ALGAE

Chlorophyll-bearing organisms occurring in both saltand freshwater; they have no flowers or seeds, but reproduce by unicellular spores. They range in size from single cells to giant kelp over 100 ft long, and include most kinds of seaweed. There are four kinds of algae: brown, red, green, and blue-green. Blue-green algae are said to be the earliest form of life to appear on earth. The photosynthetic activity of algae accounts for the fact that over two-thirds of the world total photosynthesis takes place in the oceans. Algae are harvested and used as food supplements (see carrageenan, agar), soil conditioners, animal feeds, and a source of iodine; they also contain numerous minerals, vitamins, proteins, lipids, and essential amino acids. Alginic acid is another important derivative. Blue-green algae are water contaminants and are toxic to fish and other aquatic life. Phosphorus compounds in detergent wastes stimulate the growth of algae to such an extent that overpopulation at the water surface prevents light from reaching many of the plants; these decompose, removing oxygen and releasing carbon dioxide, thus making the water unsuitable for fish. Algae are being used in treatment of sewage and plant effluent in a proprietary flocculation process.

Algae are the simplest of green plants and their study is termed algology or phycology. The population of algae varies from a few hundred to several millions per gram of soil. The main groups of algae are green algae, bluegreen algae, yellow-green algae and diatoms. Algae form the first step in the colonization of land by plants, adding organic material and vital trace elements necessary for the growth of higher plants.
Algae are predominantly aquatic photosynthetic organisms, which transform light energy into energy-rich organic compounds. In soil, algae do not receive light but get their energy by oxidation of other materials.
Formerly regarded as plants, algae are now classified as members of the kingdom Protista. Algae are a heterogeneous group of cryptogamic plants comprising thirteen large phyla and several smaller groups, which are yet to be studied fully.
Algae are unicellular or multicellular (filamentous, ribbon-like or plate-like). The most familiar types are slimy, fibrous masses that grow in stagnant water. They tolerate a wide range of moisture conditions.
Some algae grow symbiotically with fungi, and are called lichens. Lichens are crucial to the early accumulation of organic matter on exposed rocks and parent materials forming the soil. Some blue-green algae fix atmospheric nitrogen and maintain nitrogen levels in soils used for paddy production.
Substances like copper sulphate are toxic to algae and serve as algicide. Organisms living on algae are called algicolous. Green algae, added to water cultures, seem to improve the growth of tobacco roots and their immunity to fungal infections.
Though algae have their own distinct morphological, cytological and reproductive properties, the basic biochemical mechanisms are very similar to other plants; all possess chlorophyll and carry out photosynthesis. Their nutrient requirements, carbohydrates, proteins and end product assimilation process are very similar to those of higher plants.
The temporary rapid growth of algae in fresh water is known as algal boom.