AQA GCSE Biology Trilogy: Food Tests

The Chemistry of Food:

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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

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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

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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

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Food Tests:

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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

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Lipids:

• Ethanol test for lipids -
  • Colourless ethanol turns cloudy white in the presence of lipids

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Proteins:

• Biuret solution test for proteins -
  • Blue Biuret solution turns purple in the presence of proteins

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