Exchange surfaces

• Why do single cellular/ small organisms not require adaptations for gas exchange ?

  Simple diffusion is sufficient for them due to their large surface area to volume ratio and their short diffusion distance from cell membrane to cell centre
• Why do larger organisms require specialist gas exchange system ?

  higher metabolic rate

  smaller surface area to volume ratio

  larger diffusion distance
• Name 3 things that affect the rate of diffusion ?

  Surface area to volume ratio

  concentration gradient

  diffusion distance
• Name 3 adaptations of the trachea (mammals) and how their contribute to it's function ?

  C-shaped rings of cartilage, prevent collapsing

  Ciliated epithelium with goblet cells, prevent bacteria entering the lungs to prevent infection

  Smooth muscle, control the airflow
• Name a structural feature of the bronchi/bronchioles ?

  Cartilage to keep tubes open
• Which has more cartilage, bronchi or bronchioles ?

  Bronchi
• What is the purpose of the alveoli ?

  Site of mammalian gas exchange
• Name 3 adaptations of the alveoli that make it suited to its job ?

  Large capillary network to maintain a concentration gradient

  Walls made of squamous epithelial cells to provide a short diffusion distance

  Large number of alveoli in the lungs to increase surface area:volume
• What prevents the alveoli collapsing ?

  Surfactant
• Describe inhalation in humans ?

  External intercostals contract

  Diaphragm contracts

  Thorax cavity increases in volume
• Describe exhalation in humans ?

  External intercostals relax

  Diaphragm relaxes

  thorax cavity decreases in volume
• What is the difference between forced and normal exhalation ?

  In forced exhalation the internal intercostals contract too
• What can be measured by a spirometer ?

  Vital capacity

  VO max

  tidal volume

  residual volume

  breathing rate
• Vital capacity = maximum volume of air a human a inhale/exhale in 1 breath
• Tidal volume = volume of air inhaled/exhaled in a normal breath
• residual volume = volume of air that remains in the lungs
• What is the purpose of the residual volume ?


  To prevent the lungs collapsing
• Describe ventilation in fish ?

  1. Mouth opens and buccal floor lowers
  2. Operculum closes to expand the operculum cavity
  3. buccal floor rises
  4. water flows out of buccal cavity into operculum
  5. mouth closes and operculum opens
  6. water is forced over the gills and out of the fish
• What is the purpose of ventilation ?

  To maintain a constant concentration gradient
• Name the site of gas exchange in fish ?

  Gills
• What provides a large surface area in fish ?

  Multiple gill filaments, lined with rows gill lamellae
• What provides a fish with short diffusion distance ?

  Lamellae are single layer of flattened cells

  lined with capillary network
• How does a fish maintain a concentration gradient ?

  Counter current flow system
• Name 3 marking points for countercurrent flow ?

  Water flows in the opposite direction to blood in the capillaries

  oxygen rich water will always meet oxygen rich blood

  concentration gradient maintained across the entire Lamellae
• What are the 3 features of the tracheal system ?

  spiracles

  tracheae

  tracheoles
• Spiracles = small holes that run along the insects abdomin, they allow air flow in/out the insect
• Tracheae = lined with rings of chitin to prevent collapse
• Tracheoles = branch off from tracheae, filled with tracheal fluid, site of gas exchange
• What provides a large surface area in insects ?

  Many branching tracheoles
• What provides a short diffusion distance in insects ?

  thin walls of the tracheoles and they branch directly into the muscle fibres
• How is a concentration gradient maintained in insects ?

  Flapping of wings and contracting of abdomin provide constant air flow

  As respiration occurs the natural diffusion down the concentration gradient between CO2 and O2 in the muscles/tracheoles.
• How does the tracheal fluid increase gas exchage?

  During respiration, CO2 and lactic acid can be produced. These lower the water potential inside the muscle cells causing water to move via osmosis from the tracheole into the muscles. The volume water lost in the tracheole is replaced by air from the atmosphere.