Algae are organisms containing chlorophyll, which occur in very large numbers in nature – mainly in water. Their size ranges from microscopic single-cell forms to multicellular forms, which can reach a length of approximately 100 meters. Unlike plants, algae do not have real roots, trunks/stems and leaves; moreover, there is also a lack of reproductive cells in the fertile structures.  Algae are classified in six phyla: Euglenophyta, Crysophyta, Pyrrophyta, Chlorophyta, Phaeophyta and Rhodophyta. They form the basis of the food chain in the water.