ALGA


Meaning of ALGA in English

plural Algae, or Algas, any of a group of chiefly aquatic, nonvascular, photosynthetic, and eucaryotic organisms of the kingdom Protista. They range in size from one-celled flagellates measuring as little as 1 micron (one millionth of a metre) to the giant kelp reaching a length of 60 m (200 feet). Some authorities continue to classify the algae as plants or plantlike organisms, although they lack true leaves, stems, roots, and vascular systems, a feature they share with bryophytes (compare bryophyte). Algae may have from one to a few cells or may have tissuelike aggregations of cells. Filamentous forms may be branched (e.g., Sticheoclonium) or unbranched (e.g., Spirogyra). Some algae are single-celled flagellates (e.g., Oochromonas), while others (e.g., Scenedesmus) aggregate into colonies. Codium, the green seaweed, has a tissuelike appearance but is not separated into different cells. Although primarily aquatic, algae are ubiquitous, inhabiting regions from the forests of the temperate zones to the Arctic tundra. Some varieties live in soil and withstand long periods without water; others live in snow, and a few species thrive in hot springs. Algae share such eucaryotic cellular features as a nucleus and membrane-bound vacuoles and organelles (such as mitochondria). The majority of algae are aerobic, requiring oxygen for their life processes. Photosynthesis is carried out using the various chloroplast molecules, such as chlorophyll, carotenoids, and phycobiliproteins. Ninety percent of all photosynthesis on the Earth is carried out by algae, and it is believed that they played an important role in creating the Earth's oxygen-rich atmosphere early in the planet's history. Planktonic algae are an essential link in the food chain in the oceans, and all higher aquatic life-forms ultimately depend on it. In addition, algae have been used as feed for livestock and as food for human consumption since prehistoric times. Algae is used for a wide range of commercial purposes. Among its products is a form of gelose (e.g., agar) that is produced by more than 70 species of red algae. Agar is used in the canning of fish and the packing of cooked fish, to size fabric, in the manufacture of film and high-grade adhesives, and in soups, sauces, jellies, ice creams, and icings. The uses of carrageenan extracts (a product of Irish moss) parallel those of agar and also include the making of sodium, potassium, or calcium salts. Algenic acids, a constituent of brown algae, produce alkali salts that are spun like silk to make threads. Algae can reproduce vegetatively (through cell division or fragmentation), asexually (through the release of motile zoospores or the production of other spore forms), or sexually. Sexual reproduction usually occurs at times of stress in the life cycle (i.e., at the end of the growing season or during unfavourable environmental conditions).

Britannica English vocabulary.      Английский словарь Британика.