Answer:
<u>Active transport across membranes is like refilling an empty soda can after pouring the soda into a cup. It takes effort (energy in the form of ATP) to pour the soda back into the can, it wouldn't typically happen on its own.</u>
Explanation:
Cells use several transport mechanisms to move substances across their plasma membranes. Plasma membranes control all movement of substances through passive transport, which does not use energy; and active transport which requires chemical energy in the form of ATP.
Active transport moves substances out of cells against their gradients. In the cell, glucose can be transported inwards for respiration. However, because the internal environment is typically concentrated, (and glucose is needed in high amounts) this requires the use of transport enzymes and ATP.
