Algae are microscopic photosynthetic plants. They are among the simplest plant forms, having neither roots, stems, nor leaves. Algae typically range from single-cell entities (which impart a green color to surface waters) to branched forms that can be seen by the naked eye. The latter often appear as attached green slime on surface bodies of water. Diatoms refers to singlecelled algae which are housed in silica shells. The blue-green algae generally associated with water pollution are Anacystis, Anabaena, and Aphanizomellon. Green algae are Oocystis and Pediastrum. Algae are autotrophic; that is, they use carbon dioxide or bicarbonates as sources of carbon. Inorganic nutrients of phosphate and nitrogen as ammonia or nitrate are also used. Some trace nutrients are also necessary (magnesium, boron, cobalt, calcium). The reaction or process by which algae propagate is known as photosynthesis.The products of photosynthesis are new plant growth and oxygen. The energy supplied to the reaction is derived from sunlight. Pigments biochemically convert solar energy into useful energy for plant reproduction and survival. In prolonged absence of sunlight, plant matter performs a dark reaction to exist. In this case, algae absorb oxygen and degrade stored food to produce yield energy for respiratory functions. The reaction rate for the dark reaction is much slower than photosynthesis. Macrophytes are aquatic photosynthetic plants (excluding algae). They often appear on surface bodies of water as floating, submerged, and immersed aggregates. Floating plants are not anchored or rooted. In the animal kingdom, one of the simplest forms is the protozoan. Protozoa are single-celled aquatic animals that have relatively complex digestive systems. They use solid organic material as food and multiply by binary fission. They are aerobic organisms and digest bacteria and algae and, consequently, play an essential role in the aquatic food chain. The smallest type are the flagellated protozoa which range in size from 10 n to 50 These have long hairlike strands which provide motility by a whiplike action. The amoeba is a member of the protozoa family. Rotifiers are simple, multicelled, aerobic animals. These metabolize solid food. Rotifiers are found in natural waters, stabilization ponds, and extended aeration basins in municipal treatment plants. Crustaceans are multicellular animals (about 2 mm in size). They are herbivores which ingest algae and are in turn eaten by fish.
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