3.1.1

• unicellular organisms exchange substances through

  their cell membrane as it is their direct exchange surface
• unicellular organisms exchange through their cell membrane because

  they have a low respiration rate

  they have a large surface area : volume
• surface area : volume equation

  surface area / volume
• multicellular organisms exchange all substances through

  specialised exchange systems

  gas exchange surfaces with a large surface area

  transport systems to carry molecules
• multicellular organisms exchange through a specialised system because

  they have a high respiration rate

  they have a small surface area : volume
• some multicellular organisms can exchange through their

  body surface
• some multicellular organisms are able to exchange through their body surface due to

  thin, flat body shape meaning all body cells are close to the surface
• insects have what type of activity levels?

  high activity levels meaning they have a high oxygen demand
• how does the gas exchange system in insects work

  provides oxygen directly to the cells
• insects bodies are covered in

  an exoskeleton made of chitin
• spiracles

  openings in the insects exoskeleton allowing gas diffusion
• trachea in insects and adaptations

  large tubes reinforced by chitin - to stop them from collapsing
• tracheoles in insects

  small tubes originating from a single cell that has formed a hollow tube that extends between body cells
• tracheoles in insects adaptations

  narrow diameter and close to body cells - short diffusion distance

  large number - create large surface area for gas exchange allowing rapid rate of aerobic respiration
• tracheal fluid in insects function

  during extreme rates of respiration cells respire anaerobically releasing lactic acid lowering the cells water potential.

  The fluid moves into the cells reducing the volume of fluid in the tracheoles drawing air in allowing for a larger surface area for diffusion and increased aerobic respiration
• sphincter function

  uses muscles to close spiracles and reduce water loss
• mass gas transport in insects mechanism

  contract muscles in thorax and abdomen changing their volumes causing pressure changes in the tracheas and tracheoles pushing gasses in and out
• air sacs in insects

  during mass transport the changes in volume of the thorax and abdomen squeeze the air sacs causing air to move from the air sacs into the tracheoles.

  they are also used when spiracles are shut for water conservation
• bony fish

  have evolved a skeleton made of bones
• bony fish activity levels

  large and active organisms

  high oxygen requirement
• why fish need a specialised gas exchange system

  low surface area : volume

  scales do not allow for diffusion of gases

  get their oxygen from water
• movement of water through a fish for gas exchange

  1. water enter through mouth
  2. water passes over gills
  3. diffusion between water and gills occurs
  4. water passes out of opercula opening ( covered by operculum)
• gills location in fish

  in the opercula cavity that is covered by the operculum
• gill lamellae function

  where gas exchange takes place as water flows over the gills
• gill lamellae adaptations

  large surface area - more diffusion can occur

  short distances between walls of lamellae and bloodstream - short diffusion distances, faster rate of diffusion

  network of capillaries - more blood is processed and moved away faster maintaining steep oxygen concentration gradient
• counter - current exchange system

  water flow is opposite to blood flow direction and diffusion takes place across the length of the lamellae

  so a steep oxygen concentration gradient is maintained

  80% of oxygen from water diffuses into the blood
• why parallel flow doesn't work in fish

  the blood and water would have the same concentration of oxygen as they reach equilibrium which is inefficient
• process of maintaining water flow when still in fish

  1. opens mouth
  2. water flows into mouth / buccal cavity
  3. buccal cavity floor drops
  4. increased volume for water
  5. operculum shuts
  6. increased volume in opercula cavity
  7. decreased pressure in opercula cavity
  8. floor of buccal cavity lifts
  9. decreased volume for water
  10. water pressure increases in buccal cavity
  11. water flows over gills into opercula cavity
  12. mouth shuts
  13. operculum opens
  14. sides of opercula cavity squeeze decreasing volume
  15. water pressure increases
  16. water flows out of opercula opening
• why mammals require a specialised gas exchange system

  low surface area : volume

  maintain a constant body temperature

  high oxygen demand

  get oxygen from air
• where are the lungs located

  in chest cavity
• rib function

  to protect lungs
• nasal cavity function

  trap dust and pathogens from air, warm and moisten air before it goes to lungs
• trachea function

  connects nasal cavity to lungs
• trachea adaptations

  C shaped cartilage in walls - prevents collapsing during inhalation but allows allows food to pass through oesophagus unobstructed

  ciliated epithelia cells and goblet cells - filter air before it reaches the lungs
• ciliated epithelia cells

  have cilia extending from cell membranes that beat mucus to throat so it is swallowed and digested
• goblet cells


  secrete mucus that traps dust and pathogens
• bronchi function

  carry air from trachea to each lung
• bronchi structure

  cartilage

  ciliated epithelia

  goblet cells
• bronchiole function

  allow air to pass to deeper parts of lungs from bronchus
• bronchiole structure

  large ones have cartilage

  smooth muscle to control amount of air passing in