section 2 - human nutrition

• Biological molecules


  • Nutrient
  • Composition
  • Chemical elements
  • Source
  • Function
• Carbohydrate


  • Glucose
  • Carbon, hydrogen and oxygen
  • Pasta
  • Provide energy
• Protein


  • Amino acids
  • Carbon, hydrogen, oxygen, sulfur and nitrogen
  • Meat
  • For growth and repair
• Lipid


  • 1 glycerol + 3 fatty acids
  • Carbon, hydrogen and oxygen
  • Butter
  • Provide energy
• Food tests


  • Nutrient
  • Reagent
  • Colour change if present
  • Extra
• Starch food test


  1. Take 5ml of sample and place in spotting tile

  2. Add 5 drops of iodine, shake

  3. If colour changes from brown/orange to blue/black, starch is present

  4. Repeat 3 times
• Glucose food test


  1. Take 5ml of sample and place in boiling tube

  2. Add 5 drops of benedicts, shake

  3. Place boiling tube in a water bath for 5 minutes

  4. Remove boiling tube from water bath

  5. If colour change from blue to brick red then glucose is present

  6. Repeat 3 times
• Protein food test


  1. Take 5ml of sample and place in boiling tube

  2. Add 5 drops of biuret, shake

  3. If colour change from blue to lilac then protein is present

  4. Repeat 3 times
• Lipid food test


  1. Take 5ml of sample and place in boiling tube

  2. Add 5ml of water and 5ml of ethanol, shake

  3. If colour change from transparent to cloudy lipid is present

  4. Repeat 3 times
• Balanced diet


  • Vitamin A
  • Vitamin C
  • Vitamin D
  • Calcium
  • Iron
  • Dietary fibre
• Vitamin A


  • Liver
  • Improve vision
• Vitamin C


  • Fruit
  • Prevent scurvy/healthy gums
• Vitamin D


  • Milk
  • Absorb calcium
• Calcium


  • Milk
  • Healthy bones and teeth
• Iron


  • Red meat
  • Makes haemoglobin
• Dietary fibre


  • Brown wholegrain pasta
  • Helps movement of food through the gut. Is not absorbed so is found in the faeces.
• Too little iron causes anaemia. Symptoms are tiredness and shortness of breath due to a lack of haemoglobin.
• Energy requirements


  Depend on activity level, age and gender
• Energy from food (P2) method

  1. Take a sample of food

  2. Measure 20ml of water using a measuring cylinder

  3. Place water in boiling tube in clamp on retort stand with a thermometer in it

  4. Record the temperature

  5. Measure and record the mass of the sample using the top pan balance

  6. Ignite the sample using the Bunsen burner

  7. Quickly move the food to below the boiling tube and over the heat proof mat

  8. Keep it there until it fully burns

  9. Record the temperature

  10. Repeat 3 times
• Safety precautions


  • Safety mat to collect burning sample
  • Boiling tube facing away from student so don't get burnt with steam
• Calorimeter


  Produces more accurate results because it is insulated so no heat is lost from the boiling tube to the environment, the burning sample is within the calorimeter so no heat is lost in the transfer, and there is a stirrer in the calorimeter spreading the rise of temperature evenly
• Enzymes


  • Amylase
  • Lipase
  • Protease
• Amylase


  • Substrate: Starch
  • Product: Glucose
  • Location: Mouth, Duodenum
• Lipase


  • Substrate: Lipid
  • Product: 1 glycerol + 3 fatty acids
  • Location: Duodenum
• Protease


  • Substrate: Protein
  • Product: Amino acids
  • Location: Stomach, Duodenum
• Enzyme optimum


  Enzymes have an optimum (they work best) temperature (37C) and pH. If they are overheated (55C) they become denatured (active site is irreversibly changed)
• Testing the effect of temperature on amylase

  1. Take 5ml of sample (starch)

  2. Add 5ml of amylase

  3. Add 5ml of benedicts

  4. Heat in a water bath for 5 minutes

  5. If colour changes from blue to brick red then glucose is present

  6. Repeat 3 times

  7. Repeat at different temperatures eg at 10, 30, 50C
• Digestive system structure and function


  • Mouth
  • Oesophagus
  • Stomach
  • Duodenum
  • Ileum
  • Colon
  • Rectum
  • Anus
• Mouth


  • Ingestion happens
  • Mechanical digestion- teeth breakdown food to increase surface area
  • Chemical digestion-saliva contains amylase
• Oesophagus


  Moves food down by peristalsis (circular muscle contractions)
• Stomach


  • Mechanical digestion-churning
  • Chemical-pepsin (protease)
  • Hydrochloric acid kills bacteria and makes the stomach stay at the optimum pH of pepsin (pH 2)
• Duodenum


  Chemical-contains protease, lipase and amylase
• Ileum


  Absorption of nutrients
• Colon


  Water is reabsorbed
• Rectum


  Faeces is stored
• Anus


  Egestion happens
• Liver


  • Bile is produced- bile emulsifies lipids to increase their surface area for lipase to break down lipids into 1 glycerol and 3 fatty acids
  • Bile neutralizes the acid from the stomach for optimum enzymes pH in the duodenum
• Pancreas


  Produces protease, amylase and lipase
• Gall bladder


  Stores bile
• Four processes of digestion


  • Ingestion (mouth)
  • Digestion (mouth, stomach, duodenum)
  • Absorption (ileum)
  • Egestion (anus)