microscopic Eg : Laminaria
4. Haplobiontic Life (Diphasic life cycle):
- 2 well developed haploid phases are present. Diploid phase represented only by zygote.
- haploid generation is represented by the independent gametophyte and the parasitic carposporophyte
- First haploid phase represented by gametophytic plant body, sex organs and gametes.
- Second haploid phase represented by gonimoblast filaments, carposporangia, carpospores and chantransia stage
- Also called as diphasic life cycle as two haploid phases are present
- Haplobiontic seen in Batrachospermum, Nemalion
5. Diplobiontic Life Cycle (Triphasic life cycle):
- one well developed haploid phases and 2 diploid phases also called as triphasic lifecycle
- First haploid phase represented by male and female gemetophytic plant body, sex organs and gametes
- First diploid phase is represented by zygote, gonimoblast filament, carposporangia and carpospores. All these together represent carposporophyte which depends on the gametophyte
- Second diploid phase represented by tetrasporophytic plant bearing tetrasporangia.
- Seen in Polysiphonia