What are the bad things that are not allowed into a cell?

Answer 1

In an animal cell, the plasma membrane keeps out unwanted objects. In a plant cell, the cell wall does this. Unwanted items would be any foreign unknown object, harmful bacteria, or wastes excreted by other cells. Cells only let in certain things, and they do this through selective permeability. They let in water and sugars and nutrients and other things that the cell requires. They can tell what to let in because proteins attached to the plasma membrane act as signalling devices, telling the plasma membrane whether or not to let something in. Some bacteria trick the plasma membrane into letting them in.

Answer 2

Some bad things not allowed into a cell include toxins, pathogens, and harmful substances that could potentially damage the cell's structure or interfere with its normal functions. Additionally, large molecules or foreign particles that could disrupt the cell's internal environment or block essential processes are also restricted from entering.