Exchange Surfaces Flashcards
How can cells take in substances they need and get rid of waste products? Give two examples.
Cells can use diffusion to do this. For example, 1. Oxygen and carbon dioxide are transferred between cells and the environment during gas exchange. 2. In humans, urea (a waste product) diffuses from cells into the blood plasma for removal from the body by the kidneys.
How easy it is for an organism to exchange substances with its environment depends on the organism’s_?
surface area to volume ratio (SA : V).
The larger an organism is,_?
the smaller its surface area is compared to its volume.
Why, in single-celled organisms, can gases and dissolved substances diffuse directly into (or out of) the cell across the cell membrane?
Because they have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to supply the volume of the cell.
Why can’t substances in multicellular organisms diffuse directly just like single-celled organisms? What do they do instead?
Multicellular organisms have a smaller surface area compared to their volume - not enough substances can diffuse from their outside surface to supply their entire volume. Instead, they need to do some sort of exchange surface for efficient diffusion. The exchange surface structures have to allow enough of the necessary substances to pass through.
In what ways are exchange surfaces adapted to maximise effectiveness?
- They have a thin membrane, so substances only have a short distance to diffuse. 2. They have a large surface area so lots of a substance can diffuse at once. 3. Exchange surfaces in animals have lots of blood vessels, to get stuff into and out of the blood quickly. 4. Gas exchange surfaces in animals (e.g. alveoli) are often ventilated too - air moves in and out.
