Biology, Eighth Edition (Raven)

Chapter 5: Membranes

Primary Active Transport

Why is energy needed for active transport? Active transport moves molecules up a concentration gradient, generating potential energy across a membrane. That energy must come from somewhere. Active transport converts energy stored in chemical bonds into energy stored in a concentration gradient. When ATP reacts with the transport protein the energy stored in a phosphate-phosphate bond is released. The reaction of the phosphate with the transport protein changes the shape of the transport protein, moving the molecule across the membrane. The energy is thus transferred from the ATP to the transport protein and then to the concentration gradient.

View the animation below, then complete the quiz to test your knowledge of the concept.



1.

Active transport requires...
A)an enzyme on the surface of the cell.
B)a channel on the surface of the cell.
C)a carrier protein on the surface of the cell.
D)a pore on the surface of the cell.
E)a gate on the surface of the cell.
2.

Active transport moves a solute...
A)up its concentration gradient, that is, from a low concentration to a high one.
B)up its concentration gradient, that is, from a high concentration to a low one.
C)down its concentration gradient, that is, from a low concentration to a high one.
D)down its concentration gradient, that is, from a high concentration to a low one.
E)across its concentration gradient, that is, from a high concentration to a low one.
3.

Active transport requires...
A)energy in the form of ADP.
B)energy in the form of ATP.
C)energy in the form of glucose.
D)energy in the form of fructose.
E)little or no energy to function.
4.

Once the solute molecule is in the binding site, a phosphate disengages from the binding molecule and the solute is released.
A)True
B)False
5.

Active transport is able to move these substances without the expenditure of energy.
A)True
B)False
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