# Water --- **Water** is, simply put, *the* most important [[molecule]] on Earth. Not only is it just everywhere, but it is absolutely essential for [[biology|life]] as we know it. The chemical formula is $H_2O$. Two hydrogen atoms form [[covalent bond|covalent bonds]] with a single oxygen atom. The oxygen has a much higher [[electronegativity]] than the hydrogen, which makes it a [[polar and nonpolar|polar]] molecule. ![[partial charge.png]] ## Special Properties Has many special properties that make it so important. Here are some in no particular order: Water is **the universal [[solution|solvent]]**. It is *incredibly* good at dissolving other other [[polar and nonpolar|polar]] molecules. Water has a **high surface tension** due to it's ability to form many [[hydrogen bond|hydrogen bonds]]. One this is useful is that it allows water being brought so far up a [[plants|tree]]. Water is **more dense as a liquid than as a solid**. Ice floats, which means glaciers float in the ocean, which insulates it and prevents catastrophic surface level fluctuations (for now). Water **holds a lot of heat**. This insulates plant roots in the winter time, and is also what makes [[sweat glands|sweating]] such an effective cooling process. ## Water in Biology Water is the single most important molecule in [[biology]]. All biology comes from water. All of biology is dissolved in water. It's either surrounded by water or it's filled by water. It's useful for it's ability to form [[hydrogen bond|hydrogen bonds]], [[hydrolysis and condensation reactions|dehydration reaction]]. Water serves these general functions in our bodies: transportaion, lubrication, cushioning and excreting wastes. It also allows [[osmosis]], a force that is possible due to water's ability to pass through semi-permial plasma membranes. ___