Virtual Adviser What are Algae?

Algae are a diverse group of primarily aquatic, mostly plantlike organisms that occur in such dissimilar forms as microscopic single cells, loose, filmy conglomerations, matted or branched colonies, or giant seaweed with root - like structures resembling stems and leaves. Most of the algae have characteristics in common with plants, in that they have cell walls, contain the green pigment CHLOROPHYLL, and manufacture their own food through the process of PHOTOSYNTHESIS. The chlorophyll may be masked by other pigments, giving the various types of algae predominantly different colors. Some types, more animal - like, are mobile (capable of moving about) and ingest organic food, although they may also contain chlorophyll and conduct photosynthesis. Soft, even gelatinous cell surfaces are usual, but some types form shells or scales, and others produce stony, coral - like, or calcareous, deposits.

Algae are worldwide in distribution, thriving in all bodies of water, rocky coastlines, and terrestrial environments with ample moisture. Some species are adapted to such extremes of temperature as hot springs or arctic snows. Others survive in sandy soils or deserts. The habitats of marine and coastal algae vary according to degree of wave action, height of tides, and the light intensity required for photosynthesis; the various algal types are found in distinct zones or layers in the oceans and on beaches and cliffs.

Algae are differentiated mainly by cell structure, composition of pigment, nature of the food reserve, and the presence, quantity, and structure of flagella. The following phyla, or divisions, are recognized:

Members of the BLUE - GREEN ALGAE, Cyanophyta, offer classification difficulties and are placed by some biologists among the bacteria. They are somewhat larger than most bacteria but resemble them in structure and most functions. Unlike true algae they are procaryotes, or one - celled organisms, unlike bacteria, however, no Cyanophyta exhibit sexual reproduction; nor do any have flagella, although a few forms are mobile by unknown means. Cyanophyta also have chlorophyll a, which no photosynthetic bacterium possesses, and they produce gaseous oxygen as a waste product just as do all other algae but no bacterium.

Fossil masses of simple cells about 3.5 million years old, called STROMATOLITES, which strongly resemble Cyanophyta, are of great significance in having most probably been the major or original contributors to the formation of the oxygen blanket that made possible the evolution of higher life forms. Some Cyanophyta are able to fix atmospheric nitrogen, which is of great ecological importance. Others are thermophiles ("heat - lovers") that represent a large percentage of the life found in hot or boiling springs or pools.

The Euglenophyta are free - swimming one-celled organisms of a worm - like shape; they lack cell walls and usually have one or two flagella and a red, light - sensitive eye - spot. Most species are green but contain other pigments besides chlorophyll. Some subsist both by photosynthesis and by ingesting other organisms. Because of their ambiguous form, they have been claimed as animals by some zoologists and as plants by some botanists.

The phylum Pyrrophyta, commonly called dinoflagellates, are one - celled free - swimming biflagellates abundant in tropical waters. They contain chlorophyll, carotene, and a large proportion of a golden - brown xanthophyll. Many have a cellulose wall arranged in two interlocking plates; a few resemble AMOEBA and ingest organic food. Dinoflagellates are second in importance to diatoms as providers of oxygen and as a base in the food chain. Many generate light when disturbed and glow at night in tropical seas.

Rhodophyta, the red algae, are multicellular branching filamentous seaweed, abundant in warm coastal waters. Their color is primarily derived from the pigment phycoerythrin, which enables them to utilize light for photosynthesis at much deeper ocean levels than any other marine algae. Most have gelatinous cell walls. Some species concentrate lime from seawater; their secretions and skeletons contribute to the formation of coral reefs.

Chlorophyta The green algae variously occur as single cells, as scum or film, as filamentous branching, or matted colonies, or as multicellular marine forms with leaf - like fronds. They are diverse in habitat and are the most conspicuous algal type, forming in ponds and streams, on rocks and trees and almost any damp surfaces, including the hair and claws of certain animals and even the shells of turtles. They are also common in soils. The green algae, typically grass green in color, are characterized by their resemblance to the higher plants rather than to other algae in pigment content, in food storage , and in cell walls. This has suggested to scientists that the higher plants are directly descended from the Chlorophyta.

The brown algae, Phaeophyta, possess the brown pigment fucoxanthin that masks the green color of chlorophyll. All are multicellular seaweed with differentiated parts that may superficially resemble true plants. Familiar types are the giant kelps and the genus Sargassum, which forms dense mats of surface vegetation in the Sargasso Sea.

It has been estimated that the marine algae account for more than 90 percent of the world's photosynthetic activity, making them the most important source of oxygen. Algae are also the main source of food for other aquatic life. Seaweed are used as food by many coastal peoples and are ground into livestock meal. The gelatinous substances carrageenan and ALGIN are used widely to impart a smooth consistency to ice cream, puddings, processed cheeses, jams, light beers, and other food products. They are also used for finishing leathers. Algin is an ingredient in cosmetics, car polishes, paints, and insecticides. Agar, extracted from red seaweed, is widespread in the Orient as a delicacy and is a familiar laboratory medium for culturing microorganisms. Fertilizers, detergents, polishes, and insulating and soundproofing materials often contain diatomaceous earth, composed primarily of sedimentary shells of diatoms. Now being investigated is the use of green algae as food for humans and livestock. When grown under suitable conditions, certain types, provide a good source of protein, fats, and carbohydrates. Chlorella "farms" have been established on a small scale in various countries. In sewage treatment, green and blue - green algae are a source of oxygen for bacteria that decompose wastes.

Algae can also be harmful to both plants and animals. Parasitic algae are a cause of plant rust. A recurrent RED TIDE produces a potent nerve toxin that may kill millions of fish in temperate and subtropical waters. In lakes and ponds over-rich in nutrients, blanketing growths of green and blue - green algae may smother fish and plant life .

The phylum Chrysophyta contains diverse marine and freshwater algae that are free - living, one - celled, or occasionally filamentous. Many form shells composed of silica or lime. Most have one or two flagella. Chrysophyta are grouped mainly by color, ranging from yellowish - green through golden to golden - brown, depending on the proportion of chlorophyll to carotene and xanthophyll, yellow and brownish pigments. The best known are the biflagellate DIATOMS, the most abundant of the marine plankton. Sometimes called the "grass of the sea," they produce more oxygen than all green land plants combined. The diatom's walls are impregnated with silica and hence glass - like, often giving the cell a jewel - like appearance. When diatoms die, they sink and form deposits of diatomaceous earth, which is used in preparing such commercial products as water filters, detergents, fertilizers, insulating and soundproofing materials, polishes, and paint removers. Much petroleum is also of diatom origin. The diatom cell wall consists of two overlapping halves. Most diatoms are autotrophic. That is, they produce their organic nutrients from inorganic materials through photosynthesis. Some are heterotrophic (obtaining organic nutrients from the environment) and storing food in fatty deposits within the cell. Most diatoms are sedentary, and only certain species, the so - called pennate diatoms, are capable of moving at all.