Red algae

Red algae are photosynthetic organisms in the phylum Rhodophyta, mostly multicellular and especially diverse in marine habitats. Their phycobilin pigments capture light and often give them a red appearance.

Phycobilin: A family of water-soluble pigments that absorb light and transfer energy to photosynthetic reaction centers. Phycoerythrin and phycocyanin give many red algae their color and broaden the light they can use.
Phycoerythrin: A red phycobilin pigment that absorbs green and blue-green light. It helps many red algae photosynthesize with light wavelengths that penetrate seawater.
Agar: A gel-forming mixture of polysaccharides extracted mainly from certain red algae. Agar is harvested from red algae and used in food, microbiology, and biotechnology.
Rhodophyta: The eukaryotic phylum comprising red algae. Red algae are the organisms classified within this phylum.
Coralline algae: Red algae that deposit calcium carbonate in their cell walls. Their mineralized forms build and stabilize habitats on reefs and rocky shores.
Chloroplast: A photosynthetic organelle in plants and algae that converts light energy into chemical energy. Red algae perform photosynthesis in chloroplasts descended from an ancient primary endosymbiosis.
Phycocyanin: A blue phycobilin pigment that absorbs orange and red wavelengths. Alongside phycoerythrin, it contributes to light harvesting in red-algal photosynthesis.
Carrageenan: A family of sulfated polysaccharides extracted from red algae and used as gelling or thickening agents. Red-algal cell walls supply carrageenan for foods, cosmetics, and other products.
Primary endosymbiosis: An evolutionary event in which a eukaryotic cell engulfed a cyanobacterium that became a photosynthetic organelle. Red-algal plastids trace their ancestry to this acquisition of a cyanobacterial ancestor.
Kelp: Large brown algae that form underwater forests in temperate coastal waters. Kelp forests are often confused with red-algal seaweed habitats but belong to a different algal lineage.

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