= Carbohydrate
{wiki}
<Carbohydrates> are a family of <chemical substances> encompassing <monosaccharides>, combinations of <monosaccharides>, and their derivatives. <Glucose> is a small <carbohydrate>; <cellulose> is a long-chain <polysaccharide>. <Deoxyribose> illustrates why composition alone does not define the family: replacing a <hydroxy group> in <ribose> by <hydrogen> still leaves a <carbohydrate>. See https://goldbook.iupac.org/terms/view/C00820[IUPAC Gold Book: carbohydrates].
Many familiar <monosaccharides> have a <molecular formula> of the form $\mathrm C_n\mathrm H_{2n}\mathrm O_n$, equivalently $\mathrm C_n(\mathrm H_2\mathrm O)_n$. This explains the historical name, “hydrate of <carbon>”, but does not mean the <molecule> consists of <carbon> mixed with intact <water> <molecules>. Nor is it a universal formula: <deoxyribose> has $\mathrm C_5\mathrm H_{10}\mathrm O_4$. The family is defined through chemical structure and relationships, not that ratio. See https://goldbook.iupac.org/terms/view/C00820[IUPAC's definition and origin of the name carbohydrate].
The useful surprise is the variety of roles obtainable from related building blocks. <Glucose> participates in <metabolism>, <ribose> forms part of <RNA>, and linked <glucose> units make structural <cellulose> in a plant <cell wall>. Understanding <carbohydrates> therefore connects cellular <energy>, molecular information, and material structure. See https://www.ncbi.nlm.nih.gov/books/NBK26883/[Alberts et al., Molecular Biology of the Cell: the chemical components of a cell].
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