Water

Water constitutes two-thirds the mass of most organisms & 75% earth's surface.

Importance of Water to Life

1. Coolant: Has high heat of vaporization, aids body cooling.

2. High specific heat: ( H20 = 1 cal / g / degree C ) - bodies of water stay constant temp.

3. Transport: polarity - dissolves many substances.

4. Habitat: Major component of internal (organism) & external environments

[ Water is Highly Polar ]: shape, bond angle allow charge separation (Oxygen pulls electrons from Hydrogen, creating slight -2 charge at O end, slight +1 at each H.)

[Hydrogen bonding] - bond forming betweenthe positive pole of one water molecule and the negative pole of another. (The negative O momentarily "sticks" to a nearby positive H!)

Diagram of Hydrogen bonds (blue dashes) between 3 water molecules.

Properties of Water (Table 2.2 in book)

Property	Meaning	Importance of Property
1. Transparency	Light passes thru water.	Light reaches chloroplasts in cells & aquatic plants.
2. Universal Solvent	Many compounds dissolve in water.	Dissolved compounds can be brought to cells (via sap or blood) or move about cell cytoplasm.
3. Cohesion 4. Adhesion	Water molecules stick together due to H bonds. Water molecules stick to other molecules.	Small animals may walk on water. Capillary action. Water pulled to top of trees.
5. Heat Capacity	Large amounts of energy are needed to raise temp of water.	Water bodies have stable temperatures. Body temps can be maintained. Transfer of heat from warm to cool body parts.
6. High boiling point. 7. Density of Ice	Much energy needed to pull water molecules apart. Ice is less dense than water so it floats.	In nature, water rarely boils so life is spared. Ice insulates organisms living beneath.
8. Evaporation	Evaporation (boiling) requires much energy.	Evaporation can cool warm cells.

[See also the Shape of Water]

A waterstrider demonstrates how cohesion (H bonds) between water molecules allow it to move across water's surface.

Animations of Important Properties of Water:

Solvency of Water (how water dissolves ionic compounds) - Northland University

Hydrogen Bonds - Northland University

Polarity of Water Molecules: Formation of Ice - UC Davis

Slichter

Water

Water constitutes two-thirds the mass of most organisms & 75% earth's surface.

Importance of Water to Life

1. Coolant: Has high heat of vaporization, aids body cooling.

2. High specific heat: ( H20 = 1 cal / g / degree C ) - bodies of water stay constant temp.

3. Transport: polarity - dissolves many substances.

4. Habitat: Major component of internal (organism) & external environments

[ Water is Highly Polar ]: shape, bond angle allow charge separation (Oxygen pulls electrons from Hydrogen, creating slight -2 charge at O end, slight +1 at each H.)

[Hydrogen bonding] - bond forming betweenthe positive pole of one water molecule and the negative pole of another. (The negative O momentarily "sticks" to a nearby positive H!)

Properties of Water (Table 2.2 in book)

Property

Meaning

Importance of Property

1. Transparency

Light passes thru water.

Light reaches chloroplasts in cells & aquatic plants.

2. Universal Solvent

Many compounds dissolve in water.

Dissolved compounds can be brought to cells (via sap or blood) or move about cell cytoplasm.

3. Cohesion

4. Adhesion

Water molecules stick together due to H bonds.

Water molecules stick to other molecules.

Small animals may walk on water.

Capillary action. Water pulled to top of trees.

5. Heat Capacity

Large amounts of energy are needed to raise temp of water.

Water bodies have stable temperatures. Body temps can be maintained. Transfer of heat from warm to cool body parts.

6. High boiling point.

7. Density of Ice

Much energy needed to pull water molecules apart.

Ice is less dense than water so it floats.

In nature, water rarely boils so life is spared.

Ice insulates organisms living beneath.

8. Evaporation

Evaporation (boiling) requires much energy.

Evaporation can cool warm cells.