Algae are rich in carbohydrates, many inorganic and organic compounds, proteins, vitamins, etc. In some of the algae these substances are found in large amounts and are, therefore, used as food.
(1) The following members of Chlorophyceae (green algae) are used as food. Ulva (sea lettuce) is used as a vegetable
after drying and salting. Chlorella has a high percentage of proteins and lipids. Besides this, vitamins A and DD are also found in sufficient amounts. It has a very short life cycle and can be grown quickly. These characteristics make Chlorella a suitable food for future generations. It has also been grown easily in over-head tanks and was considered to be very suitable food for space flights.
(2) Members of Phaeophyceae (brown algae) used as food include Alaria, Laminaria, Sargassum, etc. The food value is due to proteins, fats and carbohydrates. They are rich in iodine and, therefore, goitre does not occur in the countries where these are eaten.
(3) Among Rhodophyceae (red algae) the genera commonly used as food are Chondrus (carrageen or Irish moss), Porphyra, Gigartina, Rhodymenia, etc. In species of Porphyra, vitamins C and B12 are found in sufficient quantities.
(4) A blue-green alga (Cyanophyceae) Nostoc commune is eaten as food in China, Java, etc. Another blue green alga, Spirulina is also used these days being very rich in proteins.
- Agar – Agar. These are obtained from members of Rhodophyceae, collectively called agarophytes e.g., Gelidium, Gracilaria, etc. Agar is a colloidal or jelly-like substance used for culturing bacteria and various other microorganisms. It is also useful in the preparation of medicines. Agar is also used in baking and confectionary
industry as emulsifying agent and in cosmetics, textile, leather and paper industries. It is also useful as a laxative.
- Carrageenin. It is a cell wall derivative of a red alga-Chondrus crispus and is used as an emulsifying and stabilizing agent in ice creams, chocolates, cosmetics, tooth pastes, etc.
- Algin. This cell wall derivative of some brown algae like Alaria, Ascophyllum, Fucus, etc., is widely used in preventing formation of crystals in ice-creams. It is also used in the rubber, tyre and paint industry. Besides, it is also used to stop bleeding and in the preparation of. soups, creams, sauces, etc.
- Diatomite. It is a deposit of dead frustule styles or cell walls of fossil diatoms (Bacillariophycean The walls of diatoms have a heavy deposit of silicon dioxide (SiO). When the diatoms, which form a major part of planktons, die, the remainder of the cell wall are deposited at the bottom of the water reservoirs. These deposits are called (or kieselguhr). It has diatomaceous earth following uses.
(1) It is used as an insulating agent in boilers, steam pipes, furnaces, etc., where the temperature rises to about 1000° F.
(2) It is used in car polishes, silver polishes and toothpastes.
(3) It is an absorbent for nitroglycerine, hence used in the transport of dynamite.
(4) Diatomite is also useful in oil refineries for the filtration process.
(5) It is useful in the preparation of paint, varnishes, abrasives, glass and porcelain.
Seaweeds are very rich in minerals and form the commercial source of their extraction. Kelps, the members of Laminariales of Phaeophyceae (Ascophyllum, Ecklonia, Laminaria, etc.) were the chief source of iodine extraction in Europe. Bromine is extracted from members of Rhodophyceae like Polysiphonia, Rhodymenia, etc.
In France, Iceland, Scotland and Norway, members of Phaeophyceae (brown algae) like Fucus Macrocystis, Sargassum, etc., are used as manure. Many useful inorganic minerals are obtained from them.
Blue-green algae (Cyanophyceae), viz., Aulosira, Anabaena, Nostoc, etc., fix elemental nitrogen and thus increase the soil fertility. These algae have special cells called heterocysts which are the sites for nitrogen fixation. P. K. De (1939) was the first to demonstrate N2 fixing ability of blue green algae. Fairly good yield of rice can be obtained over a number of years without addition of any nitrogenous fertilizer because of the presence of nitrogen fixing blue-green algae in the rice fields.
of north India could be Saline Usar reclaimed by growing blue green algae, like Nostoc, Anabaena, Seytonema, etc, The algae increase the mineral content of the soil and thus the crop yield.
Chlorella (green alga) yields antibiotiC an chlorellin which is useful against both gram positive and gram negative bacteria. Besides this, Laminaria, Ascophyllum, Rhododmela, etc., also have antibiotic properties.
Blue-green algae like Aulosira and Anabaena, and green algae like Chara and Nitella eliminate mosquito larvae from ponds and pools in which they grow.
Algae has always been useful for conducting physiological and genetic experiments since these can be easily grown and manipulated.
(1) Chlorella and Scenedesmus (green algae) have been extensively studying for photosynthesis.
(2) Acetabularia, a green alga, was used to establish the hereditary role of the nucleus.
(3) Halicystis, Valonia, etc., (green algae) are useful in the studies on permeability.
The sewage dispOsal is an aerobic process and production of oxygen from algal photosynthesis helps it. Algae like Chlorella, Scenede smus, Pediastrum, Oscillatoria, etc., can grow in these rich organic wastes and provide oxygen to aerobic bacteria. Hence, an oxidation pond is an example of algal bacterial symbiosis.