Surface Area to Volume Ratio

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

  Surface area to volume ratio
• Why do single-celled organisms like amoebas rely on diffusion for transport?

  They have a large surface area for their volume, allowing effective diffusion.
• What is the relationship between surface area to volume ratio and organism size?

  • As organisms increase in size, their surface area to volume ratio decreases.
  • Larger organisms face challenges in gas exchange due to insufficient surface area.
• What is the surface area to volume ratio of a cube with a side length of 1 mm?

  6:1
• How would you calculate the surface area to volume ratio of a cube with a side length of 2 mm?

  3:1
• What happens to the surface area to volume ratio as the size of an organism increases?

  It decreases.
• What are the two solutions multicellular organisms have developed to address the problem of gas exchange?

  • Special structures for gas exchange with high surface area (e.g., lungs in mammals).
  • A transport system to carry gases throughout the body.
• How do fish obtain oxygen from water?

  Oxygen-rich water passes into the mouth and flows over the gills.
• What is the purpose of this video?

  By the end of this video, the viewer should be able to use the idea of surface area to volume ratio to explain why multicellular organisms require exchange surfaces and a transport system, and describe how gills increase the rate of transport of gases into and out of fish.
• What is a key fact linked to the idea of diffusion?

  The surface area to volume ratio is a key fact linked to the idea of diffusion.
• Why can single-celled organisms like the amoeba rely on diffusion to transport molecules in and out of their cell?

  Single-celled organisms have a high surface area to volume ratio, which allows them to rely on diffusion to transport molecules in and out of their cell.
• What could you be asked to do in an exam regarding the surface area to volume ratio?

  You could be asked to calculate the surface area to volume ratio of an organism.
• How do you calculate the surface area to volume ratio of a cube-shaped organism?

  1. The length of each side is 1 mm.
  2. The area of each side is 1 mm * 1 mm = 1 square mm.
  3. There are 6 sides, so the total surface area is 6 square mm.
  4. The volume is 1 mm * 1 mm * 1 mm = 1 cubic mm.
  5. The surface area to volume ratio is 6:1.
• What is the surface area to volume ratio of an organism with 2 mm side lengths?

  3:1
• What happens to the surface area to volume ratio as organisms get larger?

  The surface area to volume ratio decreases sharply as organisms get larger.
• Why is the decreasing surface area to volume ratio a problem for multicellular organisms?

  • Cells on the surface can get enough oxygen by diffusion.
  • However, cells in the center of the organism are too far away from the surface, so not enough oxygen can diffuse into them.
• How have animals solved the problem of decreasing surface area to volume ratio?

  1. They have special structures for gas exchange with a very high surface area, such as lungs.
  2. They have a transport system to carry gases around the body.
• How do fish get their oxygen?

  • Oxygen-rich water passes into the mouth and flows over the gills.
  • Oxygen is transported into the bloodstream through the gills.
• What are the three adaptations of fish gills that increase the rate of gas diffusion?

  1. Gills have a massive surface area due to the fine filaments.
  2. The filaments have a thin membrane to provide a short diffusion pathway.
  3. The filaments have an efficient blood supply to take the oxygenated blood away, maintaining a high concentration gradient.