Algae

Algae are a group of plantlike organisms that make their own food and live wherever there is water, light, and a supply of minerals. Like plants, algae contain chlorophyll, which means that they produce their own food by photosynthesis (using sunlight). There are thousands of different species of algae, ranging from microscopic diatoms to huge ribbons of seaweed. Since algae use the Sun's energy to make their own food, they eventually become food for other kinds of life, just as plants do. Classifying algae is difficult, and experts are constantly revising their ideas. Although algae resemble plants in many ways (they have cell walls and make their own food), some algae can move about and even absorb organic food like animals. However, most algae belong to the kingdom Protista and are considered to be the simplest form of plants (despite the fact that they have no roots, stems, or leaves).

Most algae are aquatic, meaning that they need water to survive, grow, and reproduce. Algae can be found almost anywhere there is water. One of the most common is often seen as the green on the surface of ponds or streams. Some algae merely float near the water's surface while others are capable of moving about on their own. Seaweed is a common form of algae that can be found in the ocean or on the seashore. Even the green, powdery film sometimes seen on trees or on old wooden fences is caused by an algae named Pleurococcus, which is unusual because it is one of the few algae that can survive away from water. Since all algae require light to make food, most are found near the water's surface, although photosynthesis can occur in extremely clear water at a depth of 100 meters (328.1 feet). Marine algae are very important to life on Earth since they produce about 90 percent of the oxygen that is created by the process of photosynthesis. Like green plants, algae take in the carbon dioxide that humans and animals exhale and release the oxygen that humans and animals need to breathe. Single-celled algae make up a large part of the phytoplankton of the oceans. Phytoplankton are found at the beginning of the food chain and form the basis of all nutrition in the sea. Even some whales feed on phytoplankton. Since all marine life is ultimately dependent on this first link in the food chain, there would be no fish to catch and eat without algae.

TYPES OF ALGAE

The different species of algae are grouped into phyla (related groups) according to their pigment (color) and the form in which they store food. Some are better known and easier to identify than others. The six main phyla of algae are diatoms, dinoflagellates, euglenas, green algae, red algae, and brown algae.

Diatoms. Diatoms make up the largest and most important part of phytoplankton and are also the easiest algae to identify (besides seaweed). Each one-celled diatom is protected by a tiny, two-part case that it makes out of silicon dioxide. When a single marine diatom dies, its hard case or shell drifts to the ocean bottom where over time, thick layers of these cases accumulate and are compressed to form a rock called diatomite. This valuable powdery rock is almost pure silica and is used commercially as an abrasive, filtering, or insulating material.

Dinoflagellates . Dinoflagellates almost always live in salt water and form the second most important part of phytoplankton after diatoms. These onecelled algae move about using whiplike tails called "flagella." As algae, dinoflagellates possess chlorophyll but they have red pigment rather than green. When the dinoflagellate population sometimes explodes for unknown reasons, it causes what is known as a "red tide." Red tides sometimes contain a nerve poison that can kill fish and people who eat infected fish.

Euglenas. Euglenas live in fresh water and are able to move with a long, whipping tail. Euglenas combine both plant and animal characteristics. Like plants they are able to produce their own food through photosynthesis. However, like animals, euglenas are also able to capture and eat food. Although they do not have a cell wall, they have a flexible layer inside their membrane as well as an "eyespot" that responds to light.

Green Algae. Green algae make up the phylum Chlorophyta and are distinguished by the presence of chlorophyll. They can be one-celled or many-celled and usually live in water, although they can survive in other environments (like the damp side of a tree trunk). Many species of green algae form colonies (a permanent group of related organisms) or grow in long chains, although some form a ball-shaped colony. Sea lettuce that grows in salt water is a good example of green algae.

Red Algae. Red algae are multicelled and get their name from their distinctive coloring. Since their unique red pigment allows them to absorb even the smallest amount of light, they are able to live far below the ocean surface and still make their own food by photosynthesis. Their food is a type of carbohydrate or starch called carrageenan, and it is used commercially to give toothpaste and even pudding its smooth creaminess.

Brown Algae. Brown algae are multicelled and most species live in salt water. Brown algae, also called kelp, grows into fields that are sometimes 100 yards (91.4 meters) long. Kelp or brown algae play an important role in the ocean as they provide both food for many fish and invertebrates (animals without a backbone) and a place to live and hide for many small fish. People in many parts of the world eat brown algae, and it is used commercially in ice cream, marshmallows, and fertilizer. Despite the fact that some kelp can grow as long as 100 feet (30.48 meters), they lack the complex structure of plants and are still considered algae.

ESSENTIAL TO LIFE ON EARTH

Algae play a key role in sustaining life on Earth since they give off oxygen and absorb much of the carbon dioxide that is produced by not only be humans and animals, but also the burning of fossil fuels. They also form the basis for most food chains in fresh water and ocean habitats

and have many valuable commercial purposes. For example, brown algae provide a natural source for the manufacture of chemicals called alginates that are used as thickening agents and stabilizers in the industrial preparation of foods and pharmaceutical drugs.

[See alsoFood Web/Food Chain ]