Biology Unit 1 tests

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Biuret Test

  • Detects peptide bonds in proteins
  • Mix a sample with Sodium hydroxide soloution at room temperature
  • Add very dilute copper sulphate soloution
  • Colour change from blue to purple shows presence of peptide bonds and therefore the presence of a protein
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Reducing sugar test

  • All monosacchairdes and some disaccharides are reducing sugars
  • Get a sample of the sugar and HEAT GENTLY with Benedicts soloution
  • Colour change from Blue to Red
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Non-reducing sugar test

  • Most disachharides are Non-reducing sugars. They will not produce a colour change in the reducing sugar test
  • In order to detect a non-reducing sugar it needs to be broken down into monosaccarides by hydrolysis
  • Add the sample to Hydrcholric acid and heat gently for 5 mins - will hydrolise the diasscahride into monosacchardies
  • Add sodium hydrogencarbonate to neutralise the hydrocholric acid - Benedicts test will not work in acidic conditions
  • Re-do the reducing sugar test : mix the soloution with benedicts reagnt and heat gently
  • Once again if a reducing sugar is present it willl change the colour of the soloution from blue to red
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Test for startch

  • Add Iodine solotuion to the sample
  • Colour change from yellow-blue/black
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Emulsion Test

  • Used to detect the presence of lipids
  • Add 5cm of the sample to 5cm of ethanol and shake well - dissolves lipid in the sample
  • Then add 5cm of water and gently stir
  • A cloudy white precipitation indicates the presence of a lipid. If there was no lipid then there would be no precipitate.
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