food and diet

• seven food groups = carbohydrates, vitamins, fibre, water, lipids, protein, minerals
• balanced diet = when we have the correct amount of each of the seven food groups on a daily basis
• carbohydrates (bread, rice, pasta, potatoes) - used to release energy inside all body cells
• proteins (meat, fish, eggs, beans) - building (growth) and repairing cells
• lipids (butter, hard cheese, chocolate) - used for energy storage, insulation and protection
• fibre (fruit, vegetables and whole grains) - prevent constipation
• minerals (fruit, vegetables and red meat) - prevents deficiency disease (iron needed to make red blood cells. calcium strengthens bones)
• vitamins (fruit and vegetables) - prevents deficiency diseases

  vitamin c- healthy blood vessels

  vitamin d- for absorbing calcium
• water (all foods except dried, large amounts in fruits and vegetables) - for chemical reactions, as a solvent and for transport
• the molecules in carbohydrates = sugar and starch
• when we ingest starch in food that we eat, the starch is digested into a sugar called glucose
• glucose is known as a simple carbohydrate - it is a small molecule. it is represented as a hexagon shape, 1 hexagon = 1 glucose molecule. the individual glucose units can then be built into larger molecules. they connect with each other to form long chains, often with branches. these are complex carbohydrates which are used for storage e.g starch
• we need carbohydrates in our diet because they provide us with energy. glucose can be used immediately in the reaction of respiration to give us energy
• colour change of iodine when starch is present = yellow brown to blue black
• method for iodine test for starch

  1. using the spatula place a small amount of the food sample into 1 dimple on the tile
  2. add a few drops of iodine onto the food sample using the dropper in the lid
  3. observe any colour change you see in the results table
• benedicts test colour changes

  blue = no glucose

  green = some glucose ( a little)

  orange = some glucose (medium amount)

  brick red = lots of glucose
• method for benedicts test for glucose

  1. use a spatula to place a small amount of the food to test into the bottom of the test tube
  2. using the pipette add 2cm³ of benedicts solution into the test tube
  3. heat in the water bath and wait for a colour change from blue to brick red
  4. wait for apparatus to cool
  5. record results in results table
• we need protein for growth and repair. animal sources of protein = meat, fish, eggs

  plant sources of protein = peas, beans, lentils
• we need lipids in small amounts for insulation protection and storage of energy
• lipids should only be eaten in small amounts or we will develop obesity and heart disease
• emulsion test for lipids

  1. add 2cm³ of ethanol to a small amount of the food sample and shake carefully to dissolve the food. this is test tube 1
  2. take another test tube and add 2cm³ of tap water to it- this is test tube 2
  3. pour test tube 1 into test tube 2 as shown in the diagram
  4. if lipid is present, the clear solution will turn white (milk like) this is called an emulsion
• lipid present = white emulsion