What is endocytosis?

• A. The process by which cells expel materials to the outside environment.
• B. The process of synthesizing proteins within the cell.
• C. The process of cell division resulting in two daughter cells.
• D. The process by which cells engulf external substances, bringing them into the cell.

Answer: (D)

Verified step by step guidance

1. Endocytosis is a cellular process where cells internalize substances from their external environment.
2. This process involves the cell membrane folding inward to form a pocket around the external material.
3. Once the pocket is formed, the membrane pinches off to create a vesicle containing the engulfed material.
4. Endocytosis can be categorized into different types, such as phagocytosis (engulfing large particles) and pinocytosis (engulfing liquids).
5. This mechanism is crucial for nutrient uptake, immune responses, and cellular signaling.