surface area to volume ratio

• What concept explains why multicellular organisms require exchange surfaces and a transport system?

  The surface area to volume ratio
• What is the function of gills in fish?

  To increase the rate of transport of gases into and out of fish
• How do molecules move in and out of cells?

  By diffusion
• What is an example of a molecule that diffuses into cells?

  Oxygen
• What is an example of a molecule that diffuses out of cells?

  Carbon dioxide
• What is the surface area to volume ratio?

  It is a measure of the amount of surface area available relative to the volume of an organism
• If an organism shaped like a cube has a side length of 1 mm, what is its surface area?

  6 square mm
• If the volume of a cube-shaped organism with a side length of 1 mm is calculated, what is the volume?

  1 cubic mm
• What is the surface area to volume ratio of a cube with a side length of 1 mm?


  1. 1
• For a cube with a side length of 2 mm, what is the surface area?

  24 square mm
• What is the volume of a cube with a side length of 2 mm?

  8 cubic mm
• What is the surface area to volume ratio of a cube with a side length of 2 mm?

  1. 1
• For a cube with a side length of 3 mm, what is the surface area to volume ratio?

  1. 1
• Why do multicellular organisms face a problem with gas exchange?

  Their surface area is not large enough for their volume
• How do animals solve the problem of gas exchange?

  By having special structures for gas exchange and a transport system
• What are the special structures for gas exchange in mammals?

  Lungs
• How do fish obtain oxygen from water?

  Oxygen-rich water passes into the mouth and flows over gills
• What happens to deoxygenated blood in fish gills?

  It passes into the filaments where oxygen diffuses from the water into the blood
• Why is a high concentration gradient important in fish gills?

  It ensures that diffusion is as efficient as possible
• What adaptations do gill filaments have to increase the rate of diffusion?

  They have a massive surface area, a thin membrane, and an efficient blood supply
• What is the relationship between surface area to volume ratio and organism size?

  • As organisms get larger, the surface area to volume ratio decreases sharply
  • This presents challenges for gas exchange in multicellular organisms
• What are the key adaptations of gills for gas exchange in fish?

  • Massive surface area
  • Thin membrane for short diffusion pathway
  • Efficient blood supply to maintain concentration gradient