Exchange Surfaces

• An organism's survival depends on its interaction with the environment, taking in useful substrates like nutrients and excreting waste products.
• The exchange of substances between an organism and its environment must be finely balanced for the organism to maintain a suitable and stable internal environment.
• Single-celled organisms like bacteria can easily exchange substances with the external environment through their cell walls because they are very small and have a large surface area to volume ratio.
• When bacteria carry out respiration, the oxygen they need diffuses straight into their cell from the outside air, and the carbon dioxide which they produce as waste can then diffuse straight back out into the atmosphere.
• As organisms get bigger, their surface area to volume ratio falls and the rate at which they can diffuse substances to all of their cells also falls.
• Before long, larger organisms reach a point where they can no longer rely solely on diffusion within environments because it would take too long to get everything that they need to all of their cells.
• The surface area to volume ratio of a mouse is six to one, while that of an elephant is six hundred to one thousand or zero point six to one.
• The larger the organism, the smaller its surface area to volume ratio is going to be.
• Larger organisms require specialized exchange systems rather than just relying on diffusion.
• Exchange surfaces have a large surface area relative to their volume, very thin membranes, permeable membranes, and a diffusion gradient for particles to diffuse down.