#red algae

• Agar — A natural gelling substance (polysaccharide) extracted from the cell wall of certain species of red algae (Rhodophyta), utilized as a solid culture medium in microbiology, a thickening agent in the food industry, and a stabilizer in chemistry; in a historical and religious sense, represented as a proper noun, it is the biblical name of Sarah's and Abraham's Egyptian maidservant, mother of Ishmael, considered an ancestral structural figure in Judaic, Christian, and Islamic traditions.
• Agar-agar — A mucilaginous polysaccharide product extracted from the cell wall of certain red marine algae (especially from the genera Gelidium and Gracilaria), commercialized as a powder, flakes, or gelatinous strips insoluble in cold water but soluble in hot water. Structurally, it gels upon cooling to form a rigid, thermally stable three-dimensional network, widely used in microbiology as a support for bacterial cultures, in confectionery as a plant-based substitute for animal gelatin (under code E406), and in pharmaceutical technology.