from powerpoint

• Digestion


  The breakdown of large, complex, insoluble, molecules into simple, soluble ones that can pass through cell membranes
• Principles of digestion


  • Ingestion
  • Digestion
  • Absorption
  • Egestion
• Types of nutrition


  • Size of organism
  • Habitat
  • Diet
• Types of ingestion


  • Herbivores
  • Carnivores
  • Omnivores
  • Detritivores
  • Decomposers
  • Parasites
• Herbivores


  Feed on green plants and therefore have a diet high in carbohydrates
• Carnivores


  Feed on other animals and therefore their diet is high in protein
• Omnivores


  Feed on a varied diet of plants and animals and therefore have a diet consisting of carbohydrate and proteins
• Detritivores


  Consume dead organic matter (detritus) via their mouth, then digest it into simpler substances which are excreted out of their anus. Digestion is internal.
• Detritivores


  • earthworms, millipedes and blow fly larvae and slaters
• Decomposers


  Bacteria and fungi release enzymes outside of their cells to break down dead and decaying matter into simpler substances that they then absorb
• Parasites


  Organism that feed on the organic compounds present in the body of another living organism
• Enzymes


  • Large molecules need to be broken down chemically by ENZYMES
  • Enzymes are biological catalysts. They speed up chemical reactions in the body
  • Digestive enzymes speed up the breaking down process by holding the large particle (substrate) in place
  • The enzyme fits over the substrate perfectly – like a key fits a lock
• Main types of digestive enzymes


  • Amylase
  • Protease
  • Lipase
• Starch digestion


  1. Starch broken down into glucose

  2. Glucose moves into SI via facilitated diffusion

  3. Glucose moves from SI villi into blood stream via facilitated diffusion

  4. Glucose in blood stream

  5. Facilitated diffusion

  6. Respiration

  7. Respiration
• Mouth


  • Teeth are needed to tear, rip and chew food to physically break it into smaller pieces
  • Saliva makes the food moist and easy for swallowing
  • Amylase enzyme (in saliva) chemically breaks the carbohydrate starch down into maltose (disaccharide)
• Teeth types


  • Incisors = 2
  • Canine= 1
  • Premolars=2
  • Molars=3
• Saliva functions


  • Adds amylase to food to digest starch breaking them into sugars
  • Adds mucin to lubricate food for easier swallowing
  • Adds Antacids to neutralize acid to prevent tooth decay
  • Add anti-bacterial chemicals to kill bacteria that enter mouth with food
• Epiglottis


  Flap of cartilage that closes trachea (windpipe) when swallowing to prevent choking
• Oesophagus


  • Muscular tube that takes food from the throat and pushes it down through the neck, and into the stomach
  • Moves food by waves of muscle contraction called peristalsis
• Peristalsis


  Rhythmic waves of contraction of smooth muscles in walls of digestive tract
• Stomach


  • Stomach muscles contract and relax to mechanically break down the food
  • Mixes the food up with gastric juice and hydrochloric acid
  • Acid kills bacteria in the food
  • Gastric juice contains the protease enzyme PEPSIN to digest protein into amino acids
  • Food spends about 3-4 hours in the stomach
• Stomach functions


  • Food storage
  • Mechanical digestion - churns the food into semi solid mass called CHYME
  • Chemical digestion - Proteases break down proteins into amino acids
  • Disinfect food - HCl kills bacteria
• Stomach protection


  Mucus secreted by stomach cells protects stomach lining
• Duodenum


  • First section of small intestines (25cm)
  • Acid food from stomach mixes with digestive juices from pancreas, liver and intestines
• Duodenum digestive juices


  • Pancreatic juice (Pancreatic Lipase, Pancreatic Protease, Pancreatic Amylase)
  • Intestinal juice (Intestinal Lipase, Intestinal Protease, Intestinal Amylase)
  • Bile from liver
• Duodenum function


  Neutralizes acidic chyme from stomach and continues digestion
• Small intestine enzymes


  • Maltase (breaks maltose into glucose)
  • Protease (breaks peptides into amino acids)
  • Lipase (breaks lipids into fatty acids and glycerol)
• Absorption in small intestine

  • Digested food is absorbed through the wall of the small intestine into the blood stream
  • Small intestine has a large surface area to increase absorption - it is over 6 metres long, has bends, villi and microvilli
• Absorption through villi


  Glucose and amino acids pass into the blood capillary, fatty acids and glycerol move into the lacteal to be transported via the lymph system
• Large intestine


  Colon function is to absorb water (about 90%) from alimentary canal
• Egestion


  Indigestible food (e.g. fibre) passes into the large intestine (colon), water is absorbed back into the body, and the remaining solid waste called faeces is stored in the rectum and removed through the anus