Why are blue-green algae called cyanobacteria?

Why are blue-green algae called cyanobacteria?
Question asked by @subha1900 on Twitter. 

Cyanobacterial Scum

It’s probably easier to explain this by asking the question the other way round: Why are cyanobacteria also called blue-green algae? The reason is that cyanobacteria appeared to look a lot like green algae when they were first discovered. We now know that they really are bacteria (prokaryotes). One criterium to distinguish cyanobacteria from true algae is that prokaryotes lack a whole bunch of organelles present in algae, plants and animals (eukaryotes). For example: they don’t have a Golgi apparatus! >:-(

Cyanobacteria Under Light Microscope 40x Mag

Cyanobacteria appear coloured because they contain the photosynthetic pigments chlorophyll (green) and photocyanin (blue). This means that they can produce their own food. Some cyanobacteria can also look red or pink due to the pigment phycoerythrin


Algal Bloom Observation Registry

Encyclopedia Britannica

UCMB Berkeley



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