Which of the following is a characteristic of active transport? check all answers that apply.
a. it moves substances along a concentration gradient.
b. it moves substances against a concentration gradient.
c. it requires energy from the cell.
d. it does not require energy from the cell.

The following are characteristics of active transport:

B) It moves substances against a concentration gradient.

C) It requires energy from the cell.

Active and Passive Transport

Passive transport is the movement of particles through a membrane which requires no extra energy. It happens spontaneously because there is an imbalance in the amount of solutes  or difference in concentration inside and outside the membrane. In order to reach equilibrium or a state where the amount of solute or concentration on both sides is the same, some substances have to cross the membrane.

When substances move from a region of high concentration to low concentration, it is said that the substances are moving down a concentration gradient. This process is spontaneous meaning it does not require energy to occur. The opposite is true for active transport which requires additional energy for it to happen.

Movement of Substances (Passive Transport)

In diffusion, solutes move from a concentrated area to a less concentrated area.

In osmosis, the water molecules move from an area with more water molecules (lower concentration of solutes) to the area with less water molecules (higher concentration of solutes).

Keywords: osmosis, diffusion, active transport

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