Types of life cycle in algae- Haplontic, Diplontic, Haplobiontic, Diplohaplontic for Bsc and Msc with Notes

 

• Life cycle is the sequence of changes in morphological phases during the growth and development of organism.
• A life cycle with two generations- Sporophyte and Gametophyte is called as Alteration of Generation.
• When the Gametophyte does not resemble the Sporophyte, this is called as Heteromorphic Alteration of Generation.
• When the Gametophyte resemble the Sporophyte this is called as Homomorphic Alteration of Generation.
• Sporophyte are always diploid with cells capable of undergoing Meiosis and form Haploid spores.

On the basis of occurrence of haploid and diploid phase alternating with each other five types of cycles :

• Haplontic
• Diplontic
• Diplohaplontic
• Haplobiontic
• Diplobiontic

Haplontic Life Cycle

• In this type of life cycle the vegetative plant is haploid/ Gametophyte.
• Haploid gametes are produced by male and female Gametophyte.
• Gametes unite to form diploid zygote or Sporophyte.
• The sporophyte produces haploid spores by MEIOSIS.
• These haploid spores give rise to gametophyte(haploid)
• Thus there is alteration of haploid gametophytic phase and single celled diploid phase.
• Example: Chlorophyceae

Diplontic Life Cycle

• In this type of life cycle the vegetative plant is diploid/ Sporotophyte.
• Sex organs are produced on diploid sporophyte.
• They undergo meiosis to form haploid gametes.
• Two haploid gametes fuses to form diploid zygote.
• Diploid zygote divide by mitosis to sporm diploid sporophyte.
• Here the diploid phase is shortest and only represent by gametes.
• Example : In Fucus

Diplohaplontic Life Cycle

• In this type of life cycle there are two vegetative phase represented by easily visible sporophyte and gametophyte.
• Gametophyte plant body produces haploid gametes.
• Sporophyte plant body produces haploid spores which germinate to form haploid plant body
• Example: Ectocarpus

Haplobiontic Life Cycle

• In this type of life cycle haploid phase occurs twice.
• Gametophyte produces haploid gametes that fused to form diploid zygote.
• Diploid zygote undergo meiosis to form haploid cells that form another haploid vegetative individual called as CARPOSPOROPHYTE.
• This haploid carposporophyte is attached to parent gametophyte and obtain its nourishment.
• Carposporophyte produces haploid carpospores which form gametophyte body.
• The sporophytic phase is only restricted to zygote.

Diplobiontic Life Cycle

• In this type of life cycle diploid phase occurs twice.
• Gametophyte produces gametes that fuses to form diploid zygote.
• Diploid zygote undergo mitosis to form diploid CARPOSPOROPHYTE which lives on parent body.
• The diploid produces haploid carpospores in carposporangia which germinate to form diploid body- Tetrasporophyte.
• Tetrasporophyte produces Tetraspores by meiosis.
• Haploid tetraspores germinate to form gametophyte plant.
• Example: Polysiphonia