Here's why:
* Active transport is the movement of molecules across a cell membrane against their concentration gradient, meaning from an area of lower concentration to an area of higher concentration. This requires energy, usually supplied by ATP.
* Expansion refers to an increase in size. While cells can grow and expand, this is a separate process from active transport.
Instead of expanding, a cell uses the following to accomplish active transport:
* Membrane proteins: These proteins act as pumps or carriers, using energy to bind to and move molecules across the membrane.
* ATP: Adenosine triphosphate is the primary energy source for cells and is used to power the movement of molecules against their concentration gradients.
Think of it like this: Imagine you're trying to push a rock uphill. It takes effort (energy) to move it against gravity. Similarly, active transport requires energy to move molecules against their concentration gradient.
Let me know if you have any other questions!
