How Does Algae Reproduce

Algae are a primitive type of plants that only grow in aquatic environments. Three modes of reproduction occur in algae: vegetative reproduction, asexual reproduction, and sexual reproduction. Vegetative reproduction may occur in several ways such as cell division, fragmentation, hormogonia, adventitious branches, etc. Asexual reproduction mainly occurs by the production of spores. There are several types of spores as zoospores, aplanospores, endospores, etc. Several sexual reproduction modes can also be identified as isogamy, heterogamy, anisogamy, and oogamy. 

Key Areas Covered

1. What are Algae
     – Definition, Facts
2. How Does Algae Reproduce
     – Vegetative Reproduction, Asexual Reproduction, Sexual Reproduction

Key Terms: Asexual Reproduction, Gametes, Macroalgae, Microalgae, Sexual Reproduction, Spores, Vegetative Reproduction

What are Algae

Algae are small, non-vascular, non-flowering, aquatic plants, containing chlorophyll for photosynthesis. The plant body of algae is a thallus, and it is not differentiated into a true stem, root, leaves. Two types of algae can be identified as unicellular and multicellular algae. Unicellular algae are called microalgae while multicellular algae are called macroalgae. Cyanobacteria (blue-green algae), green, red, and brown algae are microalgae. Seaweeds such as kelp are macroalgae. They grow about hundred feet in length. Most algae are autotrophic, i.e., produce their own food through photosynthesis. Algae produce 70% of the oxygen in the atmosphere through photosynthesis.

Figure 1: Cyanobacteria

How Does Algae Reproduce

Three modes of reproduction can be identified in algae. They are vegetative reproduction, asexual reproduction, and sexual reproduction. Each mode of reproduction of algae is described below.

Vegetative Reproduction

1. Cell division or binary fission – Unicellular algae such as Chlamydomonas and Synechococcus undergo vegetative cell division by mitosis.
2. Fragmentation – The breakups of the thallus in multicellular, filamentous algae such as Spirogyra develop into new individuals.
3. Hormogonia – In blue-green algae, trichomes are segmented into hormogonia. Hormogonia are found in Ocsillatoria, Nostoc, and Cylindosporium.
4. Formation of adventitious branches – Adventitious branches formed in large thalloid algae such as Fucus and Dictyota are detached from the main plant body, growing into new individuals. Protonema-like adventitious branches are formed in Chara and Cladophora.
5. Bulbils – Bulbils are tube-like outgrowths that store food. They grow into new individuals as in Chara.

Asexual Reproduction by  Production of Spores

1. Zoospores – Motile, naked spores of Chlamydomonas, Ectocarpus, Ulothrix, etc.
2. Aplanopores – Non-motile spores of Chlorella, Scenedesmus, Sphaerella, etc. produced under unfavorable conditions
3. Tetraspores – Haploid aplanospores of Polysiphonia that germinate to form male and female gametophytes
4. Akinetes – Elongated, thick-walled, spore-like vegetative cells of filamentous algae, which contain stored food
5. Exospores – Separated spores at the distal end of the protoplasm of Chamaesiphon
6. Endospores – Divisions of the protoplast, forming conidia or gonidia

Sexual Reproduction

All algae except Cyanophyceae show sexual reproduction. Depending on the mode of fusion, several methods of sexual reproduction can be identified.

1. Autogamy – Fusion of gametes produced by the same mother algae
2. Hologamy – Fusion of gametes from the different strains (+ and – strains)
3. Isogamy – Fusion of gametes that are both morphologically and physiologically similar
4. Anisogamy – Fusion of gametes that differ both morphologically and physiologically
5. Oogamy – Fusion of gametes motile male gametes and non-motile female gametes

Conclusion

Algae are primitive aquatic plants that show three modes of reproduction. They are vegetative reproduction, asexual reproduction, and sexual reproduction. Vegetative reproduction is the propagation through the vegetative parts of the plant body. Asexual reproduction occurs by the production of spores while sexual reproduction occurs through the fusion of gametes.

Reference:

1. “Reproduction in Algae: 3 Modes.” Biology Discussion, 24 Aug. 2016, Available here.

Image Courtesy:

1. “CyanobacteriaLamiot2009 07 26 290” By Lamiot – Own work (CC BY-SA 3.0) via Commons Wikimedia