SA:VR

• how does a single- celled organism survive? absorbs: oxygen. glucose , amino acids gets rid of: carbon dioxide
• as organisms get larger.... their SA:VR decreases
• how to calculate SA of an object? area of a face x number of faces
• how to calculate volume of an object? lxwxh
• what does it mean if bacteria cells have a high SA:VR?

  they reply on diffusion to exchange substances they need
• what does it mean if humans have a low SA:VR?

  cant reply on diffusion so they need specialised organisms to exchange substances like alveolis and villis
• as organisms get larger...

  the distance that molecules would have to diffuse to get from the outside to the inside of the body increases massively
• Downsides of a larger organisms -

  lower SA:VR= diffusion will be slower

  but have transport systems like the circulatory system =molecules travel short distances to get into cell
• what do larger and plant organisms have?

  exchange and transport systems