Biology 4

• Balanced diet


  Contains the right amount of dietary sources to meet the daily requirements of the body
• Dietary resources


  • Carbohydrate
  • Fats
  • Water
  • Fibre
  • Mineral ions
  • Vitamins
  • Proteins
• Functions of organs of digestive system

  • functions of the organs of the digestive system

  
• Physical digestion


  The mechanical breakdown of food into smaller pieces without any chemical change to the food molecules
• Chemical digestion


  The breaking down of the large molecules in food into small soluble molecules that can be absorbed. This involves chemical reactions catalysed by digestive enzymes
• DIGESTION IN MOUTH


  1. Physical Digestion

  2. Chemical Digestion

  
• Physical digestion in mouth

  Breakdown of food into smaller pieces without change to the food
• Physical digestion in mouth


  • Increase surface area of food for enzyme action
  • Teeth (chewing & grinding)
  • Chewing breaks up the food and mucus softens the food
  • Food is rolled into bolus and passed down the oesophagus

  
• Chemical digestion in mouth

  The breaking down of the large molecules in food into small soluble molecules that can be absorbed. This involves chemical reactions catalysed by digestive enzymes
• Salivary Amylase


  Breaks down Starch into Maltose
• DIGESTION IN STOMACH


  1. Oesophagus

  2. Stomach

  
• Oesophagus


  • Muscular tube
  • Food moves through muscular contraction called peristalsis

  
• Physical digestion in stomach

  • Peristalsis in the stomach wall breaks up the food, and also mixes the food with gastric juice
• Chemical digestion in stomach

  • Gastric juice secreted by gastric gland
  • Gastric juice contains hydrochloric acid & pepsin
  • Hydrochloric acid stops the action of salivary amylase, provides an acidic medium for pepsin to work, and kills harmful microorganisms in food
  • Pepsin breaks down protein into polypeptide
• DIGESTION IN SMALL INTESTINE

  1. Small Intestine

  2. Bile

  3. Pancreatic juice

  
• Physical digestion in small intestine

  • Bile released into duodenum by gallbladder
  • Bile is alkali - neutralises the acid from stomach
  • Bile emulsifies fats = breaks fats into small pieces (increases the surface area)

  
• Chemical digestion in small intestine

  • Pancreatic juice contains amylase (starch to maltose), trypsin (protein to polypeptide), and lipase (fat to fatty acids and glycerol)
  • Epithelial cells of small intestine produce maltase (maltose to glucose) and lipase (fat to fatty acids and glycerol)

  
• Digestion of different foods

  • Amylase (salivary/pancreatic) - Starch to maltose
  • Maltase - Maltose to glucose
  • Pepsin - Protein to polypeptide
  • Trypsin - Protein to polypeptide
  • Bile - Break down big fats into small droplets
  • Lipase (pancreatic/epithelial) - Fats to fatty acids and glycerol

  
• Absorption in small intestine

  • Inner surface has numerous minute finger-like projections called villi, which increase the surface area for absorption
• Assimilation


  Uptake and use of nutrients by cells, takes place in the liver
• Absorption in large intestine

  • The colon absorbs water and mineral ions into the bloodstream
• Egestion


  The removal of undigested food from the body as faeces