Unit 2

• Biological molecules


  Things like carbohydrates, lipids and proteins. They're generally long, complex molecules made up from smaller basic units.
• Carbohydrate molecules contain the elements carbon, hydrogen and oxygen
• Starch and glycogen


  Large, complex carbohydrates, which are made up of many smaller units (e.g. glucose or maltose molecules) joined together in a long chain
• Proteins


  Made of long chains of amino acids. They all contain carbon, nitrogen, hydrogen and oxygen atoms.
• Lipids (fats and oils)


  Built from fatty acids and glycerol. Lipids contain carbon, hydrogen and oxygen atoms.
• Before a Food Test

  1. Get a piece of food and break it up using a pestle and mortar

  2. Transfer the ground up food to a beaker and add some distilled water

  3. Give the mixture a good stir with a glass rod to dissolve some of the food

  4. Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food
• Carbohydrates, proteins and lipids are made up from specific elements
• Benedict's test


  Used to test for glucose in foods
• Benedict's test


  1. Prepare a food sample and transfer 5 cm³ to a test tube

  2. Prepare a water bath so that it's set to 25 °C

  3. Add some Benedict's solution to the test tube (about 10 drops) using a pipette

  4. Place the test tube in the water bath using a test tube holder and leave it in there for 5 minutes

  5. If the food sample contains glucose, the solution in the test tube will change from its normal blue colour. It will become green or yellow in low concentrations of glucose, or brick-red in high concentrations of glucose.
• Iodine solution test


  Used to test for starch in foods
• Iodine solution test


  1. Make a food sample and transfer 5 cm³ of your sample to a test tube

  2. Then add a few drops of iodine solution and gently shake the tube to mix the contents

  3. If the sample contains starch, the colour of the solution will change from browny-orange to black or blue-black.
• Biuret test


  Used to test for proteins in foods
• Biuret test


  1. Prepare a sample of your food and transfer 2 cm³ of your sample to a test tube

  2. Add 2 cm³ of biuret solution to the sample and mix the contents of the tube by gently shaking it

  3. If the food sample contains protein, the solution will change from blue to pink or purple. If no protein is present, the solution will stay blue.
• Sudan III test


  Used to test for lipids in foods
• Sudan III test


  1. Prepare a sample of the food you're testing (but you don't need to filter it). Transfer about 5 cm³ into a test tube

  2. Use a pipette to add 3 drops of Sudan III stain solution to the test tube and gently shake the tube

  3. Sudan III stain solution stains lipids. If the sample contains lipids, the mixture will separate out into two layers. The top layer will be bright red. If no lipids are present, no separate red layer will form at the top of the liquid.
• Essential nutrients


  • Carbohydrates
  • Proteins
  • Lipids
  • Vitamins
  • Minerals
  • Water
  • Fibre
• Balanced diet


  Gives you all the essential nutrients you need - in the right proportions
• Factors affecting energy requirements

  • Activity level
  • Age
  • Pregnancy
• Calorimetry experiment


  1. Weigh a small amount of dry food and skewer it on a mounted needle

  2. Add a set volume of water to a boiling tube

  3. Measure the temperature of the water, then set fire to the food using a Bunsen burner flame

  4. Hold the burning food under the boiling tube until it goes out, then light it again and repeat until it won't catch fire anymore

  5. Measure the temperature of the water again
• Amylase


  Converts starch into maltose
• Maltase


  Converts maltose into glucose
• Proteases


  Convert proteins into amino acids
• Lipases


  Convert lipids into glycerol and fatty acids
• Parts of the alimentary canal

  • Mouth
  • Oesophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Rectum
• Bile


  • Neutralises stomach acid and emulsifies fats
• Peristalsis


  The squeezing action of the muscular tissue in the alimentary canal that moves food through the gut
• Villi in the small intestine

  • Increase the surface area for absorption of nutrients
  • Have a single permeable layer of surface cells and a good blood supply to assist quick absorption