K is for potassium. Potassium is element 19 on the periodic table and its symbol arises from Latin for potassium carbonate kalium. (Sodium metal, symbol Na comes from Latin for sodium carbonate natrium.) It has an atomic mass of 39.098 g/mol. It is an alkali metal and is therefore known for its explosive reaction with water. It is actually more reactive than sodium metal and results in pretty purple flames. The K 40 isotope (sorry, I can't seem to publish superscript so this is not the correct notation) is actually radioactive-that's right that banana you had on your Cheerios this morning was radioactive! Of course this is nothing to be concerned about since this stuff is everywhere and is postulated (by Isaac Asimov) to be a contributing factor to our evolution. Please note that only one hundredth of one percent of potassium atoms in the world are actually the radioactive K 40 (which can be figured out by examining the atomic mass; however, since I started this blog for my sister I should probably skip the math lesson.)
But what I would like to talk about today is K+, the potassium ion. This little guy is very important to life. For plants it is essential for growth, which is why it is included in plant fertilizers. My research has so far has found that the exact role of potassium in plant growth has yet to be defined. It is associated with the movement of water, nutrients, and carbohydrates within the plant, all of these things tied inextricably to plant growth. Research has shown that potassium improves the efficiency of water use in the plant, therefore it is tied to plant stomata, which are the pores through which plants "breathe". It has been found to increase plants' resistance to disease and insects. It also results in early growth, increased production of proteins, and winter-hardy plants (important for Canadian crops).
In animals, K+ is way cooler. It is involved in nerve transmission through out the body. Animal cell membranes have a Na+/K+ pump: this is the primary transporter on cell membranes. What happens is that the transporter pumps three ions of Na+ outside the cell, and then pumps two ions of K+ inside the cell. This results in a potential energy gradient across the cell membrane. When a nerve impulse is sent, it converts this potential energy into kinetic energy by allowing the ions to flow back down the gradient. (In other words, opposite to the process that established the gradient). When you are low on K+, then the gradient cannot be established, which means that no nerve signals can be sent, and your muscles, usually starting with your fingers, will start to freeze up. Now think about the most important muscle in your body. Hopefully you are thinking of your heart. Imagine what would happen if your heart muscle was low on potassium. It would freeze. This would result in death. So if you start to dip in K+ a great way to get some is by eating a banana. Bananas are very rich in potassium.
References:
Gray, T. The Elements 2009, Black Dog & Leventhal Publishers Inc. New York, NY.
Pratt, C. W.; Cornely, K. Essential Biochemistry 2004, Wiley & Sons Inc. Danvers, MA.
Petrucci, R. H.; Harwood, W. S.; Herring, F. G. General Chemistry 8th ed. 2002, Prentice Hall Inc. Upper Saddle River, NJ.
Potassium for Crop Production www.extension.umn.edu/distribution/cropsystems/dc6794.html accessed 11/14/2010.
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