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The Sound of Science - "Don't Drink the Salt Water"

K: I’m Kate Powers from NIU STEM Outreach, with Jeremy Benson and this is the Sound of Science on WNIJ.

J: Kate, I have a question from Ariana, it sounds like she may have been reading Swiss Family Robinson or watching Cast Away. Ariana wants to know why you can’t drink sea water as a source of hydration?

K: Great question. If you were really thirsty, you might think salt water could be a last resort to get water into your body. But drinking salt water actually dehydrates you. Let me be clear: Drinking salt is deadly. To understand more, cast your mind back to biology class and think about osmosis.

J: Osmosis? That is when particles pass through a membrane of some sort, right?

K: Exactly -- Osmosis is all about balancing concentrations. If you have a semipermeable membrane separating two water solutions, one solution 10% salt and the other solution with 0% salt, the salt ions will slowly pass through the membrane until the concentration of both solutions is the same, or 5% in this case.

J: Okay, I get that. But where is there a semi permeable membrane in our body?

K: Every cell in our body has one! If the cells encounter a solution that is saltier than the cell, the cell’s membrane will try to even out the concentration. Too much salt destroys the cells, eventually causing death!

J: Yikes! But we eat salt all the time, why is salt water so dangerous?

K: Well, your body is designed to flush your system of too much salt. Normally that is completed by drinking plenty of water which flushes the salt out in urine. But our body is only capable of producing urine with a 2% concentration of salt. Sea water has a 3% concentration of salt. Without extra fresh water, our bodies are incapable of peeing away the salt, which will eventually destroy the body’s cells.

J: Wow – that’s an intense chain of events. But the ocean is full of creatures, how do they survive in salt water?

K: It depends on the creature. Most ocean mammals have a higher salt concentration in their bodies than humans. So, the salt water isn’t very salty to them.

J: That’s pretty cool. I hope I’m never lost at sea without fresh water. Keep your questions coming to stemoutreach@niu.edu. This is The Sound of Science on WNIJ.

K: Where you learn something new every day.  

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