B2 - Investigate energy content of food

• Food Tests 


  Can be used to identify the food types present in food
• Starch Test

  • Food type - starch
  • Method - add iodine solution
  • Result - if present, iodine turns from yellow-brown to blue-black
• Benedict‘s Test

  • Food type - sugar
  • Method - add Benedict’s solution and heat in a water bath
  • Results - if present, the solution changes from blue to a brick-red precipitate
• Biuret Test

  • Food type - protein (amino acids)
  • Method - add sodium hydroxide, then a few drops of copper sulfate and shake
  • Result - if present, the solution turns from blue to purple/lilac
• Ethanol Test

  • Food type - fat
  • Method - Shake the fat with ethanol then add equal amount of water
  • Result - if present, the colourless ethanol changes to a cloudy white emulsion
• Biological molecules 


  Carbohydrates, protein and fats are very important biological molecules. Each of them contains the elements carbon, hydrogen and oxygen, and protein also contains nitrogen
• Carbohydrates - simple 


  Simple carbohydrates are sugars such as glucose. They are simple because they are made up with one or two basic sugar units. Good sources of energy. Glucose is used in respiration. Lactose is sugar and energy source in milk. Sugars are fast release energy stores which means they can be quickly metabolised to release energy.

  
• Complex carbohydrates 


  Include starch, glycogen and cellulose. They are made up of many glucose units linked together. Starch and glycogen are very important storage molecules. Starch is the main storage molecule in plants and glycogen is an important storage molecule in animals. Cellulose is a structural carbohydrate, providing support in plant cell walls

  
• Protein 


  Proteins are long chains of amino acids bonded together. As there are 20 different types of amino acid, there are many different arrangements in which the amino acids can be linked together. Proteins can be structural or functional.

  
• Fats 


  The basic sub unit of fat consists of one molecule of glycerol and three fatty acid molecules. Fats are high in energy so are excellent storage molecules. Oils such as olive and rapeseed are fats. also known as lipids

  
• Practical apparatus

  • test tube
  • thermometer
  • g clamp and stand
  • mounted needle or forceps
  • heat proof mat
• Practical equation 


  Energy released in joules = mass of water (g) x rise in temp x 4.2
• To ensure results are valid

  • Use the same amount of each food
  • hold the burning food the same distance from the boiling tube
• Some (heat) energy will be

  • Lost to the air
  • Lost to heat the glass
  • Left in the burned food remains
• Image of practical 


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