Cells use barriers to regulate their internal environments. Without their fatty barriers (membranes) cells wouldn’t function properly and we wouldn’t exist. Far from being static walls that prevent any movement or transport, these dynamic barriers enable cells to import and export the various materials they need to live.
Barriers enable cells to create specific internal and external environments
Membrane barriers come in a variety of flavors. Some cells have more membranes than others, their compositions are often different, and their structural properties vary quite a bit. Nonetheless, all cellular membranes are fat-based and selectively allow the transport of particular materials.
Indeed, membranes are good barriers because of their fatty composition. The internal and external environments surrounding cells are both water-based. Fat-based membranes largely repel the water-loving materials in these environments and thereby prevent them from crossing from one environment to the other in an unregulated way.
To obtain nutrients, grow, and function properly, cells selectively import and export materials from the external environment. They do so using proteins embedded in their membranes. A cell will produce more or less of a particular membrane protein depending on its needs. Below I describe how membranes and their embedded proteins enable some critical cellular functions.
Transmitting electrical signals
Nerve cells can transmit electrical signals because of the proteins embedded in their membranes. These proteins specifically import and export ions to build up electrical charge. By releasing this charge, nerve cells communicate with one another and coordinate bodily functions.
Detecting and eating dangerous invaders
Some of your immune cells have the ability to eat disease-causing pathogens. To do so, immune cell membranes attach to and surround the pathogens. Once eaten, the pathogens are destroyed.
Absorbing ingested water
The membranes of intestinal cells specifically transport salts from the gut into the body. Water follows the salt into the body through a chemical process called osmosis. The water can then enter the bloodstream and travel throughout the body. Without membrane-driven water uptake in the gut, we’d all be dead :D.
Overall, cellular barriers are incredibly useful because they permit certain materials to enter and exit. Far from dumb walls, evolution has honed these barriers into dynamic systems with a variety of functions. These functions enable us to do everything from think to eat cake. We wouldn’t exist without them.