About Red Algae
Red algae comes under the class Rhodophyceae. They are the oldest group of eukaryotic algae. Members of the red algae family are multicellular and mostly inhabit marine environments, with a greater concentration in warmer areas, although a few species occur in freshwater. Red algae can be found in well-lit areas near the surface of the water, as well as at great depths in the ocean where relatively little light penetrates.
Red algae are distinguishable by their unique pigmentation, which comes from the presence of phycoerythrin, a red photosynthetic pigment. The red algae store energy reserves as a floridean starch, a polysaccharides which is very similar to glycogen. In addition to cellulose, red algae contain pectin, polysulphates, and polysaccharides in their cell walls. These are the source of agar and carrageens. Agar is a polysaccharide extracted from certain types of red algae.
It is commonly used as a food thickener and as a culture medium for growing microorganisms and propagating plants, such as orchids. Another polysaccharide derived from red algae is carrageenan, which acts as a food additive. It is often used to stabilize chocolate milk and to give a thick, creamy texture to ice cream and other soft processed foods. In addition to its culinary applications, carrageenan is also used to stabilize paints and cosmetics. They are non-flagellate and no motile cells is found at any stage of life cycle.
Red algae usually reproduce vegetatively through fragmentation.They reproduce asexually using non-motile spores and sexually through non-motile gametes. Sexual reproduction in this group of algae is that of the advanced oogamous type. The male gametes, known as spermatia, are formed individually in structures called spermatangium.
These male gametes are passively transported by water movements to the female gamete (the egg cell) located in the female reproductive structure, called the carpogonium, through a filament known as the trichogyne. They have unique post-fertilization developments which are found exclusive in this group of algae. The common members of red algae are: Polysiphonia, Porphyra, Gracilaria, Corallina and Gelidium.
