Biology Chapter 3

• • Cohesion and adhesion
• • Ability to buffer temperature changes
• • Less dense as a solid than a liquid
• • It is the solvent in our cells
•      – Cells are 70-95% water
•      – Life evolved in water

• The oxygen has a polar covalent bonds with the hydrogens

• – Oxygen is delta-
• – Hydrogen is delta+

• Water molecules are held together by hydrogen bonds

– The attraction of water molecules for each other is the reason for its special properties

• • Cohesion
• – Water molecules stick to each other
• – Allows for surface tension of water
• • Adhesion
• – Water molecules stick to other substances(other than water)
• • Why?
• – Hydrogen bonds between water molecules

• • Can absorb and store heat
• • Can release heat
•          – Heat=total amount of kinetic energy (energy of motion)in a body of matter
• • Why?
•          – Heat is used to break the hydrogen bonds first
•          – THEN, the heat increases molecular movement (which increases the temperature)

• • Benefits for life
•         – Moderates ocean temperature
•         – Moderates cellular temperature
•         – Moderates coastal climates

• • 0 C is the temperature that liquid water becomes ice
•      – Each water is hydrogen bonded to 4 other water molecules
•      – The bonding arrangement prevents compaction
•     – Therefore, ice is 10% less dense than liquid water

• • Benefits
•     – Frozen water is on the surface of lake’s etc. in winter
•     – The surface is exposed to the sun’s heat and thaws in later seasons
•      – If it sunk, bodies of water would permanently freeze

– Substances that are attracted to and can be dissolved in water

– Polar and ionic substances

– Substances that avoid water and therefore cannot be dissolved in water

– Non-polar substances

• Water ionizes such that the molar concentration of H+ is 10-7 mole/liter

– Mole= 6.02 x 1023 molecules

– 1 molar solution = 6.022 x 1023 molecules/L

• • pH = -log10 [H+]
• – Note it is a logarithmic scale so each pH unit is a 10 fold difference in hydrogen ion concentration.

• • Neutral pH is 7
• – Example water

• • Acidic pH is less than 7
• – Acids increase [H+]    Example: HCl

• • Basic pH is more than 7
• – Bases decrease [H+] Example: NaOH

• Buffers- a substance that act as reservoirs for H+

• – Minimize pH change–
• -Accepts or donates hydrogen ions
• • If pH increases it donates H+
• • If pH decreases it accepts H+

• H+ and 0H- are very reactive, so natural buffers areused in cells

– Cells are very sensitive to pH changes• Common buffers used in biology experiments

– Tris, MOPS, sodium phosphate