Portal:Biology/Featured

"The active transport of small molecules or ions across a cell membrane is generally carried out by transport proteins or “pumps” that are found in the membrane itself. Larger molecules and clumps of material can also be actively transported across the cell membrane by processes known as endocytosis and exocytosis. The transport of these larger materials sometimes involves changes in the shape of the cell membrane.
 * --Read more about active transport in High School Biology/Lessons/Lesson 3, taught by AvidInsight.