Let’s imagine the following:
We’re stranded on a deserted island. We need to drink, otherwise we’d become dehydrated, but we can’t find any fresh water. Would it be a good idea to drink seawater to survive?
The quick answer is no. Want to know why? I’ll explain it in this article.
About Our Cell Membranes
To understand why drinking this water isn’t a good idea, it’s vital to know how the membrane of our (eukaryotic) cells works.
It’s super important to understand that our cell membrane is semipermeable, also known as selectively permeable.
What does this mean? It means that it only allows solvent molecules (like water) to pass through it. This phenomenon is called osmosis.
About Seawater
We all know a key characteristic of seawater: its high salt content. It’s important to understand that seawater contains a much higher level of salt (almost four times more) than the fluids in our bodies.
Explanation of the Phenomenon
Knowing how our cell membranes work and the main characteristic of seawater (its high salt concentration), we can explain the phenomenon by which we become dehydrated when drinking seawater.
By drinking seawater, we increase the osmotic pressure of our bodily fluids, making them saltier than our cells.
As such, our cells always try to equalize their internal osmotic pressure with the external environment. With a higher salt concentration outside, the cells release a large amount of water to balance that pressure.
This release of water causes our cells to shrink, resulting in an appearance like the one shown below.
Over time, the cells would dehydrate, leading to their death. So yes, drinking only seawater on a deserted island would kill us.
