Cell membranes act like gates, controlling what goes in and out of the cell. They do this through two main processes: active transport and passive transport.

1. Passive Transport: This process allows molecules to move without using any energy. Here are two examples:

   • Diffusion: This is when tiny particles, like oxygen, move from areas where there are a lot of them to areas where there aren’t as many.
   • Osmosis: This is the movement of water through the cell membrane. It helps balance the amounts of water on both sides.

2. Active Transport: This process needs energy (called ATP) to move things against their natural flow. A good example is the sodium-potassium pump, which helps keep the right balance of important ions.

Both of these processes work together to help cells stay stable, keeping what they need in and getting rid of waste.