Algae is a latin word (Algae - Sea weeds). They are chlorophyll bearing, simple and primitive plants. These plants are autotrophs. Algae belongs to thallophyta and the plant body of algae is called thallus. i.e. the plant body is not differentiated into root, stem and leaf.
Most of the algae are living in aquatic region. It may be fresh water or marine water. Very few algae can survive in wet soil. Some algae are very minute and float on the surface of the water. These algae are called phytoplankton. Some of the algae are symbionts (Algae living with fungi and they both are mutually benefitted) . E.g. Lichen. A few species of algae are epiphytes. The branch of study of algae is called phycology or algalogy. Algae reproduces by three methods. They are:
* Vegetative reproduction takes place by fragmentation. E.g. Spirogyra.
* Asexual reproduction takes place by spore formation. E.g. Chlamydomonos.
* Sexual reproduction takes place by means of fusion of gametes. E.g. Spirogyra, Chara.
Algae are classified into different classes based on the pigments. They are given in Table 17.1.
Algae are consumed as food by people in Japan, England and also in India. E.g. Ulva, Spirulina, Chlorella etc. Some algae are used as food for domestic animals. E.g. Laminaria, Ascophyllum.
Some of the blue green algae are essential for the fixing of atmospheric nitrogen into the soil, which increases the fertility of the soil. E.g. Nostoc, Anabaena.
Agar agar is extracted from some red algae, namely Gelidium and Gracillaria. It is used to prepare growth medium in laboratories.
Iodine is obtained from brown algae like Laminaria.
Chlorella pyrenoidosa is used in space travel to get rid of CO2 and to decompose human wastes.
Single Cell Protein (SCP)
Some of the single cell algae and blue green algae are used to produce protein. E.g. Chlorella, Spirulina.