Plants that live in water

One group of nonvascular plants is the many-celled algae. They live in water. Some of them are seaweeds. Like all other plants, many-celled algae have the green pigment called chlorophyll in their cells and can use sunlight to make their own food. Besides chlorophyll, some kinds of many-celled algae also have other pigment, in them. So, instead of looking green, some of these algae are divided into groups based on the kinds of pigments they contain.

None of the many-celled algae have roots, stems, or leaves. However, many large seaweeds have a long part that looks like a stem; this part is called a stripe. Some seaweeds also has a flat part that looks like a leaf. This part is called a blade. These parts are different from a true stem or a true leaf in that they do not have water-carrying or food-carrying tissues. Some kinds of algae also have a part called a holdfast. The holdfast fastens a plant to a shell or a rock in the water.

Among the different kinds of many-celled algae are the brown algae, the red algae, and a few green algae.

The largest kinds of brown algae, known as kelp, float on the ocean’s surface. They have stripes, blades, and balloon-like parts called air bladders. The air bladders help the plants float.

Most red algae grow on the ocean floor. Red algae have been found growing as far down as 200 meters below the water’s surface.

Some of the many-celled green algae float. Ulva or sea lettuce, is a kind of green algae that grows on the ocean floor.

Economic importance of algae

Algae use chlorophyll and sunlight to make food by means of photosynthesis.

Besides making food, algae also give off oxygen. Oxygen is a by-product of photosynthesis. Many animals depend on algae for both food and oxygen. Algae are important to animals for this reason. In fact, some people believe that if there were no algae (both one-celled and many-celled ones), there would not be enough food and oxygen for all the animals on the earth.

Some people depend on algae for food. In Japan, almost everyone eats a food known as nori. It comes from laver, a kind of red algae. The Japanese eat 130 000 tons of this seaweed each year. It is eaten in soups and biscuits. People in Korea, Ireland, Great Britain, and New Zealand also eat it.

Have you ever eaten algae? You might be surprised to find out that you have. In the many countries, algin is used to thicken foods such as ice-cream. Algin comes from brown algae. Some ingredients that may be found in food are gelose, agar, carrageenan, nori (red algae), kombu (brown algae).

Algae are important in other ways too. Some are used as fertilizers. Some are a source of iodine. Some are used to make certain drugs. Others can be used to make paints and soap.

Scientists who study bacteria use algae, too. They grow bacteria on jellylike agar. It comes from red algae.

Algae and products made from algae have a long history of usefulness. Dulse, a red alga, has been used as food for people and domestic animals for centuries. The algae now most widely used for food is nori, grown chiefly by coastal villagers in Japan. Nori is dried into sheets that are used in soups and biscuits and as a flavoring in many foods.

Although most algae are low in protein, they contain concentrated minerals and some starch. In many countries, dried algae are ground into a powder and added to animal feed as a mineral supplement. Algae yield valuable extracts. Agar, an extract taken from red algae, is a jellylike substance that is used for laboratory cultures in which bacteria are grown.

Carrageenin is another extract from red algae that is used to keep small particles in suspension in many foods. For example, carrageenin prevents chocolate from separating out in chocolate milk. Carrageenin is a common ingredient in jams and jellies, instant coffee, honey, wine and ice cream.