What is endocytosis ?

Explanation

**Step-by-Step Solution:**

1. **Definition of Endocytosis**: Endocytosis is a biological process through which cells take in substances from their external environment by engulfing them with their plasma membrane.

2. **Direction of Transfer**: In endocytosis, materials are transferred from the outside environment into the interior of the cell. This process allows cells to intake nutrients, fluids, and other necessary substances.

3. **Example of Endocytosis**: A classic example of endocytosis can be observed in amoeba, a single-celled organism. Amoeba uses a method called phagocytosis, a type of endocytosis, to obtain nutrition.

...