Blue Green Algae
Blue green algae are also known as blue algae, blue-green bacteria, cyanobacteria or Cyanophyta. They are found in the phylum Cyanobacteria in the domain Bacteria and are a type of bacteria that produces their own energy from sun-light through photosynthesis, just like algae and plants do.
Cyanobacteria have traditionally been considered a type of algae, but recent works on algae usually exclude them since there are such significant differences between cyanobacteria and all the other traditional algae. A cyanobacterium has a single circular chromosome, peptidoglycan (a polymer consisting of sugars and amino acids) is present in its cell walls, and there are no membrane-bound organelles. Instead of chloroplast, the cyanobacterium carries out photosynthesis on thylakoid membranes.
The main similarity between cyanobacteria and algae is that they both live in water and make their own food from sunlight. Cyanobacteria are however more closely related to other bacteria than to eukaryotes such as algae.
Geographical distribution and habitat
Blue green algae are found all over the world and can survive in a long row of different habitats. They are present in saltwater, brackish water and freshwater, and they can also occur in damp land habitats, e.g. in soil and on rocks. You can even find blue green algae growing on temporarily moistened rocks in the desert and in the fur of sloths. A majority of the species live in freshwater.
Some blue green algae live inside other organism. They form symbiotic relationships with other organisms and live as endosymbionts. An endosymbionts is an organism that lives inside the body or cells or another organism. Blue green algae are known to enter into this type of symbiotic relationships with sponges, lichens, plants and various protists, and provide their host with energy.
Forms and appearance
Each individual cyanobacterium cell will typically be protected by a thick, gelatinous cell wall. The cell has no flagella to propel itself with, but some species can move around by gliding over surfaces while others move around in water by forming gas vesicles.
Some species of blue green algae form colonies and can therefore appear in the form of sheets, filaments or hollow balls. Some filamentous colonies are so advanced that they contain more than one cell type and are capable of adapting their cell production to the environment. The colony can for instance produce akinetes, a special type of highly resistant spores capable of surviving in harsh environments. Many species of blue green algae can spread to new places by forming motile filaments.
The name cyanobacterium is derived from the word κυανόςwhich means “blue” in Greek. The blue-green colour of these bacteria is normally due to phycobiliproteins that are used to absorb light for the photosynthesis. Some cyanobacteria are instead looking more red-brown than blue-green, and such bacteria will typically contain carotenoids and phycoerythrins. In some species, the colour of the bacteria will be affected by the colour of the light. Red light will cause the bacteria to produce more of the substances that make them look green, while green light will make them produce more of the substances that make them look red. By doing so, the bacteria can use the light more efficiently.
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