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Algae exhibit cell walls composed of glycoproteins and polysaccharides, such as carrageenan and agar, distinct from those in land plants. Bacterial cell walls contain peptidoglycan, while archaeal cell walls vary in composition, potentially consisting of glycoprotein S-layers, pseudopeptidoglycan, or polysaccharides.
They have cellulose walls with alginic acid and also contain the polysaccharide fucoidan in the amorphous sections of their cell walls. A few species (of Padina) calcify with aragonite needles. [26] In addition to alginates, fucoidan and cellulose, the carbohydrate composition of brown algae consists of mannitol, laminarin and glucan. [52]
Red algal morphology is diverse ranging from unicellular forms to complex parenchymatous and non- parenchymatous thallus. [44] Red algae have double cell walls. [45] The outer layers contain the polysaccharides agarose and agaropectin that can be extracted from the cell walls as agar by boiling. [45] The internal walls are mostly cellulose. [45]
The structure of these algae is unicellular, and lacks flagella.Although most desmid species are unicellular, some genera form chains of cells, called filaments. A few genera form non-filamentous colonies, with individual cells connected by threads or remnants of parent cell walls.
Green tea-flavored yōkan, a popular Japanese red bean jelly made from agar A blood agar plate used to culture bacteria and diagnose infection. Agar (/ ˈ eɪ ɡ ɑːr / or / ˈ ɑː ɡ ər /), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from "ogonori" and "tengusa" (Gelidiaceae).
Green algae have chloroplasts that contain chlorophyll a and b, giving them a bright green colour, as well as the accessory pigments beta carotene (red-orange) and xanthophylls (yellow) in stacked thylakoids. [12] [13] The cell walls of green algae usually contain cellulose, and they store carbohydrate in the form of starch. [14]
[3] [4] Cellulose is an important structural component of the primary cell wall of green plants, many forms of algae and the oomycetes. Some species of bacteria secrete it to form biofilms. [5] Cellulose is the most abundant organic polymer on Earth. [6]
A frustule is the hard and porous cell wall or external layer of diatoms. The frustule is composed almost purely of silica , made from silicic acid , and is coated with a layer of organic substance, which was referred to in the early literature on diatoms as pectin , a fiber most commonly found in cell walls of plants .