Water and the Fitness of the Environment

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Slide 1

The Molecule That Supports All of Life

Water is the biological medium on Earth

All living organisms require water more than any other substance

Most cells are surrounded by water, and cells themselves are about 70–95% water

The abundance of water is the main reason the Earth is habitable

Slide 2

Fig. 3-1

Slide 3

Concept 3.1: The polarity of water molecules results in hydrogen bonding

The water molecule is a polar molecule: The opposite ends have opposite charges

Polarity allows water molecules to form hydrogen bonds with each other

Animation: Water Structure

Slide 4

Fig. 3-2

Hydrogen

bond

 –

H

 +

H

O

——

——

 +

 +

 +

 –

 –

 –

Slide 5

Fig. 3-UN1

Slide 6

Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for life

Four of water’s properties that facilitate an environment for life are:

Cohesive behavior

Ability to moderate temperature

Expansion upon freezing

Versatility as a solvent

Slide 7

Cohesion

Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion

Cohesion helps the transport of water against gravity in plants

Adhesion is an attraction between different substances, for example, between water and plant cell walls

Animation: Water Transport

Slide 8

Fig. 3-3

Water-conducting

cells

Adhesion

Cohesion

150 µm

Direction

of water

movement

Slide 9

Surface tension is a measure of how hard it is to break the surface of a liquid

Surface tension is related to cohesion

Slide 10

Fig. 3-4

Slide 11

Moderation of Temperature

Water absorbs heat from warmer air and releases stored heat to cooler air

Water can absorb or release a large amount of heat with only a slight change in its own temperature

Slide 12