Cell Transport

Like a castle wall, the semi-permeable cell membrane guards the entry and exit of substances into and out of the cell.

The phospholipid bilayer allows small molecules like oxygen and carbon dioxide to diffuse freely.

For ions and larger molecules, like glucose and starch, specialized proteins called carrier proteins and channels help them move across the membrane.

Channels are like tunnels that let molecules like water or ions pass through freely, as long as they are the right size and shape. If they fit and the channels are open, they can pass through.

Carrier proteins, such as glucose carriers, bind to specific molecules, change shape, and carry the molecules across the membrane.

If the membrane allowed everything to pass through it, the inside of the cell would become identical to its external environment.

The cell would lose its ability to maintain its chemical balance and structural integrity.