Endocytosis:
Endocytosis is the process by which cells take in substances from outside of the cell by engulfing them in a vesicle formed from the cell membrane.

Example of amoeba:
Amoeba is a unicellular organism that uses endocytosis to obtain food. It engulfs food particles by extending its pseudopodia around them and forming a food vacuole. The vacuole then fuses with lysosomes, which contain digestive enzymes, to digest the food. The nutrients are then absorbed into the cell.

Types of Endocytosis:
There are three types of endocytosis:

1. Phagocytosis: This type of endocytosis is used by cells to take in large particles such as bacteria, dead cells, and other debris. Amoeba use phagocytosis to obtain food.

2. Pinocytosis: This type of endocytosis is used by cells to take in small particles such as ions and molecules dissolved in the surrounding fluid.

3. Receptor-mediated endocytosis: This type of endocytosis is used by cells to take in specific molecules that bind to receptors on the cell membrane.

Conclusion:
Endocytosis is an important process that allows cells to take in nutrients, remove debris, and regulate their environment. Amoeba is an example of a unicellular organism that uses endocytosis to obtain food. There are three types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis.