gas exchange

• 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.

  1. Flattened cells reduces diffusion distance/pathway;

  2. Permeable so allows diffusion of oxygen/carbon dioxide;
• Tidal volume is the volume of air inhaled and exhaled during a single breath when a person is resting. The tidal volume in a person with emphysema is reduced compared with the tidal volume in a healthy person.

  Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveoli.

  1. Less carbon dioxide exhaled

  2. So reduced diffusion/concentration gradient between blood and alveoli;

  3. Less movement of carbon dioxide out of blood
• Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system.

  1. Blood and water flow in opposite directions;

  2. Diffusion/concentration gradient maintained along length of lamella/filament;
• Describe and explain the mechanism that causes lungs to fill with air.

  1. Diaphragm muscle contracts and external intercostal muscles contract;

  2. Causes volume increase and pressure decrease;

  3. Air moves down a pressure gradient and enters from higher atmospheric pressure;
• Two solutions often used to stain tissues are haematoxylin solution and iodine solution.

  • Haematoxylin solution stains DNA a blue colour.

  • Iodine solution stains starch a blue-black colour.

  The scientist used haematoxylin solution and not iodine solution to stain the lung tissue.

  Suggest why

  1. This lung tissue does not contain starch;

  2. Makes nucleus visible;
• Particulate matter is solid particles and liquid particles suspended in air. Polluted air contains more particulate matter than clean air.

  A high concentration of particulate matter results in the death of some alveolar epithelium cells. If alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened tissue.

  Explain why death of alveolar epithelium cells reduces gas exchange in human lungs.

  1. Reduced surface area;

  2. Increased distance for diffusion;

  3. Reduced rate of gas exchange;
• Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill.

  1. Water and blood flow in opposite directions;

  2. Maintains diffusion/concentration gradient of oxygen as Oxygen concentration always higher in water

  3. Diffusion along length of lamellae
• Use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly

  1. Stomata close;

  2. Less carbon dioxide uptake for less photosynthesis
• Describe the pathway taken by an oxygen molecule from an alveolus to the blood.

  1. Across alveolar epithelium;

  2. Epithelium of capillary;
• Explain how one feature of an alveolus allows efficient gas exchange to occur.

  1. The alveolar epithelium is one cell thick;

  2. Which reduces the diffusion distance;
• Describe the gross structure of the human gas exchange system and how we breathe in and out.

  1. Air passes through the trachea, then the bronchi, then the bronchioles, then the alveoli for gas exchange;

  2. Breathing in - diaphragm contracts and external intercostal muscles contract;

  3. Causes volume increase and pressure decrease in thoracic cavity to below atmospheric, resulting in air moving in;

  4. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;

  5. Causes volume decrease and pressure increase in thoracic cavity to above atmospheric, resulting in air moving out;
• Explain ways in which an insect's tracheal system is adapted for efficient gas exchange

  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;

  4. Tracheae provide tubes full of air so fast diffusion into insect tissues;

  5. Fluid in the end of the tracheoles that moves out into tissues during exercise so faster diffusion through the air to the gas exchange surface;

  6. Body can be moved by muscles to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;
• The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water.

  Some other species of insect have larvae that are a similar size and shape to damselfly larvae and also live in water. These larvae do not actively hunt prey and do not have gills.

  Explain how the presence of gills adapts the damselfly to its way of life

  1. Damselfly larvae has higher metabolic / respiratory rate;

  2. So uses more oxygen
• Explain two ways in which the structure of fish gills is adapted for efficient gas exchange

  1. Many lamellae / filaments so large surface area;

  2. Thin surface so short diffusion pathway;
• Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills.

  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