Life Cycle Patterns of Algae (5 Types of Life Cycle in Algae)

In this article we will discuss about 5 life cycle patterns of algae (Life Cycle in Algae):- 1.Haplontic life cycle, 2.Diplontic life cycle, 3.Diplohaplontic life cycle, 4.Haplobiontic life cycle and 5.Diplobiontic life cycle

Types of Life Cycle in Algae

• The sequence of events through which one generation passes into the next generation is called life cycle.
• Sexual reproduction involves alternation between haploid and diploid generation which we call alternation of generation.
• In algae, there are five main types of life cycles or alternation of generation: haplontic life cycle, diplontic life cycle, diplohaplontic life cycle, haplobiontic life cycle and diplobiontic life cycle

1. Haplontic Life Cycle in Algae

• The haplontic life cycle is the simplest and most primitive life cycle pattern observed in some algae, particularly unicellular and filamentous forms.
• In this life cycle, the dominant and visible phase is the haploid gametophyte.
• Haploid gametophyte produces gametes through mitosis, which then fuse during sexual reproduction to form a diploid zygote.
• The zygote undergoes meiosis to produce haploid spores, which develop into new haploid individuals.
• Zygotic meiosis occurs, with no formation of a sporophytic thallus (diploid).
• E.g. Chlamydomonas, Oedogonium and spirogyra

2. Diplontic Life Cycle in Algae

• The diplontic life cycle is commonly found in higher plants but is also observed in certain algae. In this life cycle, the dominant and visible phase is the diploid sporophyte.
• The diploid sporophyte produces gametangium.
• In gametangium, the male and female gametes produced by meiosis.
• The gametes undergo syngamy to produce a diploid zygote.
• The zygote germinate into the sporophytic plant.
• The sporophytic plant will later undergo meiosis to produce the gametes.
• E.g. diatoms (Bacillariophyceae), Dasycladiales (green algae) and Fucales, Sargassum (Brown algae)

3. Diplohaplontic Life Cycle in Algae

• True alternation of generation occurs.
• This type of life cycle that consists of two different vegetative individuals alternating with each other is called diplohaplontic.
• There are two types of diplohaplontic life cycles

I. Isomorphic

• The diploid sporophyte produces sporangia. The sporangial mother cells undergo meiosis and produce haploid meiospores.
• The meiospores germinate into haploid gametophytic thalli and here gametes are produced. The male and female gametes fuse together to form a diploid zygote (2N). It produces diploid sporophytic thallus.
• Alternating sporophyte and gametophyte are morphologically similar.
• E.g., Ulvales, Cladophorales, Ectocarpales, Dictyotales and red algae.

II. Heteromorphic

• Alternating generations are morphologically dissimilar.
• E.g., Laminarials, Desmarestiales etc

4. Haplobiontic Life Cycle in Algae

• In this life cycle two haploid generations alternate with one diploid generation (Triphasic life cycle).
• The two haploid generations are represented by the carposporophyte and the gametophyte.
• The diploid sporophytic phase is restricted to zygote (2N).
• The main plant body which is gametophyte produces gametes. These gametes fuse to form zygote that undergoes meiosis and develops into carposporophyte.
• Carpospores of carposporophyte germinates to form chatransia stage.
• Chatransia stage then develops into normal gametophyte.
• E.g. Batrachospermum (red alga), Nemalion

5. Diplobiontic Life Cycle in Algae

• In this life cycle one haploid generations alternate with two diploid generation.
• The main plant body is gametophyte that produces gametes.
• Zygote is formed by syngamy and differentiates into diploid carposporophyte.
• Diploid carposporangia develops in carposporophyte and diploid carpospores are produced within carposporangia.
• On liberation, carpospores develops into diploid tetrasporophyte.
• Tetraspores are produced after meiosis inside tetrasporangia.
• Tetraspores develop into main gametophytic plant thallus.
• E.g. Polysiphonia