Water in biology .........................

Water

1. WATER AND ITS ROL IN BIOLOGY

2. The number of electrons required to complete an atom’s valence shell generally determines how many covalent bonds that atom will form.

3. Polar bond

4. Hydrogen bond

5. The extraordinary qualities of water emerge in large part from the hydrogen bonding that organizes water molecules into a higher level of structural order.

6. C ohesive behavior

7. Related to cohesion is surface tension, a measure of how difficult it is to stretch or break the surface of a liquid. The hy- drogen bonds in water give it an unusually high surface tension .

8. Water has a high specific heat: Heat is absorbed when hydrogen bonds break and is released when hydrogen bonds form. This helps keep temperatures relatively steady, within limits that permit life.

9. Because the crystal is spacious, ice has fewer molecules than an equal volume of liquid water. In other words, ice is less dense than liquid water. Floating ice becomes a barrier that protects the liquid water below from the colder air.

10. V ersatility as a solvent.

11. Occasionally, a hydrogen atom participating in a hydrogen bond between two water molecules shifts from one molecule to the other .

12. A buffer is a substance that minimizes changes in the concentrations of H+ and OH− in a solution. It does so by accepting hydrogen ions from the solution when they are in excess and donating hydrogen ions to the solution when they have been depleted.

13. References Biology in Focus. Second Edition. Lisa A. Hurry [et al], (2013). “Chemistry and cells”p. 19-34. Pearson Education.