Organisation

• Tissue


  A group of cells with a similar structure and function
• Organ


  A group of tissues working together for a specific function
• Organs are grouped into organ systems which work together to form organisms
• Main nutrients in food

  • Carbohydrates (starch)
  • Protein
  • Lipids (fats)
• Food molecules are too large to be absorbed into bloodstream so they have to be digested
• Digestion


  1. Large food molecules are broken down to small ones by enzymes

  2. Small molecules are then absorbed into bloodstream
• Parts of the digestive system

  • Mouth
  • Stomach
  • Small intestine
  • Large intestine
  • Faeces
• Enzymes


  Speed up reactions
• Enzymes


  • They are large protein molecules and they have a groove on their surface called the active site
  • Active site is where the substrate attaches to
  • Enzymes are specific, substrate must fit perfectly into the active site (the lock and key theory)
• Protein digestion


  1. Proteins are broken down by proteases

  2. Proteins are long chains of chemicals called amino acids
• Carbohydrate digestion


  1. Carbohydrates are broken down by carbohydrases

  2. Starch is broken down by amylase

  3. Amylase is found in saliva and pancreatic fluid

  4. Starch consists of a chain of glucose molecules

  5. When carbohydrates like starch are digested we produce simple sugars
• Lipid digestion


  1. Lipid consists of a molecule of glycerol attached to 3 molecules of fatty acids

  2. Digested by lipase which produces glycerol and fatty acids

  3. Lipase is found in pancreatic fluid and small intestine
• Bile


  • Made in the liver and stored in the gall bladder
  • Helps speed up digestion of lipids but it's not an enzyme
  • Emulsifies lipids
  • Alkaline so it can neutralise stomach acid
  • Increases rate of lipid digestion by lipase
• As temperature increases


  Activity of enzyme increases because more collisions per second
• Optimum temperature


  When the enzyme works at the fastest possible rate (Human optimum temperature is 37 degrees)
• If we increase temperature past optimum temperature


  Enzyme activity decreases to zero because enzyme molecule vibrates and the active site denatures
• Optimum pH

  Where enzyme activity is maximum
• If we make the pH more acidic or alkaline


  Enzyme activity drops to zero because active site denatures
• Protease enzyme in stomach


  Works best at acidic pH
• Enzyme released by pancreas (lipase)


  Works best at alkaline pH
• Food tests


  1. Grind food sample with distilled water

  2. Transfer paste to beaker and add more distilled water

  3. Stir so chemicals in food dissolve

  4. Filter solution to remove suspended food particles
• Testing for starch


  1. Place 2cm^3 of food solution into a test tube

  2. Add few drops of iodine solution (orange)

  3. If starch is present it turns blue-black if not, stays orange
• Testing for sugars


  1. Place 2cm^3 of food solution into test tube

  2. Add 10 drops of Benedict's solution (blue)

  3. Place test tube into a beaker and half fill beaker with hot water from kettle

  4. Leave for 5 mins

  5. If sugars are present changes colour. Green= small amount, yellow= more sugar, brick red= a lot of sugar
• Only works for reducing sugars like glucose
• Testing for proteins


  1. 2cm^3 food solution and 2cm^3 of biuret solution (blue)

  2. If protein is present the solution turns lilac or purple
• Testing for lipids


  1. Grind food with distilled water, don't filter solution

  2. 2cm^3 food solution add few drops of distilled water and ethanol

  3. Gently shake solution

  4. If lipids are present, white cloudy emulsion forms
• Effect of pH on amylase

  1. Place one drop of iodine solution into each well of a spotting tile

  2. 1st test tube add 2cm^3 of starch, 2nd test tube add 2cm^3 of amylase, 3rd test tube add 2cm^3 of pH 5 buffer solution

  3. Place all 3 test tubes into water bath at 30 degrees. Leave for 10 mins so solutions reach correct temperature

  4. Combine 3 solutions into one test tube and mix. Return to water bath and start stopwatch

  5. After 30 secs, transfer 1 drop of solution to the spotting tile

  6. Should turn blue-black

  7. Continue till remains orange

  8. Repeat with different pH buffers
• Problems: Only taking samples every 30 secs, looking for when it doesn't go blue-black which isn't always obvious
• Small intestine


  • The human small intestine is 5m. This provides a very large surface area for absorption of the products of digestion
  • Interior of small intestine is covered with millions of villi which massively increases surface area
  • Micro villi is on the surface which further increases the surface area
  • Villi have a very good blood supply so bloodstream rapidly removes the products of digestion this increases concentration gradient
  • Thin membrane ensures a short diffusion path
• Fish circulatory system


  Single circulatory system
• Human circulatory system


  Double circulatory system
• The heart


  • An organ consisting mainly of muscle tissue
  • Pump blood around body
  • 4 chambers - right atrium, left atrium, right ventricle, left ventricle
  • Separated by valves
• Blood flow through the heart

  1. Vena cava brings deoxygenated blood to the body

  2. Blood passes from heart to lungs in pulmonary artery

  3. Oxygenated blood passes from lungs to heart in pulmonary vein

  4. Oxygenated blood is pumped from heart to body in aorta
• Heart structure


  • Left side of heart has a thicker muscular wall than the right
  • Coronary arteries branch out of the aorta and spread out into heart muscle. Provide oxygen to muscle cells of the heart which is used in respiration to provide energy for contraction
  • Natural resting heart rate is controlled by pacemaker
• Arteries


  • Carry very high pressure blood from heart to organs
  • Thick muscular walls. Allows them to withstand very high pressure
  • Blood travels in surges every time heart beats. Elastic fibres that stretch and recoil
• Capillaries


  • When blood passes through capillaries, glucose and oxygen diffuse from blood to cells
  • Carbon dioxide diffuses from cells to blood
  • Thin walls so diffusion path is short. Allows substances to diffuse rapidly
• Veins


  • Blood travels back to heart through veins
  • Blood travels slowly at low pressure. This means it can stop and go backwards
  • Thin walls because blood pressure is low
  • Contains valves which stop back flow of blood
• Components of blood


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


  Transports soluble digestion products (glucose) from small intestine to organs, carbon dioxide from organs to lungs, and waste product urea from liver to kidneys
• Red blood cells


  • Transports oxygen from lungs to body cells
  • Contain oxygen-carrying molecule haemoglobin
  • No nucleus, which means they have more room for haemoglobin
  • Have dimples called biconcave discs which give greater surface area so oxygen diffuses out rapidly