碳水化合物(carbohydrate)
即醣类。自然界存量最丰富和分布最广泛的有机物，包括糖、淀粉和纤维素。一般分成四类︰单醣（如葡萄糖、果糖）、双醣（如蔗糖、乳糖）、寡醣和多醣（大分子可由多达一万个单醣单位连接而成，包括纤维素、淀粉和肝醣）。绿色植物藉光合作用产生碳水化合物。在大多数动物中，碳水化合物提供可迅速使用的储存能量，并在组织中使葡萄糖发生氧化，增强代谢过程。许多碳水化合物（但绝不是所有的）具有Cn（H2O）n的通式，这表示碳（C）原子连接氢原子（－H）、氢基（－OH；参阅functional group）和羰基，这种组合、次序和几何排列导致大量的同分异构体，也就是具有相同分子式的物质却具有不同的结构和性质。
English version：
carbohydrate
Any member of a very abundant and widespread class of natural organic compounds that includes sugars, starch, and cellulose. They are commonly classified as monosaccharides (simple sugars, e.g., glucose, fructose), disaccharides (2-unit sugars, e.g., sucrose, lactose), oligosaccharides (3-10 or so sugars), and polysaccharides (large molecules with up to 10,000 monosaccharide units, including cellulose, starch, and glycogen). Green plants produce carbohydrates by photosynthesis. In most animals, carbohydrates are the quickly accessible reservoir of energy, and oxidation (see oxidation-reduction) of glucose in tissues supplies energy for metabolism. Many (but by no means all) carbohydrates have the general chemical formula Cn(H2O)n. The carbon c atoms are bonded to hydrogen atoms (&singlehorzbond;H), hydroxyl groups (&singlehorzbond;OH; see functional group), and carbonyl groups (&singlehorzbond;C&doublehorzbond;O), whose combinations, order, and geometrical arrangement lead to a large number of isomers with the same chemical formula but different properties. The class is further enlarged because each isomer has various derivatives: uronic acids, sugars with an oxidized group; sugar alcohols, sugars with a reduced group; glycosides, compounds of sugars with other hydroxyl-group-containing molecules, and amino sugars, sugars with an amino group (see amino acid).