Believed to be the best photosynthetic eukaryotes, algae are found in water and form a group of protists that are of great biological importance to humans. Algae lack true stem, roots and leaves and therefore, are given the special name thallus. Spread throughout intertidal zone, most algae have specialized adaptations for protection against drying when exposed during low tide. Some large algae, like kelps, are edible and considered staple food in some par of the world. Extracts from kelp and other algae used to produce products like ice cream and cosmetics.
Algae are differentiated according to the presence of photosynthesis pigments
(a) Green algae: Appearing as single-celled amorphous sheets or a collection of long filamentous strands, green algae belong to phylum Chlorophyta category. Most species are found in fresh water habitats even as they can survive in marine waters, damp soils, snow and ice. (b)Red algae: Belong to phylum Rhodophyta group, red coralline algae can incorporate calcium carbonate into their cell walls, thereby, lending their body a rigid, segmented appearance and texture. Most of these species have the ability to carry out photosynthesis at much greater depths than other types.
(c)Brown algae: These are multicellular algae (such as kelps), which can have leaf-like blades and stems and grow in marine waters near the coast. And due to the presence ef pigment fucoxanthin, their texture is of brown or olive colour.
(d) Diatoms: Significant components of phytoplankton, diatoms are tiny, floating, photosynthetic organisms that form the base of aquatic food chains. They are single-celled algae with a cell wall made of silica or glass.
(e)Golden brown or yellow brown algae: Alike brown algae, this category too receives its characteristic colour from the carotenoid pigment fucoxanthin. Usually, they are unicellular and colonial and swim or float in lakes and oceans as phytoplankton.
(f)Blue-green algae: Probably the most ancient organisms on Earth, blue-green algae are also called as cyanobacteria. They are single-celled and connect in a filament form or are arranged in simple colonies.