ORGANSIATION J

• Organelles —> cells —> tissues—> organs—> organ systems
• Tissues - a group of similar cells working together to perform common function
• Organs - a group of different tissues working together to perform a common function
• Enzymes - biological catalysts

  Enzymes are large proteins so made from a long chain of amino acids. 

  Enzymes have an active site with a unique shape that fits onto the substrate. The active site and substrate have to match ( lock and key model). In reality active site changes slightly (induced fit model) 
• Factors that effect enzymes 

  Temperature - higher temperature increases the rate of reaction. But if it gets too hot some of the bonds holding the enzyme together break. This changes the shape of the enzymes active site so the substrate will no longer fit. The enzyme is said to be denatured.  Enzyme shave an optimum temp where they work best.
• pH - If the pH is too low or too high it interferes with the bonds holding the enzyme together.  Enzymes optimum pH is often neutral 7 but not always eg pepsin optimum pH is 2 as it is in the stomach 
• Investigating effect of pH on enzyme activity


  1. Put a drop of iodine solution into every well in a spotting tile

  2. Place a bunsen burner on a heat proof mat and a tripod and gauze over the top. put a beaker of water on the top and heat water

  3. Add amylase solution to a test tube and a buffer solution with pH 5 to a test tube , put the tube into the beaker of water and wait 5 minutes

  4. Mix the test tubes together

  5. Every 30 seconds add some of the solution to each of the iodine wells

  6. Continue doing this until iodine solution remains browny orange and starch is no longer present

  7. Repeat the whole experiment with buffer solutions of different pH values to see how Ph effects the time taken for starch to be broken down
• If starch present

  blue black
• Independent variable

  • pH
• Dependent variable

  • Effect of pH on enzymes activity
• Control variable

  • Concentration and volume of amylase solution
• Enzymes and digestion

  Amylase breaks down starch into sugars : found in salivary glands , pancreas , small intestine 

  Protease breaks down protein into amino acids : found in stomach , pancreas , small intestine 

  Lipase breaks down lipids into fatty acids and glycerol : found in pancreas , small intestine 
• Bile is produced in the liver and is stored in the gall bladder before it is released into small intestine. 

  • neutralises acid from stomach which bile can do because it is alkaline 

  -it emulsifies fats . Break down fats into tiny droplets. This gives a much bigger surface area of fat for enzyme lipase to work on , which makes digestion faster. 
• Digestive system

  Digest and absorb foods
• Breakdown of food


  1. Chewing

  2. Amylase enzyme in saliva breaks down carbohydrates

  3. Goes down the gullet into the stomach
• Stomach

  1. Pummels the food with its muscular walls

  2. Produces the protease enzyme pepsin

  3. Produces hydrochloric acid that kills bacteria and gives the right pH for protease enzyme to work
• Pancreas

  • Produces protease, amylase and lipase enzymes
  • Releases these into small intestine
• Small intestine

  1. Produces protease, amylase and lipase enzymes to complete digestion

  2. Digested food is absorbed out of the digestive system into the blood
• Large intestine


  Absorbs excess water
• Rectum


  Where faeces is are stored
• Benedict's test - testing sugars : blue to brick red 

  1. Prepare food sample and transfer to test tube
  2. Prepare water bath to 75 degrees 
  3. Add some Benedictus solution to test tube 
  4. Place test tube in water bath for 5 mins 
  5. If food sample contains sugar it colour will change from blue to brick red
• Iodine solution - testing for starch : browny orange to blue black 

  1. Make food sample and transfer to test tube 
  2. Add a few drops of iodine and gently shake tube to mix contents. 

  3.  If sample contains starch the colour of the solution will change from orange to blue black 
• Biuret test - test for proteins : blue to purple 

  1. Prepare food sample and transfer to test tube 
  2. Add biuret solution to sample and mix contents of tube by gently shaking it
  3. If sample contains proteins solution will change fork blue to purple.
• Sudan 3 - test for lipids 

