Iodine Solution - GCSE Biology Definition

Iodine solution is a chemical solution used in biology labs to test for the presence of starch in different substances. It is usually a mixture of iodine and potassium iodide dissolved in water. When added to a material containing starch, the iodine solution changes colour from yellow/brown to blue-black, making it an easy way to see if starch is present. This reaction happens because the iodine molecules fit into the spaces of the long starch molecules. Iodine solution is commonly used in experiments that help students understand how plants store energy as starch.