Simple Definition:

Endocytosis is a process in which a cell takes in (engulfs) external substances (particles or molecules) by forming a pocket-like structure called a vesicle (a small sac) that brings the substances into the cell. This process is used by cells to obtain nutrients, remove waste materials, or regulate various cellular processes.

Examples:

• When a white blood cell engulfs (takes in) a bacterium to destroy it, it is using endocytosis.
• During the process of nutrient absorption in the small intestine, cells lining the intestine use endocytosis to take in (absorb) nutrients from the digested food.

Very Simple Definition:

Endocytosis is a process in which a cell brings things inside itself. The cell forms a small sac called a vesicle to do this. It helps the cell get what it needs or get rid of things it doesn’t want.

Examples:

• When a whie blood cell eats a harmful germ, it uses endocytosis.
• Cells in our body use endocytosis to drink up nutrients from our food.