Oedogonium: a filamentous green algae
Oedogonium is representative of a number of organisms in a very diverse group, the green algae. In this book we consider several members of the green algae that illustrate a range in form and structure. The other members of the green algae group are Chlamydomonas (small and unicellular), Acetabularia (large and unicellular) and Caulerpa (large and coenocytic), which are quite different in form and structure.
Taxonomy and Phylogeny
The filamentous life form is not a good phylogenetic characteristic, i.e. it does not unify a group that is considered to be closely related. It is found in several of the subgroups (orders and families) of the green algae as well as in other protist phyla (brown and red algae), and even in some prokaryote groups. In an alternate and more phylogenetically based classification of the green algae group (presented in the write up for Chlamydomonas), Oedogonium is in the Chlorophyaceae, a diverse group of algae that are in the branch of green algae (Chlorophyta) that is not thought to contain the ancestor of land plants. Like most green algae, and like all plants, Oedogonium has both chlorophyll a and b, stores carbohydrates as starch and has cellulose cell walls.
Oedogonium forms elongate filaments of cells, most of which are non-flagellated, cylindrical and have a cell wall that contains both cellulose and chitin. These cells are vegetative, i.e. are not associated with reproduction but only associated with photosynthesis and growth of the filament. Several additional cell types are produced that bring about reproduction and sex:
- zoospores—mobile, flagellated cells do not have cellulose cell walls. Zoospores are released from parental cells and can attach to various substrates, becoming immobile and dividing to form new filaments. Zoospores have contractile vacuoles; why do you think this is the case?
- oogonia—large cells that develop a pore in the cell wall that allows flagellated sperm cells to enter the cell
- sperm—mobile, flagellated cells that are released from parental cells and swim to the oogonia
- zygospores—produced after sperm fertilize eggs, these cells developed a thick cell wall. They eventually undergo meiosis and break open to release flagellated zoospores.
Oedogonium reproduces asexually via mobile zoospores and sexually via sperm, oogonia and zygospores. Sperm are released from parental cells and are chemo-attracted to the oogonia that house an egg. A pore in the oogonium cell wall allows the sperm to enter the oogonium and fertilize the egg. Fertilization occurs and the oogonium develops a thick wall, forming a structure called a zygospore. Eventually the cell inside the zygospore undergo meiosis and haploid daughter cells are released as mobile zoospores, which, like the zoospores produced asexually, swim to a substrate and attach themselves and elongate into filaments.
Matter and energy
Oedogonium is a typical photoautotroph, using the energy of sunlight to synthesize carbohydrates from carbon dioxide and then using the carbohydrates as an energy source in cellular respiration and as building materials to synthesize a variety of biomolecules.
Oedogonium is common in in fresh water habitats. It is eaten by a variety of herbivores including fish, mollusks and other invertebrates.