gas exchange

• What happens to surface area to volume ratio as the size of organism increases?

  decreases
• What 3 factors affecting rate of diffusion are described by ficks law?

  - surface area

  - concentration gradient

  - length of diffusion pathway
• Why do spiracles need to close?

  to prevent water loss by evaporation
• What would trigger spiracles to open?

  - high internal concentration of carbon dioxide

  OR

  - low internal concentration of oxygen
• Where is the gas exchange surface in an insect? (where oxygen is delivered to cells)

  tracheoles
• How are insects tracheoles adapted for gas exchange?

  - highly branched with many end points to provide a large surface area

  - thin walls so a short diffusion pathway
• How does air enter and leave insects?

  through spiracles
• Why do mammals require a specialised respiratory system?

  - a large volume of oxygen is needed for a large number of cells to maintain the high levels of aerobic respiration

  - this high rate of respiration is required to provide the energy needed for high metabolic rates and to maintain a constant body temperature
• What is the function of a respiratory system?

  Provides a gas exchange surface between the air and the blood
• What are 2 adaptations of insects for gas exchange?

  - spiracles

  - tracheal system
• How does air move through the trachea?

  simple diffusion
• What allows oxygen to diffuse into cells?

  concentration gradient
• What role does a ventilation mechanism play in gas exchange?

  Maintains a steeper concentration gradient at the gas exchange surface for a faster rate of diffusion
• What is the gas exchange surface in fish?

  gill lamellae
• How are gills adapted for gas exchange?

  - gill filaments increase surface area

  - these are covered in lamellae which further increase surface area

  - lamellae walls are one cell thick to provide a short diffusion pathway
• Why is good flow important in gas exchange?

  maintains concentration gradient
• What is counter current mechanism in fish?

  - water and blood flow in opposite directions

  - means that there is always a concentration gradient along the whole length of the lamellae

  - if blood and water flowed in the same direction equilibrium would be reach
• Name the small tubes that carry gases directly to and from the cells of an insect

  tracheoles
• How does abdominal pumping increase the efficiency of gas exchange in insects?

  - lowers pressure

  - this establishes a pressure gradient

  - so that oxygen can move in

  - which establishes a concentration gradient
• How can you describe the direction of flow of blood and water in fish?

  counter current mechanism
• How are capillaries adapted for gas exchange?

  • walls are one cell thick made of endothelial cells which are also flattened
  • This provides a short diffusion pathway for a faster rate of diffusion
  • They are also narrow which slows down the speed of the blood, allowing more time for diffusion.
• How does the oxygen travel to respiring tissues in an insect?

  • Oxygen enters via the spiracles, diffuses through the trachea and many tracheoles and then diffuses directly into respiring cells
• How does the structure of a dicotyledonous leaf provide a large surface area?

  • Many air spaces and thin leaves
• How does the structure of a dicotyledonous leaf provide a short diffusion pathway?

  • Thin leaves and a close proximity between the gas exchange surface and the palisade mesophyll (where CO2 is used)
• How does the structure of a dicotyledonous leaf maintain a steep concentration gradient?

  • Carbon dioxide is immediately used in photosynthesis