What is Osmoregulation?
[[File:2618_Nephron_Secretion_Reabsorption.jpg|thumb|Human osmoregulation in the nephron]] '''Osmoregulation''' is how living things keep the right amount of [[salt]] and water in their bodies. All living things do this, from [[bacteria]] to humans. The basic idea is that organisms keep [[osmotic pressure]] by controlling their water and salt concentrations. There are regulators and conformers. Conformers match their environment, and regulators do things which act to keep their internal water at a standard level of saltiness. Sea fish, for example, tend to gain salt if they live in seawater. So they actively put out ([[excrete]]) salt from their [[gill]]s. River fish, on the other hand, take the salt out before they excrete water. Some fish, like the [[flounder]], live in both fresh and salt water at different stages in its life. They adapt to whichever water they are in. == Plants == All plants regulate their water balance. [[Xerophyte]]s like [[Cactus|cacti]] keep water inside so they do not become too salty. Plants that live in seasonal wetlands also have ways of avoiding [[desiccation]]. Many plant leaves have a waterproof [[cuticle]] to regulate the loss of water, and use [[spiracle]]s for gas exchange. Osmoregulation is an important aspect of [[homeostasis]]. it involves the balance between water and [[Solution|solute]] contents of [[cell]]s. == Land animals == The change from being in water to living on land was one of the most significant things which happened in evolution.<ref>Carroll, Robert 2009. ''The rise of amphibians: 365 million years of evolution''. Johns Hopkins. {{ISBN|978-0-8018-9140-3}}</ref> From the perspective of water balance this was one of the most dramatic changes ever made. Suddenly, the new land animal had the problem of losing too much water through its skin, and taking in too little if it moved away from the water. === Kidneys === [[Kidneys]] are the organ of osmoregulation in [[vertebrate]]s, including humans. In the [[nephron]], blood is filtered through the [[glomerulus]].