Water and Fitness of Environment - Introduction to Biology - Lecture Slides, Slides of Biology

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Chapter 3:

Water and the

Fitness of the

Environment

H

O Bent Geometry

Methane: Replace C with O and 2xH with 2 x Electron Pairs and you have Water!

O

H

H

H

H

H

H

C

Hydrophilic/Hydrophobic

 Hydrophilic = Water Loving

• These are things that like to dissolve in or be wet by water
• Typically these things have polar bonds or full charges  Hydrophobic = Water Hating
• Things that do not like to dissolve in or be wet by water
• Typically these things lack polar bonds or full charges
• For example, hydrocarbons are hydrophobic, e.g., oils

Cohesion

“Cohesion” refers to the high potential for water molecules to hydrogen bond to each other

High Heat Vaporization

Water resists evaporating (i.e., vaporizing) because hydrogen bonds must be broken in order for water to transition from the liquid to the gas state

Evaporative Cooling

Faster (hotter) molecules leave the liquid-phase first, lowering the temperature of the remaining liquid—you (via your sweat and skin) and engineers take advantage of this by using water evaporation to cool things

Water Adheres to Water

To optimize the exchange of oxygen and carbon dioxide between the body and the environment, the lung is divided into alveoli, or small air sacs, that maximize the area over which gas is in close contact with capillary blood. A thin layer of water coats each of the alveoli and protects the living tissue underneath. This creates an extensive air- water interface within the lung cavity, and the surface tension of the water tends to collapse the lungs. Surface tension accounts for approximately two-thirds of the contractile force within the lungs. The effect of surface tension is greater for structures with tighter curvature, and consequently alveoli that lack surfactant tend to collapse at the end of exhalation. The subsequent tearing open of the alveoli upon inhalation damages the epithelium of the distal airways, resulting in impaired lungs that exchange gas poorly.

H

O Liquid at Room Temp 2

Formula Mol.Weight Phys. State CO 2 44 Gas O 2 32 Gas CO 28 Gas N 2 28 Gas H 2 O 18 Liquid CH 4 16 Gas H 2 2 Gas

Water is a liquid at room temperature not because of its mass because of hydrogen bonding (cohesion)

Solution Lore

 Water dissolves substances to which it can readily hydrogen bond (or is otherwise attracted to typically because the substance contains full or partial charges)  Solute = a substance that dissolves in another substance  Solvent = the substance the solute dissolves in  Solution = a solvent in which solutes are dissolved  Aqueous solution = a solution in which water is the solvent

pH Buffering

Carbonic-Acid-Bicarbonate Buffering (e.g., of blood)

pH = less H 3 O +^ ≈ H +