Biology – Testing for biological molecules | e-Consult
Testing for biological molecules (1 questions)
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Procedure:
- Add a small amount of the sample to a test tube.
- Add a few drops of iodine solution (typically potassium iodide dissolved in water) to the test tube.
- Mix the solution thoroughly.
Expected Results:
- Positive Result: The solution will turn a deep blue-black colour. This indicates the presence of starch.
- Negative Result: The solution will remain brown (the colour of the iodine solution itself). This indicates the absence of starch.
Chemical Basis: Starch is a polysaccharide composed of many glucose molecules linked together. Iodine (I2) molecules fit inside the amylose component of starch, forming a characteristic coloured complex. This complex absorbs light in the visible spectrum, resulting in the blue-black colour. If no starch is present, the iodine will not form this complex and the solution will remain brown.