Water

I. Why is water important to organisms. A I. Why is water important to organisms? A. Water is the universal solvent. In organisms it can transport many substances by dissolving them.

How does dissolving work? The slight charges on water molecules allow them to pull apart the atoms that make up the solute. ----------------------------------------------- Ex: Watch the animation of how water dissolves salt!

C. Most organisms consist of 70-95% water. B. Most chemical reactions in organisms require water. C. Most organisms consist of 70-95% water.

II. Properties of Water A. Water is a polar molecule. Polar means that water molecules have a positive end and a negative end.

Diagram of a Water Molecule *Each hydrogen is held to the oxygen by a covalent bond.

B. Water resists temperature change. C. Water expands as it freezes B. Water resists temperature change. C. Water expands as it freezes. Therefore, ice is _________ dense than water. Watch the animation of water as it freezes!

D. adhesion—water molecule’s attraction for other substances Ex: creation of a meniscus E. capillary action (related to adhesion) Ex: plant taking up water through its stem

Capillary Action (Vascular Tubes from Mahogany Tree)

F. cohesion—water molecules’ strong attraction for each other. Two waters are held together by a hydrogen bond.

G. Unique properties that are the direct result of cohesion: 1. high surface tension Ex: bug “skating” across a pond 2. high heat of vaporization—takes a high temperature to turn water to steam

Surface Tension (Water Strider)