Life cycle in Algae

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.

1. Haplontic Life cycle:

• 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 

2. Diplontic Life cycle:

• 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

3. Diplohaplontic Life cycle:

• 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