  1. Prepare food sample and transfer to test tube 
  2. Use pipette to add 3 drops of Sudan 3 solution to test tube and gently shake 
  3. Solution stains lipids. If the sample contains lipids the mixture will separate into 2 layers. The top layer will be bright red if lipids are present.
• Lungs and gas exchange 

  1. Air you breathe goes through trachea , this splits into two tubes called bronchi. One going to each lung. 
  2. The bronchi split into smaller tubes called bronchioles 
  3. Bronchioles finally end at small bags called alveoli where gas exchange takes place. 
• Alveoli carry out gas exchange in the body 

  Alveoli are surrounded by a network of blood capillaries.

  Blood passing next to the alveoli has just returned to the lungs so contains lots of carbon dioxide and very little oxygen. Oxygen diffuses out the alveolus and into the blood. Carbon dioxide diffused out the blood and into the alveolus to be breathed out. 

  When blood reaches body cells oxygen is released from the red blood cells and diffuses into body cells. At the same time carbon dioxide diffuses out of the body cells and into the blood. And is then carried back to the lungs.
• The heart is a double circulatory system 
• The right ventricle pumps deoxygenated blood to the lungs and take in oxygen. The blood then returns to the heart. 
• The left ventricle pumps oxygenated blood around all the other organs of the body. The blood gives up its oxygen at the body cells and the deoxygenated blood returns to the heart to be pumped out to the lungs again. 
• 1. Blood flows into the atria from the vena cava and the pulmonary vein .
  2. The atria contract pushing the blood into the ventricles 
  3. The ventricles contract forcing the blood into the pulmonary artery and the aorta and out of the heart 
  4. The blood then flows to the organs through arteries and is returned through veins 
  5. The atria fill again and the whole cycle continues 
• To keep things steady there are a group of cells in the right atrium which act as a pacemaker. And the pacemaker cells produce small electrical impulses which spread through surrounding muscle walls causing them to contract. 
• In some cases an artificial pace maker is needed to control heartbeat if the natural one doesn’t work. It is a little device implanted under the skin and has a wire going to the heart. It produces an electric current to keep the heart beating regularly.
• Blood vessels 

  Arteries - carry blood away from the heart 

  capillaries - involved in exchange of materials in tissues 

  Veins - carry blood to the heart 
• Arteries - carry blood under pressure 

  • heart pumps out blood at high pressures so the artery walls are strong and elastic 
  • The walls are thick compared to the size of the hole down the middle ( lumen )
  • They contains thick layers of muscle to make them strong and to allow them to stretch and spring back 
• capillaries - are really small 

  • arteries branch into capillaries 
  • They are only one cell thick 
  • They carry blood really close to every cell in the body to exchange substances with them 
  • They have permeable walls so substances can diffuse in and out 
  • The fact that they are one cell thick increases rate of diffusion 
• Veins - take blood back to the heart 

  • capillaries eventually join up to form veins 
  • Blood is at a lower pressure in the veins so the walls aren’t very thick 
  • They have a bigger lumen than arteries to help blood flow despite low pressure 
  • They have valves to help keep blood flowing in the wrong direction 
• Blood is composed of red blood cells , white blood cells and platelets all suspended within plasma 
• Red blood cells - carry oxygen from lungs to all cells in the body 

  • biconcave disc give stem a large surface area for absorbing oxygen 
  • They don’t have a nucleus so allows more room to carry oxygen 
  • Contain red pigment called haemoglobin 
  • In lungs haemoglobin binds to oxygen. 
• White blood cells - defend against infection 

  Some can change shape to engulf microorganisms int he process of phagocytosis 

  Produce antibodies to fight microorganisms 

  Produced antitoxins to neutralise any toxins produced by micro-organisms 

  Have a nucleus 
• Platelets - help the blood to clot 

  Prevents blood pouring out when we have a cut 

  Prevents things from entering our blood