6.1 SA:Vol

• As the size of the cube/organism increases the SA:Vol ratio gets smaller
• The surface area to volume (SA:V) ratio is important because it determines how much material can be exchanged per unit time.
• In single cellular organisms SA: Vol is very large in comparison to their volume
• Multi cellular organisms are evolved to have adaptations to increase their surface area (makes it larger).
• Multi cellular organisms have adapted to have specialised exchange systems to transport substances around the body.
• Diffusion is the movement of particles from high conc to low conc until equilibrium is reached.
• Name 3 features of specialised exchange surfaces.

  1. Large SA:Vol
  2. Very thin
  3. Selectively permeable
• Why do specialised exchange surfaces have a large SA:Vol?

  To increase the rate of exchange
• Why are specialised exchange surfaces very thin?

  So that the diffusion distance is short and therefore the rate of exchange will increase.
• Why are specialised exchange surfaces selectively permeable?

  To allow selected materials to cross
• Because small organisms have a very large SA in comparison to their Vol it means that

  1. Bigger surface for exchange of substances
  2. Smaller distance from the outside of the organism to the middle of it
• Give an example of a single cellular organism.

  Amoeba
• Larger organisms have a higher metabolic rate, what does this mean?

  Chemical reactions within a cell are happening faster
• A reason why larger organisms have to have adaptions for transport is because they have a higher metabolic rate (chemical reactions within a cell are happening faster) compared to smaller organisms.
• What adaptions increase SA:Vol in absorption of digested food?

  Villi and microvilli
• What adaptions increase SA:Vol in gas exchange for Mammals?

  Alveoli and bronchioles in the lungs.
• What adaptions increase SA:Vol in gas exchange for Insects?

  Spiracles and tracheoles
• What adaptions increase SA:Vol in gas exchange for Fish?

  Gill filaments and lamellae
• What adaptions increase SA:Vol in gas exchange for plants?

  Thin and wide leaves