Final answer:
Large molecules such as food particles enter or exit a cell through endocytosis or exocytosis, forms of active transport that require energy in the form of ATP.
Step-by-step explanation:
When large molecules such as food particles need to get into a cell, they cannot easily pass through the plasma membrane. Therefore, these molecules move across the membrane through the processes known as endocytosis and exocytosis. These are forms of vesicle transport, which is an active transport process requiring energy.
Endocytosis is the process where the cell membrane engulfs a particle and pinches off to form a vesicle internally transporting the particle into the cell. This includes phagocytosis (cell eating) for large particles or cells, and pinocytosis (cell drinking) for liquids, and receptor-mediated endocytosis for specific molecules. Conversely, exocytosis involves the fusion of vesicles with the plasma membrane to expel materials from the cell. Both mechanisms are crucial since large polar molecules and charged particles cannot freely cross the hydrophobic core of the cell membrane. Hence, cells have evolved these specialized mechanisms to manage the import and export of large substances, requiring ATP to carry out these functions.