A complex or undefined medium is rich in nutrients, which contain water-soluble extracts of plant or animal tissue, a sugar, (often glucose is added to serve as the main carbon and energy source). The combination of extracts and sugar creates a medium which is rich in minerals and organic nutrients, but the exact composition is unknown.
<span>Substances can move into and out of cells through the cell membrane. The three main types of movement are diffusion, osmosis and active transport.</span>
