4.1 SA:V Ratio

• A good gas exchange surface has a large surface area relative to volume to increase surface are for gas exchange.
• A good gas exchange surface is very thin to reduce the diffusion distance, so that materials cross the surface rapidly.
• A good gas exchange surface is selectively permeable to allow selected materials to cross.
• A good gas exchange surface has movement of an environmental medium (e.g. air) to maintain a diffusion gradient.
• A good gas exchange surface has movement of an internal medium (e.g. blood) to maintain a diffusion gradient.
• Which animal, an elephant or a shrew, has the biggest surface are to volume ratio. Explain your answer.

  Shrew - Small animals have a larger surface area compared to their volume, so they lose heat more readily.
• What is the relationship between surface area to volume ratio and an animal’s metabolic rate?

  As a general rule, the greater the mass of an organism the higher that organism’s metabolic rate is as they require more efficient delivery of oxygen to cells.
• Volume of a Sphere = 4/3 x pi x r^3
• Surface Area of a Sphere = 4 x pi x r^2
• Volume of a Cylinder = pi x r^2 x height
• Surface Area of a Cylinder = (2 x pi x r x h) + (2 x pi x r^2)
• Describe the relationship between the size and surface area to volume ratio of organisms.

  As the size of organisms increases, their surface are to volume ratio decreases.
• Explain why oxygen uptake is a measure of metabolic rate in organisms.


  Oxygen is used in respiration which is a metabolic process.