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 -
- 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
