How does the cell membrane work?

The cell membrane is selectively permeable which means it facilitates the entry and exit of substances. This regulation of movement across the cell membrane can be done by diffusion, endocytosis, exocytosis, or through channels and transporters. Passive transport through the cell membrane occurs by diffusion which does not require the input of cellular energy. Transmembrane protein channels and transporters located within the cell membrane function on both sides of a membrane to transport molecules across it. Endocytosis is a process in which cells internalize particles by engulfing them. Alternatively, exocytosis removes waste by discharging contents outside of the cell.