Gas Exchange

• Name three features of an efficient gas exchange surface.

  1. Large surface area (e.g. cristae in mitochondria)
  2. Short diffusion pathway (e.g. capillary walls)
  3. Steep concentration gradient, maintained by a rich blood supply or ventilation (e.g. fresh air being brought into lungs)
• Why can't insects use their body surface as a gas exchange site?

  They have a waterproof chitin exoskeleton and a small SA:V (in order to preserve water).
• Name and describe the three main features of an insect's gas exchange system.

  1. Spiracles- holes on the body's surface that can be opened or closed by a valve for gas/water exchange.
  2. Tracheae- large tubes extending through all body tissue, supported by rings to prevent collapse.
  3. Tracheoles- smaller branches splitting of the tracheae.
• Explain the process of gas exchange in insects.

  1. Gas moves in and out of the tracheae through the spiracles.
  2. A diffusion gradient allows oxygen to diffuse into the body tissues while waste carbon dioxide diffuses out.
  3. Contraction of muscles in the tracheae allow mass movement of air in and out.
• Name the parts of the tracheal system in insects.

  A) Spiracle

  B) Tracheoles

  C) Body cells

  
• Why can't a fish use its body surface as a gas exchange site?

  They have a waterproof, impermeable membrane and a small surface area to volume ratio.
• Name and describe the two main features of a fish's gas exchange system.

  1. Gills- located within the body. Multiple gill filaments along their length.
  2. Lamellae- at right angles to gill filaments, give an increased surface area. Water and blood flow over them in opposite directions (countercurrent flow principle).
• Explain the process of gas exchange in a fish.

  1. The fish opens its mouth, by lowering the floor of the buccal cavity, to allow water to flow in, and then closes it again to increase pressure.
  2. The water passes over the lamella and oxygen diffuses into the bloodstream.
  3. Waste carbon dioxide diffuses into the water and flows back out of the gills.
• How does the countercurrent gas exchange system maximise oxygen absorbed by the fish?

  Maintains a steep concentration gradient as water is always next to blood with a lower oxygen concentration. This keeps the rate of diffusion constant across the entire length of the gill, enabling 80% of oxygen to be absorbed.
• Label the parts of a gill.

  A) Gill arch

  B) Filaments

  
• Name the parts of a gill filament.

  A) Oxygenated blood

  B) Flow of water

  C) Lamella

  
• Name and describe three adaptations of a leaf that allow efficient gas exchange.

  1. Thin and flat- short diffusion pathway and large SA:V.
  2. Stomata- pores on underside of leaf that allow gas in and out.
  3. Air spaces in mesophyll layer- allows gas to move around the leaf, facilitating photosynthesis.
• Name the parts of a leaf.

  A) Palisade mesophyll cell

  B) Spongy mesophyll cell

  C) Upper epidermis

  
• How do plants limit water loss while allowing gas exchange?

  • The stomata are regulated by guard cells which can open and close them.
  • Waxy cuticle
• Describe the trachea and its function in the mammalian gas exchange system.

  • Wide tube supported by C-shaped cartilage to keep the airway open during pressure changes.
  • Lined by ciliated epithelium cells which move mucus towards the throat to be swallow, preventing lung infections.
  • Carries air to the bronchi.
• Describe the bronchi and their function.

  • Supported by cartilage and lined by ciliated epithelium cells.
  • Narrow and there are two, one leading to each lung.
  • Allow passage of air to bronchioles.
• Describe the bronchioles and their function.

  • Narrower than bronchi.
  • Do not need to be kept open by cartilage, so have muscle and elastic fibres to allow them to contract and relax easily during ventilation.
  • Allow passage of air to the alveoli.
• Describe the alveoli and their function.

  • Mini air sacs lines with epithelium cells.
  • Site of gas exchange.
  • Walls are only one cell thick -> short diffusion pathway.
• Name the parts of the human gas exchange system.

  A) Diaphragm

  B) Intercostal muscles

  C) Alveoli

  
• Explain the process of inspiration.

  1. External intercostal muscles contract, while the internal ones relax. This pulls the ribcage up and out.
  2. Diaphragm contracts and flattens.
  3. Volume of thorax increases.
  4. Air pressure outside is higher than air pressure inside the lungs.
  5. Air is forced into the lungs.
• Explain the process of expiration.

  1. Internal intercostal muscles contract, while external ones relax. This brings the ribs down and in.
  2. The diaphragm relaxes and moves upwards.
  3. The volume of the thorax decreases.
  4. Pressure in the lungs increases.
  5. As the pressure in the lungs is higher than the pressure outside, the air is forced out.
• What is tidal volume?

  The volume of air we breathe in and out during each breath at rest.
• What is breathing rate?

  The number of breaths we take per minute.
• How do you calculate pulmonary ventilation rate?

  Tidal volume x breathing rate.

  These can be measured using a spirometer.