What are algae?
The algae are a large and diverse group of organisms that includes various taxonomic categories. They are located in the kingdom of the Protists. They are related to plants, since they are photosynthetic organisms , often aquatic, but their degree of organization is much more basic than that of higher plants.
They have a wide distribution in the world, they can be found in seas, fresh water and humid areas of the earth’s surface . Most algae are microscopic unicellular organisms, although some are multicellular and can grow to a large size by spreading to form filaments and crusts. They are characterized by having chlorophyll and other accessory pigments of the carotenoid type, such as fucoxanthins and phycobilins.
Kinds of algae
The three main types are:
-Chlorophyta (green algae) : they are common in various aquatic environments. Green algae are the base of the food chain in the sea, they constitute one of the main components of the phytoplankton it produces. They colonize all kinds of habitats : fresh and salt water, snow, land and trees. They have chlorophyll a and b in a similar proportion to that of higher plants. Some green algae are grown or harvested for human consumption, as they are an important source of protein. They are considered as the predecessors of the higher plants. Ex: Spirogyra, Scenedesmus .
-Rhodophyta (red algae) : these are mostly tropical marine species . They can photosynthesize at great depth due to the presence of pigments such as phycoerythrin and phycobilins. Most are multicellular, filamentous, or membranous. Some accumulate calcium carbonate on their surface; this makes them hard and brittle (coralline algae). They are of industrial importance because they produce substances such as agar, carrageenan and gellan (thickeners). Eg: Gelidium , Coralina rubens . Another example of red seaweed is Nori (scientific name: Porphyra tenera ), which is used to make sushi.
-Phaeophyta (brown algae) : They are mostly marine species. They owe their name to the presence of a pigment called fucoxanthin , which masks the other pigments and gives them their typical brownish-brown color. There are about 1500 species in this group. Example: Laminaria digitalia .
Other well-recognized groups of algae are:
-Chrysophyta (golden algae): Related to the previous ones, they are characterized by their golden color due to the presence of the carotenoids fucoxanthin. They are characterized by having chlorophyll a and c. They predominate especially in fresh water .
-Diatomeas : they are mostly unicellular algaealthough some form colonies ; one of its characteristic features is the presence of a silica coating. They are an important part of phytoplankton.
-Euglenophyta: flagellate freshwater protists. They present triple membrane chloroplasts , with chlorophyll a and b. These algae are mobile because they have flagella.
-Dinoflagellates: they are algae with red pigments , although some individuals in this group lack pigments and are heterotrophs. Along with some protozoa, they are responsible for toxic red tides.
-The commonly called blue-green algae , which used to be part of the group of cyanophytes, today are considered in a separate group within bacteria.