Exchange Surfaces Flashcards
How do you work out SA:V (Surface Area to Volume Ratio) ?
Cube (shape) —–
1) Surface area : (Length x Width) x number of equal surfaces
2) Volume : Length x Width x Height
3) To simplify, divide both sides of the ratio by the volume.
How are exchange surfaces adapted to maximise effectiveness?
They have a thin membrane, so substances only have a short distance to diffuse.
They have a large surface area so lots of a substance can diffuse at once.
Exchange surfaces in animals have lots of blood vessels, to get substances into and out of the blood quickly.
Gas exchange surfaces in animals are often ventilated.
Why are exchange surfaces needed in multicellular organisms?
Multicellular organisms have a smaller surface area compared to their volume. So not enough substances can diffuse from their outside surface to supply their entire volume. This means they need some sort of exchange surface for efficient diffusion. The exchange surface structures have to allow enough of the necessary substances to pass through.
Why are exchange surfaces needed in single-celled organisms?
In single-celled organisms, gases and dissolved substances can diffuse directly into or out of the cell across the cell membrane. It’s 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.
How are substances such as oxygen, carbon dioxide and urea transported in and out of cells by diffusion?
Oxygen and carbon dioxide are transferred between cells and the environment during gas exchange.
In humans, urea diffuses from cells into the blood plasma for removal from the body by the kidneys.
