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Active transport review

AP.BIO:
ENE‑2 (EU)
,
ENE‑2.E (LO)
,
ENE‑2.E.3 (EK)
,
ENE‑2.G (LO)
,
ENE‑2.G.3 (EK)

Key terms

TermMeaning
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.
Figure showing the transport cycle of the sodium-potassium pump.
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.

Want to join the conversation?

  • blobby green style avatar for user Monica
    is sweating a form of active transport
    (9 votes)
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    • orange juice squid orange style avatar for user Ross
      I think that sweating is a form of passive transport as heat that is generated in the cells inside your skin is moving WITH the concentration gradient from hot (inside) to cold (outside). I think that's right. I haven't yet studied the videos on perspiration.
      (21 votes)
  • hopper cool style avatar for user Moksha
    What is the difference between facilitated diffusion and active transport?
    (5 votes)
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  • spunky sam green style avatar for user Abhranil
    what is hydrophillic and hydrophobic? Please answer
    (3 votes)
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  • aqualine ultimate style avatar for user Emily
    Are the largest molecules moved by only active transport or also by passive?
    (5 votes)
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    • blobby green style avatar for user hirapanna0616
      No, actually both facilitated diffusion and active transport occur. When the molecules moving from high to low conc. like Glucose is very large, then we need channel proteins to move them into the cell, and channel protein only because they have the shape and structure to do so, so that the movement is only unidirectional (into the cell). Active transport transports or moves materials against the concentration gradient, that is, from low to high, and the size doesn't matter here like facilitated diffusion, only the concentration.
      (3 votes)
  • duskpin sapling style avatar for user 🎅🏿Parker🎄
    I don't understand active and passive transport i need help.
    (3 votes)
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    • hopper happy style avatar for user loganpope
      Active transport uses energy to transport molecules across the plasma membrane. This uses energy from ATP. They also use pumps to get molecules in or out of the cell. Passive Transport does NOT use energy to transport molecules across the membrane. This can also just be molecules diffusing across the permeable membrane or a direct channel which they can enter or exit.
      (5 votes)
  • hopper jumping style avatar for user Harry Potter
    How do carrier/channel proteins select which particles to pass through and when?
    More specifically,
    How do aquaporins only let water in? How can the cell control the amount of water that can diffuse through aquaporins? How come the channel protein will not bring in potassium ions when it needs to bring in sodium ions?
    (4 votes)
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    • aqualine ultimate style avatar for user Yaelle
      Hi ! The shapes of the channels is very specifically adapted to letting only one type of molecules through. For example, aquaporins are shaped in a way that only water can pass through (because water has a specific structure and charge). Sodium and potassium do not have the same size nor shape and therefore one cannot use the channel of the other as well.
      The cell can control the amount of water that it lets in or out, by controlling the amount of aquaporins in its membrane. This is done by exocytosis/endocytosis of aquaporins, that can be controlled for example by antidiuretic hormons (that tend to provoke endocytosis of aquaporins).
      (3 votes)
  • blobby green style avatar for user ariellalepis98
    Why is it beneficial for the body to use energy to move something against its concentration gradient? What's the point of creating this imbalance of positive charges?
    (3 votes)
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    • piceratops tree style avatar for user Adeoluwa
      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.
      (3 votes)
  • blobby green style avatar for user 318604
    what is facilitated diffusion
    (3 votes)
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  • blobby green style avatar for user Brooke Walsh
    Particles have a lot of energy built in...what type of energy allows t
    hem to move (such as in this process of diffusion)?
    (3 votes)
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    • blobby green style avatar for user hirapanna0616
      Diffusion is pssive transport, it doesn't require energy to move materials. If you consider the molecules, they move by kinetic energy, probably gained by the motion of their circulation throughout the system, or due to the concentration gradient.
      (0 votes)
  • blobby green style avatar for user nmarpita1983
    What are the differences between a carrier and a channel protein? Also, what are some examples?
    (1 vote)
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