To survive, every living cell must constantly take in the chemicals it needs and let out the ones it does not need through its thin membrane (casing). Cells do this in several ways, including osmosis, diffusion and active transport.
Osmosis is when water moves to even the balance between a weak solution and a stronger one.
Diffusion is when the substances that are dissolved in water or mixed in air move to even the balance.
Osmosis happens when the molecules of a dissolved substance are too big to slip through the cell membrane – only the water is able to move.
Osmosis is vital to many body processes, including the workings of the kidney and the nerves.
Urine gets its water from the kidneys by osmosis.
In diffusion, a substance such as oxygen moves in and out of cells, while the air or water it is mixed in mainly stays put.
Diffusion is vital to body processes such as cellular respiration, when cells take in oxygen and push out waste carbon dioxide.
Active transport is the way a cell uses protein-based ‘pumps’ or ‘gates’ in its membrane to draw in and hold substances that might otherwise diffuse out.
Active transport uses energy and is how cells draw in most of their food such as glucose.