The main difference between cyanobacteria and green algae is that green algae are a eukaryotic organism having a nucleus and membrane-bound organelles while cyanobacteria are prokaryotes having no nucleus and membrane-bound organelles.
Both cyanobacteria and green algae are photosynthetic organisms which have evolved from algae. Both synthesize their own food with the help of sunlight using carbon dioxide and water in the presence of chlorophyll, but both have many differences. The key difference is that cyanobacteria are prokaryotic organisms. They do not have membrane-bound organelles and true organelles while green algae is a eukaryotic organism which has a true nucleus and membrane-bound organelles.
Cyanobacteria are also known as blue-green algae. Cyanobacteria or blue-green algae does not have chloroplast in their cells while green algae do have chloroplast in their cells because they are eukaryotic organisms.
The term green algae are denoted to any green colored algae which are present in freshwater habitats. While the term cyanobacteria are denoted to photosynthetic bacteria that are found in the form of colonies which may be filamentous shaped, spherical or sheet-like. Under light microscopy, cyanobacteria show a homogenous color all across over the cell while green algae are able to be identified by the occurrence of chloroplast in the cell.
Some cyanobacteria are photoautotrophs, and some are heterotrophs (obtain their food from other organisms) while all the types of green algae are photoautotrophs, i.e., they prepare their own food using sunlight. Cyanobacteria perform nitrogen fixation. They use gaseous nitrogen as a nutrient source. On the other hand, green algae are not involved in nitrogen fixation.
Cyanobacteria have an efficient ability to store nutrients. On the other hand, green algae have less capability of storing nutrients. Cyanobacteria have not the ability to swimming, but they have the ability to change their buoyancy by changing their depth in water. Green algae have the ability of swimming in water.
Cyanobacteria reproduce asexually by cell division while the asexual reproduction of green algae takes place by budding, fragmentation, fission or by zoospores formation. Cyanobacteria do not reproduce by the sexual method, but green algae can reproduce sexually by the formation of gametes. The examples of cyanobacteria are Nostoc, Anabaena, and Oscillatoria, etc. While the examples of green algae are Chlamydomonas, Ulva and Spirogyra and chlorella, etc.
Comparison chart
| Basis | Cyanobacteria | Green algae |
| Definition | Cyanobacteria are also known as blue-green algae. They are actually photosynthetic bacteria which synthesize their food with the help of sunlight using CO2 and water. | They are a type of algae which is found in oceans and another water habitat. They also prepare their food by the process of photosynthesis |
| Prokaryote or Eukaryote | They are prokaryotic organisms | They are eukaryotic organisms. |
| Membrane-bound organelles and nucleus presence | Nucleus and membrane-bound organelles are not present in cyanobacteria | Nucleus and membrane-bound true organelles are found in green algae |
| Colonies | They are present in the form of colonies of different shapes like filamentous, sheet-like a colony or spherically shaped colony. | Green algae do not form colonies. |
| On light microscopy | By light microscopy, they show a uniform green color. | By light microscopy, they show a green colored chloroplast which is their point of identification. |
| Autotrophs or heterotrophs | Some types are photoautotrophs, and some are heterotrophs | All the types are autotrophs |
| The ability for storing nutrients | They have an efficient ability to store nutrients. | They have less ability to storing nutrients. |
| Nitrogen fixation | They have the ability to perform nitrogen fixation | They do not show nitrogen fixation |
| Swimming capability | They do not have the ability to swimming in the water, but they show buoyancy. | They do have the ability of swimming in water |
| Asexual reproduction | They reproduce asexually by simple division | They reproduce asexually by budding, binary fission, fragmentation or zoospores formation. |
| Sexual reproduction | They do not reproduce by the sexual method. | They can reproduce by the sexual method. They form gametes for this purpose. |
| Examples | The examples can be given as Nostoc, Anabaena, and Oscillatoria | The examples can be given as Chlamydomonas, Ulva, Spirogyra, and chlorella. |
What are Cyanobacteria?
Cyanobacteria are also called blue-green algae, but in reality, they are not algae. They are a type of bacteria which are prokaryotic organisms and do not have membrane-bound organelles and nucleus. They do not have chloroplast but the green pigment, chlorophyll is present in cyanobacteria which is mandatory for photosynthesis. They have the capability to synthesize their own food by using CO2 and water with the help of sunlight and chlorophyll. Cyanobacteria live in the form of colonies which are of different shapes, i.e., filamentous , spherical, circular, sheet-like or cord-like. These colonies do not show the division of labor among the individuals and each member of the colony itself fulfills all the tasks mandatory for life. On light microscopy, cyanobacteria appear as a uniform green color. They cannot reproduce by sexual mode of reproduction. They perform asexual reproduction by the simple division to produce next progeny. Some types of green algae are photoautotrophs while some are heterotrophs, i.e., they are dependant upon other organisms for food. Cyanobacteria also have the ability to do nitrogen fixation. They use nitrogen as a nutrient.
What are Green Algae?
They are a type of eukaryotic photoautotrophs that have the ability to prepare their own food by the process of photosynthesis using CO2 and water. Since they are eukaryotes, they have a nucleus and membrane-bound organelles. They do not form colonies. On light microscopy, a green colored chloroplast appears in green algae which id their point of identification. All the forms of green algae are autotrophs. They reproduce both by asexual and sexual mode of reproduction. For sexual reproduction, they form gametes. They reproduce asexually by budding, fragmentation, binary fission and by the formation of zoospores. They have less capability of storing nutrients opposite to blue-green algae. They can swim in the water.
Key differences
- Cyanobacteria are prokaryotic organisms while green algae are eukaryotic organisms. Both can do photosynthesis.
- Cyanobacteria reproduce asexually while green algae reproduce both by sexual and asexual methods.
- Cyanobacteria can do nitrogen fixation while green algae cannot fix nitrogen.
- Cyanobacteria may be autotrophs or heterotrophs while all the green algae are autotrophs.
- Cyanobacteria cannot swim while green algae can swim.
Conclusion
Both cyanobacteria and green algae are the organisms which can do photosynthesis. It is important for biology students to know the differences between them. In the above article, we came to know the clear differences between cyanobacteria and green algae.
