Section D

• Balanced diet


  Contains all the essential nutrients
• Components of a balanced diet


  • Carbohydrates
  • Proteins
  • Lipids
  • Minerals
  • Vitamins
  • Fibre
  • Water
• Different groups of people require different nutrients at different times of their lives
• The proportions of nutrients in a balanced diet vary depending on body size, stage of development and activity level
• Proteins


  Amino acids
• Lipids


  Fats, oils
• Fibre


  Cellulose, cell walls of plants
• Water


  Vital for all processes in living organisms
• Vitamin A


  Makes chemicals in the retina & protects surface of the eye
• Vitamin C


  Sticks together the cells that line surfaces in the body e.g. mouth
• Vitamin D


  Helps bones absorb calcium and phosphorus
• Calcium


  Component of bones and teeth
• Iron


  Component of haemoglobin in red blood cells
• Liver produces bile
• Oesophagus has peristalsis to move food
• Salivary glands produce saliva
• Large intestine absorbs water
• Rectum stores faeces
• Duodenum receives bile and pancreatic duct
• Gallbladder stores bile produced by the liver
• Energy content


  Energy given out by your food (J) / mass of your food (g)
• Digestive system


  • Ingestion
  • Digestion
  • Absorption
  • Egestion
• Alimentary canal


  • Continuous tube from mouth to anus
• Mechanical digestion


  Chewing, churning
• Chemical digestion


  Using enzymes to break down molecules
• Molecules need to be small and soluble to be absorbed
• Digestive enzymes


  Produced by cells, secreted into alimentary canal, speed up breakdown of large molecules
• Digestive enzymes


  • Carbohydrases (amylase, maltase)
  • Proteases
  • Lipases
• Digestion and absorption


  1. Mouth: carbohydrases

  2. Stomach: proteases

  3. Small intestine: proteases, carbohydrases, lipases
• Small intestine


  • Long, folded, villi, microvilli to increase surface area for absorption
• Villus


  One cell thick wall, capillaries, lacteals to absorb nutrients
• Bile


  Made in liver, stored in gallbladder, emulsifies fats, neutralises acid
• Calculating actual size from image size and magnification


  Actual size = Image size / Magnification
• duodeum - top part of the small intestine
• Ileum - rest of the small intestine
• Oesophagus peristalsis - moves food - waves of contraction down the gut
• Firbe - not digested, egested through anus
• Vitamins and mineral - not digested, absorbed into small intestine
• Water is absorbed back into blood, if not absorbed - diarhoea
• Iodine Test for Starch

  1. Put a few drops of starch solution in a well in the spotting tile

  2. Put a few drops of water into a second well as a control

  3. Add two drops of iodine solution to each well