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