2.2.11

Testing for Biological Molecules

Test yourself

Testing for Carbohydrates, Lipids and Proteins

Reagents can help us test what food substances are present. The first step is to grind up the food and add distilled water to dissolve some of the food. You can then test for the food substances:

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Starch

  • Add iodine solution to test for starch.
  • It will turn blue-black if starch is present.
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Sugar

  • Add Benedict’s reagent and heat for about two minutes to test for sugar.
  • It will turn any of green, yellow or red if sugar is present.
  • The colour depends on the concentration.
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Proteins

  • Add Biuret solution to test for proteins.
  • It will turn mauve or purple if proteins are present.
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Lipids

  • To test for lipids, add Sudan III (a fat-soluble dye).
  • If lipids are present, a red-stained oil layer will float on the water surface.
  • The presence of lipids can also be tested by adding ethanol.
  • The solution is added to water and shaken. If the solution turns cloudy, lipids are present.

Jump to other topics

1Cell Biology

1.1What's in Cells?

1.2Cell Division

1.3Transport in Cells

2Organisation

2.1Principles of Organisation

2.2Enzymes

2.3Circulatory System

2.4Non-Communicable Diseases

2.5Plant Tissues, Organs & Systems

3Infection & Response

4Bioenergetics

5Homeostasis & Response

5.1Homeostasis

5.2The Human Nervous System

5.3Hormonal Coordination in Humans

5.4Plant Hormones

6Inheritance, Variation & Evolution

7Ecology

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