Biology

• Tissues


  A group of similar cells that work together for a specific purpose
• Organs


  A group of different tissues that work together for a specific purpose
• Organelles


  • Sub-cellular structures
• Animal tissues


  • Muscular
  • Glandular
  • Epithelial
• Muscular tissue


  • Contracts/relaxes for movement
  • Produces chemicals (enzymes, hormones)
• Human organ systems


  • Nervous
  • Digestive
  • Excretory
  • Respiratory
  • Reproductive
  • Circulatory
• The gas exchange systems have organs adapted to be efficient exchange surfaces
• The stomach


  • Has muscular tissue to contract and churn up food
  • Has glandular tissue that produces enzymes to break down food
  • Has a folded lining to increase surface area
  • Has tough epithelial tissue to cover and protect
• Parts of the human digestive system

  • Mouth
  • Esophagus
  • Stomach
  • Liver
  • Gall bladder
  • Pancreas
  • Small intestine
  • Large intestine
  • Rectum
• Physical digestion


  Breaks down large chunks of food into smaller pieces by teeth grinding and stomach churning
• Chemical digestion


  Enzymes break down large insoluble molecules into smaller soluble ones
• For 6 mark questions on the digestive system, key points needed are: each part relies on that before, mouth breaks down food -> gullet -> stomach, small intestine relies on food being digested in stomach, pancreas produces enzymes, only waste goes to large intestine
• Catalyst


  Something that speeds up the rate of reactions without being used up
• Enzyme


  A large protein molecule that acts as a biological catalyst
• Active site


  An area in the structure of enzymes with a unique shape that binds to a specific substrate molecule
• Enzymes are made of protein
• How enzymes act


  1. Substrate molecule fits into active site like a lock and key

  2. Reaction takes place rapidly

  3. Products are released from active site

  4. Enzyme is then ready for another reaction
• Reactions catalysed by enzymes include: building large molecules from smaller ones, breaking down large insoluble molecules into smaller soluble ones, changing one molecule into another
• Importance of enzymes


  • Chemical reactions needed for life could not take place fast enough without enzymes to speed them up
  • Each reaction is controlled by a specific enzyme so many metabolic reactions can take place in the same small space without interfering with one another
  • Enzymes enable cells to have the control that makes it possible for cell chemistry to work
• Catalysts increase reaction rate without changing themselves chemically. Enzymes are proteins that are biological catalysts; their amino acid chains are folded to form the active site (matches the shape of the specific substrate molecule). They bind to the active site.
• Metabolism is the sum of all reactions in the body
• Functions of biological molecules

  • Lipids: insulation, energy storage
  • Proteins: cell growth, organelles
  • Carbohydrates: release/store energy
• Lipid


  Glycerol with three fatty acids
• Protein


  Made of different amino acids
• Carbohydrate


  Starch, simple sugars
• Catalysts catalyse chemical reactions. Enzymes are biological catalysts.
• Enzymes are made of proteins, with a specific 3D shape and active site.
• Enzymes are not used up in reactions.
• Enzyme-substrate complex


  When an enzyme and its substrate are bonded together
• The lock and key hypothesis describes that all substrates have a specific shape and will only bind to a complementary shaped enzyme.
• Enzymes are specific because they will only match up with a certain shaped substrate.
• At low temperatures, enzymes are inactive


  The optimum temperature is when the reaction works as fast as possible
• Enzymes denature (destroy) when they get too hot


  Denaturation changes the shape of the active site so the substrate no longer fits
• Up to the optimum temperature


  Enzyme and substrate molecules have more kinetic energy and there are more successful collisions between the substrate and enzyme's active site to form an enzyme-substrate complex
• Above the optimum temperature

  The enzyme molecule itself vibrates and the 3D shape of the active site changes so the substrate no longer fits, causing the enzyme to denature
• Digestive enzymes are made in glands, e.g. salivary glands, and also in the lining of the small intestine
• Mechanical digestion breaks down large chunks of food into smaller pieces
• Chemical digestion uses enzymes to break down large insoluble molecules into smaller soluble ones
• Human digestive enzymes work best at core body temperature of 37°C
• Different enzymes have different optimum pH levels