Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. Due to their ecology (life in or under water), their construction plan is simple compared to the land plants - they are not structured in roots, peduncles and leaves because all parts of the organism are able to take up nutrients by diffusion. Furthermore, they have no septum, because the water gives them enough buoyance. In the modern biological sciences, ten thousands of algae are known until now and the molecular phycologists separate already existing taxa into others, which means the number of known species is rising continuously.
By taking a look to the algae's photosyntetical pigments, one can distinguish between several main groups:
Chlorophyceae (Green Algae): Chlorophyll a & b
Cyanophyceae (Blue Green Algae): Chlorophyll a
Rhodophyceae (Red Algae): Phycocyanin, Phycoerythrin
Bacillariophyceae (Diatoms): Chlorophyll a & c
and many more ...
Of course, this is just one criterion how to generate an artificial system. There are other parameters, which will probably lead to another classification system
Algae produce hundreds of metabolites; a few of them are quite interesting for economical applications. Most of them belong to the so called secondary metabolites. Concerning their chemical structure, they often contain carbohydrates. Pigments (for instance carotenoids) or energy storage products like triglycerids are of special interest.
Carotenoids are built up of carbohydrate chains and can be distinguished between the carotenes and xanthophylls. The absorption spectrum is around 400 - 500 nanometres.
Triglycerids are ester derived from glycerol and three fatty acids. Triglycerides are also split into their components bia transesterification during the manufacture of biodiesel. The resulting fatty acid esters can be used as fuel in diesel engines. The glycerine has many uses, such as in the manufacture of food and in the production of pharmaceuticals.