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Microbiology => Agar => Red Algae
Red Algae
Red Algae, members of the phylum Rhodophyta, a large group of aquatic algae with approximately 6000 species. The red algae are characterized by reddish phycobilin pigments-phycoerythrin and phycocyanin-that mask the color of the chlorophylls. Most species grow near tropical and subtropical shores below the low-tide mark. A few are found in fresh water.
Most red algae are small to medium-sized multicellular organisms. The bodies of some are relatively complex, resembling those of kelp. Sexual structures and reproductive cells are highly specialized. Red algae vary greatly in shape; platelike, coralline, crustlike, leathery, and featherlike forms are known. Coralline species accumulate lime as they grow-appearing as flat pink coverings on stones, or fanlike growths resembling true coral-and contribute much of the lime in coral reef deposits. Fossils of red algae have been found in rocks 500 million years old.
Red algae are unique among the algae in that no flagellated cells are formed during the life cycle. Some species reproduce by vegetative fragmentation or spore formation, but most undergo a complex life cycle involving alternation of generations. Sexual plants (gametophytes) produce either male sex organs (antheridia or spermatangia) or female sex organs (carpogonia). The small male sex cells are carried by water currents to the elongated tip (the trichogyne) of a carpogonium, where fertilization occurs. The resulting zygote may divide directly but more commonly gives rise to numerous filaments. They produce spores that develop into an asexual plantlike growth, or sporophyte. The spores then develop into gametophytes.
Some red algae are of economic importance. Agar, which is used as a nutrient medium for growing bacteria and fungi and also in the food and drug industries, is obtained mostly from Gelidium and Gracilaria species. Carrageenin, obtained from Irish moss (Chondrus crispus), is used as a substitute for gelatin. Laver (Porphyra) is used as a food in Japan and the Philippines.
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