How are different substances transported across the cell membrane?

There are several different ways substances can be transported:

1) simple diffusion, i.e. substances that tend to be lipid soluble/ non-polar and can pass easily across the phospholipid bilyar of cells.                                                                                                                                                                   2) facilitated diffusion, which involves ihe roles of carrier proteins and channel proteins. E.g. oxygen and glucose       3) osmosis ( water is transported from an area of higher water potential to a lower water potential across a membrane.                                                                                                                                                                       4) active transport- involves the transport of substances against a concentration gradient and uses carrier proteins and ATP hydrolysis is required. An example of this is a sodium-potassium pump after an action potential.                     5) co-transport- this is when substances are simultaneously transported across a membrane by one protein e.g. the absorption of sodium ions and glucose by cells lining the mammalian ileum.