Endocytosis is a cellular process where cells absorb molecules or substances from outside the cell by engulfing it with the cell membrane.

This technique is critical to the survival of the cell, since most molecules important to the cell cannot normally pass through the cell's hydrophobic plasma membrane.

Endocytosis is the opposite of exocytosis.

There are three types of endocytosis:

In this process, the cell membrane folds around the molecule or substance, and it is dissolved into the interior of the cell.

Molecules such as proteins and other water-soluble substances are thus injested this way, which could not otherwise breach the cell membrane. (Pinocytosis is literally translated as "cell drinking.")

This process is similar to phagocytosis, except that the cell uses receptor proteins embedded within the cell membrane.

These proteins target specific molecules or substances, attracting then seizing hold of them and pulling them into the cell within a fold of the cell membrane.

Cholesterol is absorbed from our bloodstream by cells using receptor-mediated endocytosis.

Check out these resources for more information about cell membranes:

• Active Transport
• Passive Transport
• Carrier Proteins
• Membrane Proteins
• Lipid Bilayer
• Endocytosis
• Exocytosis
• Diffusion Through a Membrane
• Osmosis in a Plant Cell
• Osmosis in an Animal Cell
• Plasma Membrane - Plant Cell
• Plasma Membrane - Animal Cell
• My Cell Membranes flashcards
• Biology Quiz: Cell Membranes