Organisation

• Digestion in the mouth

  1. Food chewed

  2. Enzymes in saliva digest starch into smaller sugar molecules
• Digestion in the stomach

  1. Enzymes begin digestion of proteins

  2. Contains hydrochloric acid to help enzymes digest proteins

  3. Food spends several hours here

  4. Churning action of stomach muscles turns food into fluid to increase surface area for enzymes
• Digestion in the small intestine

  1. Pancreas releases enzymes (all 3) into small intestine

  2. Liver releases bile to speed up digestion of lipids and neutralize acid from stomach

  3. Walls of small intestine release enzymes to digest protein and lipids

  4. Small food molecules absorbed into bloodstream by diffusion or active transport
• Digestion in the large intestine

  1. Water absorbed into blood stream

  2. Feces released from body
• Products of digestion used by body to build new carbohydrate, lipids and proteins
• Some glucose used in respiration
• Enzymes

  Catalyse chemical reactions
• What are enzymes?

  • Large protein molecules
  • Have a groove on their surface- an active site
• How do enzymes work?


  1. Substrate attaches to active site

  2. Enzyme breaks down substrate into products
• Lock and key theory

  Enzymes are specific. Substrate must fit perfectly into active site
• Protease


  Enzyme that breaks down proteins into amino acids
• Where is protease found?

  • Found in: Stomach, pancreas, small intestine.
• When amino acids are absorbed by body cells, they join in a different order to make human proteins
• Amylase


  Enzyme that breaks down starch into simple sugars
• Where is amylase found?


  • Found in: Saliva, pancreas
• Lipase


  Enzyme that breaks down lipids into glycerol and 3 fatty acids
• Where is lipase found?

  • Found in: Pancreas, small intestine
• Where is bile?

  Made in liver and stored in gallbladder.
• Bile


  • Emulsifies lipids- converts large lipid droplets into smaller lipid droplets- increases surface area, increasing rate of lipid breakdown
  • Alkaline, creating alkaline conditions in small intestine, increasing rate of lipid digestion
• Enzyme optimum temperature


  As temperature increases, rate of reaction/enzyme activity increases. Enzyme and substrate moving faster, more collisions. Optimum temp for human body: 37C. Once temperature exceeds optimum temp, enzyme denatures.
• Enzyme Optimum pH

  pH where enzyme activity is maximum. Different for every enzyme. When pH becomes to acid/alkaline, enzyme denatures.
• Small intestine adaptations.


  • Long- provides large surface area for absorption of molecules
  • Villi- interior covered with millions of villi, which massively increase surface area
  • Microvilli found on surface of villi
  • Good blood supply- bloodstream rapidly removes products of digestion (increases concentration gradient)
  • Thin membrane- ensures short diffusion pathway
• Molecules which cannot be absorbed by diffusion are absorbed by active transport
• Humans have a double circulatory system


  • Blood passes through body twice
  • Can travel rapidly through body cells
  • Delivering oxygen cells need
• Heart

  • Organ consisting mainly of muscle tissue
  • Job is to pump blood around body
• Vena Cava

  Deoxygenated blood from body to heart
• Pulmonary artery

  Deoxygenated blood from heart to lungs
• Pulmonary vein

  Oxygenated blood from lungs to heart
• Aorta

  Oxygenated blood from heart to body
• Coronary arteries


  • Branch out of aorta and spread out into heart muscle
  • Provide oxygen to muscle cells of heart, which is used for respiration for energy for contraction
• Heart rate

  1. Pacemaker cells found in right atrium control natural resting heart rate

  2. Sometimes pacemaker stops working, can be replaced by implanting an artificial pacemaker- a small electrical device that corrects irregularities
• Path of blood flow through heart

  1. Blood enters atriums

  2. Atria contract, blood forced into ventricles

  3. Ventricles contract, blood forced out of heart
• Adaptations of heart

  • Valves prevent back flow
  • Left side of heart has thicker, muscular wall- right ventricle pumps blood into lungs but left ventricle pumps blood into body, needs greater force
• Arteries


  • Carry very high pressure blood from heart to body organs
  • Have thick muscular walls- allows them to withstand high pressure
  • Blood travels in arteries in surges every time heart beats (pulse)
  • Arteries have elastic fibres that stretch when blood passes through and recoil in between, to keep blood moving
• Capillaries


  • When blood passes through capillaries substances (eg. Glucose, oxygen) diffuse from blood to the cells
  • Carbon dioxide diffuses from cell back to blood
  • Very thin walls
  • Short diffusion pathway
  • Diffusion between blood and body cells rapidly
• Veins

  • Blood travelling slowly at low pressure- possibility of stopping or going backwards
  • Thin walls- low blood pressure
  • Contain valves- prevent backflow
• Components of the blood

  • Plasma
  • White blood cells
  • Red blood cells
  • Platelets
• Plasma


  • Liquid "part" of blood
  • Transports dissolved substances around body- soluble digestion products (eg. Glucose), carbon dioxide from organs to lungs, waste-product urea to kidneys to be excreted as urine
• White blood cells


  • Form part of immune system
  • Contain nucleus, contains DNA which encodes instructions that white blood cells need to do their job
• Red blood cells

  • Transport oxygen from lungs to body cells
  • Contain haemoglobin- combined with oxygen in lungs, forming oxyhaemoglobin. Oxyhemoglobin releases oxygen to organs
  • No nucleus- more room for haemoglobin
  • Bi-concave disk shape- greater surface area- oxygen diffuses in and out rapidly