Passive Transport

Describe passive transport and explain its role in cellular systems

Passive transport is the movement of substances across a membrane without the expenditure of energy. Diffusion, facilitated diffusion, filtration, and osmosis are examples of passive transport. In cellular systems this is a very important action, because all ATP created by a cell is very precious, the more it can reserve and use for other purposes, the better. Essential substances such as lipids, water, oxygen, and small monosaccharides can pass through via passive transport and give the cell the materials it needs, without causing it to work overtime for it. Water, for example, is a very important substance in all cells. [See ‘-tonic’ under Ch 7 for more details on the importance of water in cells] Because water can diffuse in and out of cells passively, a cell is able to maintain its internal environment without exerting too much energy.