Answer: Cell membrane
Step-by-step explanation:
The cell membrane plays a crucial role in controlling what goes in and out of a cell. This includes maintaining the cell's shape, protecting the cell from damage, and allowing for the movement of nutrients and waste materials, among other functions. The cell membrane is a selective filter that allows some substances to enter and leave, while keeping out others. It also has specialized proteins that allow specific substances to be transported across it, such as pump proteins that pump ions across the membrane. The cell membrane is one of the most important structures in a cell, as it allows the cell to maintain homeostasis and survive.