Murfreesboro is a city in Pike County, Arkansas, United States. The population was 1,764 at the 2000 census. The city is the county seat of Pike County. Crater of Diamonds State Park is located just to the south. The crater is an eroded lamproite pipe where diamonds were discovered in 1906. 100,000 were found by 1933, and visitors to the park may still take away whatever they can find.
The guard cells surround each stoma in a plant cell. They regulate  the opening and closing of stomata to facilitate gas exchange and  control transpiration in plants.
Plants can lose a lot of water via evaporation through the stomata, and open stomata also provide pathogens with a means for entering the plant. Two cells border each stoma (which is just a tiny hole in the leaf). These cells are called guard cells. Guard cells use turgor pressure to regulate the opening of stomata. When the plant wants to open its stomata, the guard cells take up ions (mostly K+ and Cl-) and sugars through ion channels and pumps. Because the solute concentration is now high inside the guard cells, water moves in and the cells expand. This expansion causes the guard cells to expand and puff out, opening the pore.