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Active transport review

Key terms

Active transportType of transport that requires an input of energy to occur
Concentration gradientA region of space over which the concentration of a substance changes
ATPAdenosine triphosphate, the primary energy carrier in living things

Active transport

During active transport, substances move against the concentration gradient, from an area of low concentration to an area of high concentration. This process is “active” because it requires the use of energy (usually in the form of ATP). It is the opposite of passive transport.
Image credit: OpenStax Biology. Image modified from original work by Mariana Ruiz Villareal.
Active transport requires assistance from carrier proteins, which change conformation when ATP hydrolysis occurs.

Common mistakes and misconceptions

  • Active transport is not the same as facilitated diffusion. Both active transport and facilitated diffusion do use proteins to assist in transport. However, active transport works against the concentration gradient, moving substances from areas of low concentration to areas of high concentration. In addition, the types of proteins that they use are different. (See below.)
  • Active transport uses carrier proteins, not channel proteins. These carrier proteins are different than the ones seen in facilitated diffusion, as they need ATP in order to change conformation. Channel proteins are not used in active transport because substances can only move through them along the concentration gradient.

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