biochemical tests for molecules

• what's the biuret test for

  proteins
• biuret test

  1. The test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution.
  2. Then you add some copper(Il) sulfate solution.
• results for buret test

  If protein is present, the solution turns purple. If there's no protein, the solution will stay blue
• what does iodine test for

  starch
• Iodine test

  Just add iodine dissolved in potassium iodide solution to the test sample. If starch is present, the sample changes from browny-orange to a dark, blue-black colour. If there is no starch, it stays browny-orange.
• what does the emulsion test for

  lipids
• emulsion test

  • shake the test substance with ethanol for about a minute, then pour the solution into water.
  • If lipid is present, the solution will turn milky.
  • The more lipid there is, the more noticeable the milky colour will be.
  • If there's no lipid, the solution will stay clear.
• what does the Benedict's test for 


  sugars
• Benedict's test for reducing sugars

  • You add Benedict's reagent (which is blue) to a sample and heat it in a water bath that's been brought to the boil.
  • If the test's positive it will form a coloured precipitate - solid particles suspended in the solution. The colour of the precipitate changes
• Benedict's test for non-reducing sugars

  • If the result of the reducing sugars test is negative, there could still be a non-reducing sugar present.
  • add dilute hydrochloric acid and carefully heating it in a water bath that's been brought to the boil.
  • You then neutralise it with sodium hydrogencarbonate.
  • carry out the Benedict's test as you would for a reducing sugar
• colorimeter 


  a device that measures the strength of a coloured solution by seeing how much light passes through it
• biosensor 


  is a device that uses a biological molecule, such as an enzyme to detect a chemical. The biological molecule produces a signal (e.g. a chemical signal), which is converted to an electrical signal by a transducer (another part of the biosensor). The electrical signal is then processed and can be used to work out other information.