Water and the Fitness of the Environment

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3

Ice

Hydrogen bonds are stable

Slide 20

Fig. 3-6a

Hydrogen

bond

Liquid water

Hydrogen bonds break and re-form

Ice

Hydrogen bonds are stable

Slide 21

The Solvent of Life

A solution is a liquid that is a homogeneous mixture of substances

A solvent is the dissolving agent of a solution

The solute is the substance that is dissolved

An aqueous solution is one in which water is the solvent

Slide 22

Water is a versatile solvent due to its polarity, which allows it to form hydrogen bonds easily

When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules called a hydration shell

Slide 23

Fig. 3-7

Cl–

Na

Cl–

+

+

+

+

+

+

+

+

–

–

–

–

–

–

–

–

Na

+

–

–

–

+

Slide 24

Water can also dissolve compounds made of nonionic polar molecules

Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions

Slide 25

Fig. 3-8

(a) Lysozyme molecule in a

nonaqueous environment

(b) Lysozyme molecule (purple) in an aqueous

environment

(c) Ionic and polar regions

on the protein’s surface

attract water molecules.

Slide 26

Fig. 3-8ab

(b) Lysozyme molecule (purple) in an aqueous

environment

(a) Lysozyme molecule in a

nonaqueous environment

Slide 27

Fig. 3-8bc

(c) Ionic and polar regions

on the protein’s surface

attract water molecules.

(b) Lysozyme molecule (purple) in an aqueous

environment

Slide 28

Hydrophilic and Hydrophobic Substances

A hydrophilic substance is one that has an affinity for water

A hydrophobic substance is one that does not have an affinity for water

Oil molecules are hydrophobic because they have relatively nonpolar bonds

A colloid is a stable suspension of fine particles in a liquid

Slide 29

Solute Concentration in Aqueous Solutions

Most biochemical reactions occur in water