Organisation

• Levels of organisation in living organisms

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

  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli (air sacs where oxygen diffuses into blood)
• Double circulatory system


  • Right ventricle pumps blood to lungs for gas exchange
  • Left ventricle pumps blood around rest of body
• Heart rate control

  • Pacemaker cells in right atrium generate electrical impulses
  • Artificial pacemakers can control irregular heartbeats
• Blood

  • Red blood cells: bind to oxygen and transport it around the body
  • Plasma: transport blood cells and other substances around the body
  • Platelets: form blood clots
• Enzymes

  Large proteins that catalyse (speed up) reactions
• Enzymes are not changed in the reactions they catalyse
• Lock and key theory


  Simple model of how enzymes work
• Lock and key theory

  1. Enzyme's active site is a specific shape

  2. Enzyme will only catalyse a specific reaction because the substrate fits into its active site

  3. At the active site, enzymes can break molecules down or bind small molecules together

  4. When products released, enzyme's active site can accept another substrate molecule
• Digestive enzymes convert food into small, soluble molecules that can then be absorbed into the bloodstream
• Digestive enzymes

  • amylase
  • proteases
  • lipases
• As temperature increases

  The rate of reaction increases
• Optimum temperature is when the enzyme action works as fast as possible
• At extremes of pH or very high temperatures

  The shape of an enzyme's active site can change
• When the active site breaks down, an enzyme becomes denatured
• Denaturation


  The shape of the enzyme's active site is changed by heat or extreme pH
• The substrate can no longer bind to the active site, so the enzyme cannot catalyse the reaction - the enzyme has been denatured
• Active site

  Where the reaction occurs on the enzyme
• Substrate

  The molecule that fits into the enzyme's active site
• Amylase

  Enzyme that catalyses the breakdown of starch into maltose
• Catalyse

  To speed up a reaction
• Denatured

  When an enzyme's shape is changed so it can no longer function
• Enzyme

  A large protein that catalyses reactions
• Different enzymes have different optimum pH values
• In the stomach (acid environment)

  Protease enzymes work best
• In the small intestine (neutral environment)

  Amylase enzymes work best
• The lock and key mechanism is similar to what has been covered for joining two substrates together
• Leaves are organs because they contain many tissues that work together to perform photosynthesis
• Tissues in leaves

  • Waxy cuticle
  • Upper epidermis
  • Palisade mesophyll
  • Guard cells
  • Stomata
  • Spongy mesophyll
  • Lower epidermis
• Cuticle

  Waxy layer that makes the leaf waterproof
• Epidermis

  Single layer of cells that protects against water loss
• Palisade mesophyll


  Tightly packed cells with lots of chloroplasts to absorb light for photosynthesis
• Guard cells


  Control the opening and closing of the stomata
• Stomata


  Tiny openings on the lower surface of the leaf that allow gases to move in and out
• Spongy mesophyll


  Spherical cells with air spaces to allow gases to diffuse quickly and increase gas exchange
• Transpiration

  Water lost through the stomata by evaporation, pulling water up from the roots through the xylem
• Transpiration stream

  The constant movement of water up the plant
• Translocation


  The movement of dissolved sugars from the leaves to the rest of the plant through the phloem
• Specialised tissues


  • Xylem - one-way transport of water and minerals, made of dead cells with thick lignin-stiffened walls
  • Phloem - two-way transport of substances, living cells with end walls allowing flow
• Higher temperature


  Increases the rate of transpiration