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Edexcel IAL·Biology·IAL Biology

Biological Molecules

14 min read

Carbohydrates, lipids, proteins and water — their structures, bonds and the chemical tests for each.

Living things are built from a handful of molecule families, each with a structure suited to its role.

Carbohydrates

Made of monosaccharides (e.g. glucose) joined by glycosidic bonds in condensation reactions. Two monosaccharides → a disaccharide (e.g. maltose); many → polysaccharides:

  • Starch (plants) and glycogen (animals) — compact energy stores.
  • Cellulose — straight chains giving strong plant cell walls.

Test: Benedict's solution with a reducing sugar turns from blue to brick-red on heating; iodine turns blue-black with starch.

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