Facilitated Diffusion and Active Transport
Facilitated diffusion is a special form of diffusion which allows rapid exchange of specific substances. Particles are taken up by carrier proteins which change their shape as a result. The change in shape causes the particles to be released on the other side ...
Facilitated Diffusion
Facilitated diffusion is a special form of diffusion which allows rapid exchange of specific substances. Particles are taken up by carrier proteins which change their shape as a result. The change in shape causes the particles to be released on the other side of the membrane.
Facilitated diffusion can only occur across living, biological membranes which contain the carrier proteins. A substance is transported via a carrier protein from a region of high concentration to a region of low concentration until it is randomly distributed. Therefore movement is down a concentration gradient.
Image credit: Siyavula
Examples of substances moved via facilitated diffusion include all polar molecules such as glucose or amino acids.
Active Transport
Active transport is the movement of substances against a concentration gradient, from a region of low concentration to high concentration using an input of energy. In biological systems, the form in which this energy occurs is adenosine triphosphate (ATP). The process transports substances through a membrane protein. The movement of substances is selective via the carrier proteins and can occur into or out of the cell.
Fact:
ATP and ADP are molecules involved with moving energy within cells. You do not need to know these names in full and will learn more about them later.
Image credit: Siyavula
Examples of substances moved include sodium and potassium ions as shown in the figure above.
Video: Cell Membranes and Cell Transport
The Amoeba Sisters video below explores the types of passive and active cell transport.
This lesson is part of:
Introducing the Cell