surface area to volume ratio

• Surface area to volume ratio

  Measure of how big the surface area is compared to the volume of an organism
• As organisms get larger

  Their surface area to volume ratio decreases
• Larger organisms have less surface area compared to their volume
• Calculating surface area of a cube


  Calculate area of one face, then multiply by 6 (number of faces)
• Calculating volume of a cube

  Multiply length, width and height
• As cubes get larger


  Volume increases much more quickly than surface area
• Bacteria have a high surface area to volume ratio
• Humans have a low surface area to volume ratio
• Bacteria


  • Can rely on diffusion across their surface to exchange substances
• Humans


  • Cannot rely on diffusion alone, require specialized exchange surfaces like lungs and intestines
• Humans


  • Require transport systems like circulatory system to transport substances around body
• Plants have roots and leaves to exchange substances, and phloem and xylem to transport substances
• When we say "large organisms", we mean anything big enough to see with the naked eye, not just humans and cows
• Even insects like mosquitoes have exchange and transport systems