Biology 9700 · AS & A Level · Testing for biological molecules

Testing for biological molecules — practice question

Which sequence of steps is the most suitable way to carry out the emulsion test for lipids?

  • AAdd $2\,\text{cm}^3$ of water to the sample. Pour the water into a test-tube containing $2\,\text{cm}^3$ of ethanol. Lipids are present if the mixture becomes cloudy.
  • BAdd $2\,\text{cm}^3$ of ethanol to the sample and shake. Pour the ethanol into a test-tube containing $2\,\text{cm}^3$ of water and boil. Lipids are present if the mixture becomes clear.
  • CAdd $2\,\text{cm}^3$ of water to the sample and shake. Pour the water into a test-tube containing $2\,\text{cm}^3$ of ethanol and boil. Lipids are present if the mixture becomes cloudy.
  • DAdd $2\,\text{cm}^3$ of ethanol to the sample and shake. Pour the ethanol into a test-tube containing $2\,\text{cm}^3$ of water and shake again. Lipids are present if the mixture becomes cloudy.

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