Active Transport

Active transport is when molecules move "up" the concentration gradient, or from low to high concentration. This does require ATP energy from the cell.

Learn about 3 types of Active Transport below!

Protein Pumps

Protein pumps are protein structures in the cell membrane that change shape to pump ions like Na+ (sodium) and K+ (potassium) through the membrane. These ions cannot travel through the lipid bilayer alone.

These ions travel "up" the concentration gradient, or from low concentration to high concentration.

For the protein pumps to change their shape and push the ions through, ATP energy from the cell is required.

One example is the sodium-potassium pump.

The animation on the left can help you visualize this process.

Endocytosis

Endocytosis is the process of a cell capturing a substance or particle from outside the cell by engulfing it with the cell membrane. This is when a cell needs to take something in that is too big to fit through the cell membrane. (Think "endo" = "into")

The cell membrane folds over the substance and it becomes completely enclosed by the membrane. At this point a membrane-bound sac, or vesicle, pinches off and moves the substance into the cytoplasm.

Endocytosis requires ATP energy from the cell.

Examples include amoebas eating and white blood cells engulfing foreign matter.

Watch the animation and videos of real cells to visualize this process.

Exocytosis

Exocytosis is the opposite of endocytosis. (Think "exo" = "exit") Exocytosis is the process of :

a small membrane-bound vesicle forms within the cell
the vesicle fuses with the plasma membrane
the vesicle releases the contents to the outside of the cell

Exocytosis occurs when a cell produces substances for export, such as a protein, or when the cell is getting rid of a waste product or a toxin, and these substances are too big to fit through the cell membrane.

Exocytosis requires ATP energy from the cell.

Examples include the cell releasing digestive enzymes or waste.

Watch the animation and video of a real cell to visualize this process.

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