Why is energy needed for active transport? a. molecules are moving against a concentration gradient. b. molecules are moving into an isotonic environment. c. molecules are moving against membrane proteins. d. molecules are moving through a bipolar cell membrane.

The correct answer is A. Molecules are moving against a concentration gradient.

Active transport is a process in which molecules move from a medium of low concentration gradient to a medium of high concentration gradient across the cell membrane. Since molecules move against the concentration gradient, therefore, this process requires energy.

Active transport is primarily divided into two types-

Primary active and secondary active transport.

In primary active transport, metabolic energy is used directly ( Example- hydrolysis of ATP)

In secondary active transport, energy is utilized by the movement of one molecule along the concentration gradient. This movement is coupled with another molecule, which moves against the gradient.

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