Gas exchange exam questions

• Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills. - 3 marks

  1. Water and blood flow in opposite directions;
  2. Blood always passing water with a higher oxygen concentration;
  3. Diffusion gradient maintained throughout length (of gill) OR Diffusion occurs throughout length of gill OR If water and blood flowed in same direction equilibrium would be reached;
• Explain two ways in which the structure of fish gills is adapted for efficient gas exchange. - 2 marks

  1. Many lamellae / filaments so large surface area;
  2. Thin (surface) so short diffusion pathway;
• Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange. - 3 marks

  1. Tracheoles have thin walls so short diffusion distance to cells;
  2. Highly branched / large number of tracheoles so short diffusion distance to cells;
  3. Highly branched / large number of tracheoles so large surface area (for gas exchange);
• Explain how one feature of an alveolus allows efficient gas exchange to occur. - 2 marks

  1. (The alveolar epithelium) is one cell thick;
  2. Creating a short diffusion pathway / reduces the diffusion distance
• Describe the pathway taken by an oxygen molecule from an alveolus to the blood. - 2 marks

  1. (Across) alveolar epithelium;
  2. Endothelium / epithelium of capillary;
• Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill. - 3 marks

  1. Water and blood flow in opposite directions;
  2. Maintains diffusion/concentration gradient of oxygen OR Oxygen concentration always higher (in water);
  3. (Diffusion) along length of lamellae/filament/gill/capillary; Accept: all/whole of lamellae/filament//gill/capillary
• Explain why death of alveolar epithelium cells reduces gas exchange in human lungs. - 3 marks

  1. Reduced surface area;
  2. Increased distance for diffusion;
  3. Reduced rate of gas exchange;
• Describe and explain the mechanism that causes lungs to fill with air. - 3 marks

  1. Diaphragm (muscle) contracts and external intercostal muscles contract;
  2. (Causes volume increase and) pressure decrease;
  3. Air moves down a pressure gradient Ignore along OR Air enters from higher atmospheric pressure;
• Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange. Do not refer to surface area or moisture in your answer - 2 marks

  1. Flattened cells OR Single layer of cells;
  2. Reduces diffusion distance/pathway
  3. Permeable;
  4. Allows diffusion of oxygen/carbon dioxide;
• Explain two ways in which the structure of fish gills is adapted for efficient gas exchange. - 2 marks

  1. Many lamellae / filaments so large surface area;
  2. Thin (surface) so short diffusion pathway;