exchange surfaces

• how easily an organism exchanges substances with its enviroment depends on the organisms surface area to volume ratio, cells use diffusion to exchange substances with their environment (e.g oxygen and carbon dioxide during gas exchange)
• surface area equation:

  surface area = length * width
• volume equation:

  volume = length * width * height
• the larger an organsim is the smaller its surface area is compared to its volume
• single-celled organisms have a large surface area to volume ratio, so they can exchange large amounts of substances

  multicellular organisms have a smaller surface area to volume ratio, so they need an exchange surface for efficient diffusion (so enough necessary substances can pass through)
• exchange surfaces are adapted to maximise the rate of diffusion:

  1. have a thin membrane (only a short distance to diffuse)
  2. have a large surface area (lots of diffusion at once)
  3. in animals they have lots of blood vessels (get substances in/out of the blood quickly)
  4. gas exchange surfaces in animals (e.g alveoli) are often ventilated (maintains a steep concentration gradient so diffusion happes quickly)