Introduction to Algae

Algae are kept in division Thallophyta along with fungi. They differ from fungi in the presence of chlorophyll pigment and mode of their nutrition.

General characteristics of algae

• Algae are of universal occurrence. They are found in the variety of habitats like some member of algae grow in fresh water. Some are grown in marine water, on moist soil, on moist rocks, on snow, within or in animal or plant bodies.

1. Epizoic- algae grow on the outer surface of the animal body.
2. Endozoic- algae grow in the inner part of the animal body.
3. Epiphytic- algae grow in the plant body.
4. Endophytic- algae grow inside the plant body.

• Gametophytic plant body of algae is thallus which may be branched or unbranched
• Some members of algae are unicellular. Eg; Chlamydomonas. Some are multicellular. eg; macrocystis
• Each of the cells is bounded by the cellulosic cell wall. It is further differentiated into the outer mucilaginous sheath and inner cellulosic layer. Mucilaginoussheath makes plants body slippery to touch and protect from dead and decaying of the plant body.
• Reproduction takes place by vegetative, asexual and sexual methods. Vegetative multiplication by fragmentation, fission and tumor formation. Asexually reproduce by spore formation and common asexual spores are zoospores, autospore, aplanospore etc. Sexually reproduce by isogamy, anisogamy, and oogamy.
• Embryo stage is absent in algae.

Process involved in sexual reproduction

Sexual reproduction takes place by isogamy, anisogamy, and oogamy.

Isogamy

The fusion process of morphologically similar but physiologically dissimilar gametes is called isogamy. Male having the positive strain and female having negative strain are involved. Due to the opposite strains, they come close to each other and fuse together to form a diploid zygote. This process is also called conjugation.

Anisogamy

The fusion process of morphologically as well as physiologically different gametes is called anisogamy. The male is smaller and motile and female is larger and non-motile. Such types of gametes are called anisogamete and fusion process is called anisogamy or anisogamous sexual reproduction.

Oogamy

The fusion process of male gamete antherozoid and female gamete ovum or egg is called oogamy. Male gametes are developed in antheridium and female gametes are developed in archegonium. If the antherozoid and egg are developed in a separative reproductive sex organ fertilized product is zygote called oogamous type of sexual reproduction.

Classification of algae

On the basis of dominant photosynthetic pigment, storage food material, and cell wall component division algae are divided into three classes;

• Chlorophyceae(Green algae)
• Phaeophyceae(Brown algae)
• Rhodophyceae(Red algae)

Molecular formula of;

• Chlorophyll-a - C₅₅H₇₀O₅N₄ mg
• Chlorophyll-b- C₅₅H₇₀O₆N₄ mg
• Carotene- C₄₀H₅₆
• Xanthophyll- C₄₀H₅₆O₂

Economic importance of Algae

• Seaweeds such as Laminaria japonica and religiosa are used for the treatment of goiter as they contain iodine.
• Gelidium (as agar) is used in medicine as a laxative and in a culture medium for the growth of bacteria and for the manufacture of pills and ointments.
• Extracts of some algae like Digenea, Codium, alsidium, and Durvillea are effective vermifuge.
• Corallina cure worm infections and its extracts are used for the treatment of kidney, bladder and lungs diseases.
• Chlorella culturing tanks are kept during space journey because of their rapid oxygen liberating capacity so that cosmonauts could breathe clean air.