BIOL 1020 ZHONG
Chapter 3: Water and Life
Overview: Life as we know it requires water. All organisms that we know of are made mostly of liquid water, and most of their metabolism requires an aqueous medium. In addition, many organisms live in liquid water or in an environment dominated by water in its various states (solid, liquid, or gas). Some numbers: cells are typically 70% or more water by mass about 75% of the Earth’s surface is covered by liquid water
But then, just being common on the Earth doesn’t make something essential for life. A large percentage of the Earth’s crust is sand, but we don’t consider sand a requirement for life. What is it about water that makes it so special?
I. Water molecules are polar nature.
A. oxygen atoms are electron seeking (electronegative), especially compared to hydrogen; thus for an oxygen-hydrogen bond:
B. The polar character of water allows water molecules to form many (up to 4) hydrogen bonds.
II. What properties of water are important for life?
A. Cohesion of water molecules
1. Cohesion:
e.g.:
2. Adhesion:
e.g.:
3. Surface tension:
B. Ability to moderate temperature
1. The unusual specific heat of water leads to temperature stability specific heat –
High specific heat of water à temp. stability
2.
3. Evaporative cooling
Heat of vaporization:
C. Expansion upon freezing
1. Freezes at 0 degrees Celsius – ice
2.
3.
4.
D. Versatility as a solvent
1. Solution -
2. Solute -
3. Solvent –
The highly polar character of water makes it an excellent solvent for other polar substances!
4. Hydrophilic substances –.
5. Hydrophobic substances –.
III. Acids and Bases
A. An acid is any substance that increases the H+ concentration of a solution.
B. Acids are proton donors
1. An acid is a substance that dissociates in solution to yield hydrogen ions (H+)
2. H+ = one proton
C. A base is any substance that reduces the H+ concentration of a solution
D. Bases are proton acceptors
E.
Overview: Life as we know it requires water. All organisms that we know of are made mostly of liquid water, and most of their metabolism requires an aqueous medium. In addition, many organisms live in liquid water or in an environment dominated by water in its various states (solid, liquid, or gas). Some numbers: cells are typically 70% or more water by mass about 75% of the Earth’s surface is covered by liquid water
But then, just being common on the Earth doesn’t make something essential for life. A large percentage of the Earth’s crust is sand, but we don’t consider sand a requirement for life. What is it about water that makes it so special?
I. Water molecules are polar nature.
A. oxygen atoms are electron seeking (electronegative), especially compared to hydrogen; thus for an oxygen-hydrogen bond:
B. The polar character of water allows water molecules to form many (up to 4) hydrogen bonds.
II. What properties of water are important for life?
A. Cohesion of water molecules
1. Cohesion:
e.g.:
2. Adhesion:
e.g.:
3. Surface tension:
B. Ability to moderate temperature
1. The unusual specific heat of water leads to temperature stability specific heat –
High specific heat of water à temp. stability
2.
3. Evaporative cooling
Heat of vaporization:
C. Expansion upon freezing
1. Freezes at 0 degrees Celsius – ice
2.
3.
4.
D. Versatility as a solvent
1. Solution -
2. Solute -
3. Solvent –
The highly polar character of water makes it an excellent solvent for other polar substances!
4. Hydrophilic substances –.
5. Hydrophobic substances –.
III. Acids and Bases
A. An acid is any substance that increases the H+ concentration of a solution.
B. Acids are proton donors
1. An acid is a substance that dissociates in solution to yield hydrogen ions (H+)
2. H+ = one proton
C. A base is any substance that reduces the H+ concentration of a solution
D. Bases are proton acceptors
E.