Biochemical Tests: Lipids (OCR AS Biology)

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Alistair

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Alistair

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Biochemical Tests for Lipids

Identifying biological molecules

  • Different qualitative reagents can be used to identfy the presence of biological molecules in samples
    • Ethanol is used to identify lipids
    • Biuret reagent is used to identify proteins
    • Benedicts solution and iodine are used to identify carbohydrates

  • Qualitative reagents simply determine whether or not a substance is present in a sample
  • The quantity or concentration of the substance present is not determined

Practical: the emulsion test for lipids

  • The emulsion test can be carried out quickly and easily in a lab to determine if a sample contains lipids
  • Lipids are nonpolar molecules that do not dissolve in water but will dissolve in organic solvents such as ethanol

Apparatus

  • Test tubes
  • Test tube rack
  • Ethanol
  • Pipettes
  • Food sample
  • Mortar and pestle (if food sample is solid)
  • Water
  • Gloves

Method

  • Add ethanol to the sample to be tested
  • Shake to mix
  • Add the mixture to a test tube of water

2.1 Emulsion test_2, downloadable AS & A Level Biology revision notes

The Emulsion test for lipids forms a milky colour

Results

  • If lipids are present, a milky emulsion will form (the solution appears ‘cloudy’); the more lipid present, the more obvious the milky colour of the solution
  • If no lipid is present, the solution remains clear

Limitations

  • This test is qualitative - it does not give a quantitative value as to how much lipid may be present in a sample

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Alistair

Author: Alistair

Expertise: Biology & Environmental Systems and Societies

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.