Water and Living Organisms

Learning Management System

Subject Name Biological Molecules

Topic Water and Living Organisms

Week 5

1. Chapter Overview The importance of Water and living organisms

2. Learning Objectives Know the importance of water in living organims Carry out laboratory work to identify the biological molecules

3. Learning Outcomes:On successful completion of this topic students should be able to:

Describe the importance of water for living organisms

Sate the properties of water which makes it importanf for life

Life Depends on Water

A. Water Is Liquid Due to Hydrogen Bonding1. Water is a polar molecule because of a slightly negative charge at the oxygen end

and a slightly positive charge at the hydrogen end.

2. Water molecules can form hydrogen bonds with each other.

3. Polar substances are hydrophilic (water loving); nonpolar ones are hydrophobic (water dreading) and are repelled by water.

B. Water Can Absorb and Hold Heat

1. Water tends to stabilize temperature because it has a high heat capacity – the ability to absorb considerable heat before its temperature changes.

2. This is an important property in evaporative and freezing processes.

C. Water Is the Biological Solvent

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1. The solvent properties of water are greatest with respect to polar molecules because “spheres of hydration” are formed around the solute (dissolved) molecules.

2. For example, the Na+ of salt attracts the negative end of water molecules while the Cl- attracts the positive end.

D. Properties of Water

PROPERTY COMPARISON WITH OTHER SUBSTANCES

IMPORTANCE IN THE OCEAN

Heat capacity & thermal conductivity

Highest of all liquids and solids except liquid ammonia

Prevents extreme temperature ranges encourages heat transfer

Latent heat of fusion Highest of all except ammonia Acts as a thermostat at freezing point

Latent heat of vaporization Highest of all substances Important in heat and water transfers to the atmosphere

Thermal expansionmaximum density is 4o C. for pure water, lower with increasing salinity

Allows fresher water near freezing to rise to surface, ice floats

Surface tension Highest of all liquids except mercury

Controls drop formation & behavior, cause of capillary waves

Dissolving powerDissolves more substances in greater quantities than any other liquid

Makes nutrients of all kinds available to organisms

Transparency Relatively greatMost transparent in visible range, thus allows underwater photosynthesis

Freezing & boiling point Much higher than similar substances

Allows most water to exist as a liquid

Related notes on water: Most water molecules are free, not locked in clusters. Clusters are very short lived (less than one-millionth of a microsecond). Water is less structured at higher temperatures.




At pressures over 1000 atmospheres all structure is lost, because structured regions are less dense. No structure is present in water vapor.

Temperature effects on water Adding heat to water raises its temperature within its current state. Adding heat to water existing at a state change boundary results in no temperature change, only the breaking of hydrogen bonds.

1.1. Other Properties of Water

Salinity Defined as the amount of salt in the water. Expressed as parts per thousand, written . Average salinity is 35 %°. Measured using electrical conductivity. Vapor pressure decreased by increased salinity. Increased salinity increases osmotic pressure.

Viscosity Defined as the resistance of a liquid to flow. Especially important to very small organisms near the surface. Viscosity increases with greater salinity and viscosity decreases with higher temperature. Different ions have different effects on viscosity.

Density Defined as mass per unit volume. Increasing salinity and/or pressure increases density. Increasing temperature decreases density.

KEY TERMS

KEY TERMS

1. Latent heat of fusion

2. Latent heat of vaporization

3. Surface tension

4. Viscosity




5. Density

REFERENCES

Cell and Molecular Biology Concepts and Experiments by Gerald Karp 2005, 3rd Ed., John Wiley & Sons,Inc.

Human Biology by Cecie Starr & Bevery McMillan 2007, 7th Ed., Thomson Brooks/Cole

Human Biology by Sylvia S. Mader 2004, 8th Ed., McGraw Hill



Water and Living Organisms

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