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AQA GCSE Biology Trilogy: Food Tests

The Chemistry of Food:

Carbohydrates:

  • Consist of carbon, hydrogen and oxygen

  • Are made up of sugars, e.g. glucose -

    • single sugar

    • C6H12O6

  • Complex carbohydrates -

    • such as starch and cellulose

      • cellulose is used as support in plants

    • are long chains of simple single units

Lipids:

  • Consist of carbon, hydrogen and oxygen

  • Fats and oils

  • The most efficient energy store

  • Can be combined to create hormones and are used in the nervous system

  • Insoluble in water

  • Made up of 3 molecules of fatty acids chemically joined to 1 molecule of glycerol

    • The glycerol molecule always is the same

    • The fatty acids can vary

      • This determines whether the lipid is a solid or a liquid

Proteins:

  • Consist of carbon, hydrogen, oxygen and nitrogen

  • Used for building cells and tissues

  • Are the basis for enzymes

  • Act as muscles, tendons, insulin, antibodies, enzymes and catalysts

  • Make up around 15%-16% of the human body

  • Found in meat, fish, pulses and cheese

  • Long chains of amino acids

  • Bonds are sensitive to pH levels and temperature

Food Tests:

Carbohydrates:

  • Iodine test for starch -

    • Yellow / red iodine turns blue / black in the presence of starch

  • Benedict’s solution test for sugars -

    • Blue Benedict’s solution turns brick red when heated in the presence of sugars

Lipids:

  • Ethanol test for lipids -

    • Colourless ethanol turns cloudy white in the presence of lipids

Proteins:

  • Biuret solution test for proteins -

    • Blue Biuret solution turns purple in the presence of proteins

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AQA GCSE Biology Trilogy: Food Tests

The Chemistry of Food:

Carbohydrates:

  • Consist of carbon, hydrogen and oxygen

  • Are made up of sugars, e.g. glucose -

    • single sugar

    • C6H12O6

  • Complex carbohydrates -

    • such as starch and cellulose

      • cellulose is used as support in plants

    • are long chains of simple single units

Lipids:

  • Consist of carbon, hydrogen and oxygen

  • Fats and oils

  • The most efficient energy store

  • Can be combined to create hormones and are used in the nervous system

  • Insoluble in water

  • Made up of 3 molecules of fatty acids chemically joined to 1 molecule of glycerol

    • The glycerol molecule always is the same

    • The fatty acids can vary

      • This determines whether the lipid is a solid or a liquid

Proteins:

  • Consist of carbon, hydrogen, oxygen and nitrogen

  • Used for building cells and tissues

  • Are the basis for enzymes

  • Act as muscles, tendons, insulin, antibodies, enzymes and catalysts

  • Make up around 15%-16% of the human body

  • Found in meat, fish, pulses and cheese

  • Long chains of amino acids

  • Bonds are sensitive to pH levels and temperature

Food Tests:

Carbohydrates:

  • Iodine test for starch -

    • Yellow / red iodine turns blue / black in the presence of starch

  • Benedict’s solution test for sugars -

    • Blue Benedict’s solution turns brick red when heated in the presence of sugars

Lipids:

  • Ethanol test for lipids -

    • Colourless ethanol turns cloudy white in the presence of lipids

Proteins:

  • Biuret solution test for proteins -

    • Blue Biuret solution turns purple in the presence of proteins