Water and Life Chapter 3 Overview: The Molecule That Supports All of Life Water is the biological medium on Earth All living organisms require water more than any other substance Most cells are surrounded by water, and cells themselves are about 70?95% water The abundance of water is the main reason the Earth is habitable ? 2011 Pearson Education, Inc. Figure 3.1 Polar covalent bonds in water molecules result in hydrogen bonding The water molecule is a polar molecule: the opposite ends have opposite charges Polarity allows water molecules to form hydrogen bonds with each other ? 2011 Pearson Education, Inc. Figure 3.2 Hydrogen bond Polar covalent bonds ? ? ? + ? + ? ? ? ? ? + ? + ? ? Four emergent properties of water contribute to Earth?s suitability for life