Surface Area to Volume Ratio

• SURFACE AREA:

  • TRANSFER: Surface area to vol ratio influences how substances & heat energy can be transferred around organisms
  • SA= total surface area over which substances & heat can be exchanged. SA alone cant influence rate of exchange
• VOLUME:

  • METABOLISM: As the vol increases, more substances are needed for metabolism as there are more cells
• SA TO VOL RATIO:

  • INCREASED SIZE: When an organism increases in size -> its vol increase at a faster rate than its surface area (as there are more cells)
  • CELLS IN CONTACT; The increase in the number of cells -> less surface area for exchange of materials as many cells are in contact with others
  • ORGANISM SIZE: The SA to vol ratio decreases with increasing organism size
• Adaptations to SA to Vol ratio

  • Large SA allows more of a substance to diffuse at the same time
  • Thin membrane reduces the diffusion distance
  • Transport systems move substances around the organism/ facilitate exchange (e.g. blood vessels, lungs, gills, xylem)
  • Transport systems allow a higher concentration gradient to be maintained (steep concentration increases rate of transport)
  • Transport systems allow substances to move closer to cells that need to exchange them
  • Some animals have adaptations to allow quick heat transfer (e.g. elephants' highly vascularised ears)
  • Specialised exchange surfaces are thin so easily damaged/dehydrated, located on the inside of an organism