Gas and solute exchange

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Substances move by osmosis, active transport and diffusion.

Life processes need gases or different dissolved substances before they can take place.
e.g. photosynthesis needs CO2 and H2O inside plant cells,
and respiration needs glucose and oxygen inside cells to happen.

Waste substances also need to move so that an organism can get rid of them.

Diffusion- particles move down the concentration gradient

Active transport moves substances in the other direction using carrier proteins.

In life processes the gases and dissolved substances have to pass through an exchange surface. The exchange surface structures have to allow enough of the substance through for the process to take place.

Exchange surfaces are adapted to maximise effectiveness:

  • thin, so substances have short distance to diffuse
  • large surface area > lots of substances can diffuse at once
  • animals > lots of


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