Cells and Harmful Substances 

The plasma membrane is selectively permeable, which means it allows some substances to enter and leave the cell unrestricted while others are restricted.

Some toxins in the extracellular fluid cross the plasma membrane of bacteria unrestricted, interfering with normal chemical reactions, and ultimately killing the affected cell.

Why are cells unable to stop the flood of these harmful substances into the cell?

cells
Why are cells unable to stop the flood of these harmful substances into the cell? - 5 interesting facts to note 2