Gas exchange in fish

• Label this diagram

  A) operculum closed

  B) operculum cavity

  C) operculum open

  D) gill bar

  E) gill filaments

  
• Label this diagram

  A) deoxygenated blood

  B) oxygenated blood

  C) gill lamellae

  
• Fish have gills as a specialised gas exchange surface
• How are gills specialised for their function?

  -they are internal and so are protected from damage
• Why do fish need a specialised gas exchange surface?

  -they are large and have a small surface area to volume ratio

  -they are metabolically active and so have a high demand for oxygen, which diffusion can't meet

  -they are large so cells at the centre are a long way from the body surface
• Why do gills have a large surface area?

  -lots of gill filaments

  -each gill filament has lots of gill lamellae
• Why do gills have a short diffusion distance?

  -gill filaments and lamellae are squamous epithelium (flattened tissue)
• What does countercurrent flow do?

  Maintains the concentration gradient across the whole gas exchange surface/gill lamellae. As a result, more oxygen can diffuse out of the water
• What is the function of the operculum?

  -opens to let water with high levels of carbon dioxide out

  -closes to increase the pressure within the gill cavity during ventilation movements
• How are gills adapted for efficient gas exchange?

  -gill filaments are covered with many gill lamellae at right angles, which increases the surface area

  -gill lamellae are very thin and very close to the capillaries, providing a short diffusion path for oxygen and carbon dioxide

  -gill filaments have a rich blood supply containing haemoglobin, which has a high affinity for oxygen
• Describe how ventilation works in bony fish.?

  -mouth opens and operculum closes

  -buccal cavity floor lowers

  -buccal cavity volume increases and pressure decreases compared to outside

  -water rushes into the mouth down a pressure gradient

  -opercular cavity expands

  -buccal cavity floor raises

  -pressure inside buccal cavity is now higher than in the opercular cavity

  -water moves from buccal cavity over the gills into the opercular cavity

  -mouth closes and operculum opens

  -the sides of the opercular cavity move inwards, increasing pressure

  -water rushes out of the fish through the operculum
• Use a simple flow chart to describe how ventilation works in bony fish.?

  Mouth opens -> buccal cavity floor lowers -> volume increases, pressure decreases -> water flows into the mouth -> mouth closes -> buccal cavity floor raises -> volume decreases, pressure increases -> water is forced over the gills -> opercular cavity pressure increases -> operculum opens -> water is forced out
• What is cocurrent flow?

  -water and blood flows in the same direction over the gill plates

  -blood with low oxygen coming from the body is in contact with water with high oxygen coming from the mouth

  -oxygen diffuses into the blood until equilibrium is reached
• What is countercurrent flow?

  -blood and water flow in opposite directions across the gill plate

  -blood with high oxygen leaving the gills is in contact with water entering the gill from the buccal cavity, which has a higher oxygen content than the blood
• Describe how countercurrent flow works.?

  -blood entering the gill filament has low oxygen concentration

  -water flowing opposite to the blood has high oxygen concentration

  -the water has a higher oxygen concentration than the blood across the whole gill plate, so equilibrium is never reached

  -so the concentration gradient is maintained over the entire gill

  -this means diffusion occurs across the entire length of the gill, so more oxygen is absorbed