Chapter 3

• Levels of organisation in living organisms

  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Organisms
• Cells


  Basic building blocks
• Tissues


  Groups of cells that have similar structures and functions
• Organs


  Groups of tissues working together to perform a specific function
• Organ systems


  Groups of organs working together
• Organisms


  Organ systems work together, forming an organism
• Enzymes are large proteins that catalyse (speed up) reactions
• Enzymes are not changed in the reactions they catalyse
• Lock and key theory

  1. The enzyme's active site (where the reaction occurs) is a specific shape

  2. The enzyme (the lock) will only catalyse a specific reaction because the substrate (the key) fits into its active site

  3. At the active site, enzymes can break molecules down into smaller ones or bind small molecules together to form larger ones

  4. When the products have been released, the enzyme's active site can accept another substrate molecule
• Parts of the digestive system

  • Mouth
  • Salivary glands
  • Oesophagus
  • Stomach
  • Liver
  • Gall bladder
  • Pancreas
  • Small intestine
  • Large intestine
  • Rectum
  • Anus
• Digestive enzymes


  Convert food into small, soluble molecules that can then be absorbed into the bloodstream
• Digestive enzymes


  • Amylase
  • Proteases
  • Lipases
• Amylase


  Breaks down starch into glucose
• Proteases


  Break down proteins into amino acids
• Lipases


  Break down lipids into fatty acids and glycerol
• The effect of pH on enzymes

  Different enzymes have different optimum pH values, allowing them to work well in environments with different pH values
• The effect of temperature on enzymes

  As temperature increases, the rate of reaction increases because enzyme and substrate molecules move around faster and collide more frequently, until the optimum temperature is reached, after which the enzyme becomes denatured and stops working
• Denaturation

  At extremes of pH or very high temperatures, the shape of an enzyme's active site can change, so the substrate can no longer bind to it and the enzyme cannot catalyse the reaction