Question

Why does salt thrown on a frog's body kill it?

Answer 1

Osmosis is the movement of water from an area of high water concentration to an area of lower water concentration. As mammals, the outer layer of our skin contains a large amount of keratin. This keratin (found in highest concentration in the dead cells at the skin's surface) forms a water tight barrier stopping osmosis from occurring between our bodies and the outside world. The keratin keeps our body's water in (notice that the blood circulates to the layer just below the epidermis) and the environment's water out (we can jump in the swimming pool and we don't come out with our cells full of pool water). Unlike the skin of mammals, the skin of amphibians contains no keratin layer and indeed the skin of amphibians has evolved a role in water and gas exchange. The salt you place on that poor helpless frog has a very low water concentration (if the concentration of water gets high enough the salt will dissolve in the water. in this case osmosis will move water in the direction of higher salt concentration, another way of saying "in the direction of lower water concentration." ) Osmosis moves water out of the frog into the salt layer thus dehydrating the frog's cells killing the animal.

Answer 2

Thank you for your explanation. I was aware of the osmosis link but the keratin difference is new to me. I asked another question about potato strips in a salt solution and I know the change in size is related to osmosis as well. However, I don't think the colour change is osmosis related. I read on another site that that there is a reaction between the starch in the potato and the iodine in the salt. Would you know, by chance?