CHAPTER 2: Water and Life
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Water and Life
–Life on Earth began in water and evolved there for 3 billion years.
•Modern life still remains tied to water.
•Your cells are composed of ….
–The abundance of water is a major reason Earth is habitable.
•Like no other common substance, water exists in nature in all
three physical states:
The Structure of a Water Molecule
•What atoms make up a water molecule?
•How are these atoms joined together to make a water molecule?
•What type of bond joins the atoms together?
•In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen
The Properties of Water
•Atoms in a molecule that form covalent bonds may share electrons equally, creating a
____________________________________
•If electrons are shared _________________________________________ molecule is created
Water’s polarity leads to hydrogen bonding and other unusual properties
•The charged regions on water molecules are attracted to the ….
–This attraction forms weak bonds called ________________________________
Essential Question
•How does water rise from the roots of a redwood tree to the very top?
The Cohesion of Water
–Water molecules stick together as a result of hydrogen bonding.
•This is called cohesion.
•Due to cohesion water molecules form a …
•Cohesion is vital for water transport in plants.
The Adhesion of Water
–Water molecules stick to other polar (charged) molecules by hydrogen bonding
•This is called adhesion.
•Due to adhesion __________________________________________________________ of
the conducting tubes keeping the column of water from falling due to gravity
•Cohesion is vital for water transport in plants.
Cohesion and Adhesion in Your Life
•Can you think of an example of cohesion and adhesion in your everyday life?
•Explain how these properties of water explain this example.
Water’s Life-Supporting Properties
–The polarity of water molecules and the hydrogen bonding that results explain most of
water’s life-supporting properties:
•Water’s …
•Water’s …
•Floating …
•Versatility of water …
Essential Question
•How do insects walk on water?
Surface Tension
Surface tension is the measure of how difficult it is to stretch or ...
•Hydrogen bonds give water an unusually high surface tension.
•It is as if a film is formed on the surface of the water and this allows insects to walk on the
surface
Surface Tension in Your Life
•What is an example of surface tension in your life?
Essential Question
•Why do people sweat and some animals pant to reduce their body temperature
How Water Moderates Temperature
•It takes a lot of __________________________________________________ hydrogen bonds
–Therefore water is able to absorb a great deal of heat energy without a large increase in
temperature
–As water cools, a slight drop in temperature releases a large amount of heat
–Because of hydrogen bonding, water has a strong resistance to temperature change.
–A water molecule takes a large amount of energy with it when it evaporates
–This leads to ____________________________________________
–That is why people sweat and some animals pant
Essential Question
•Why does ice float rather than sink?
•How would life in a lake be affected if ice sank and lakes froze from the bottom up?
The Biological Significance of Ice Floating
•Due to hydrogen bonds molecules in ice are…
–The density of ice is lower than liquid water.
•This is why …
–Since ice floats, ponds, lakes, and even the oceans do not freeze solid.
–How would life in a lake be affected if ice sank and lakes froze from the bottom up?
Water as the Solvent of Life
–A solution is a liquid consisting of two or more substances evenly mixed.
•The dissolving agent is called the _______________________
•The dissolved substance is called the __________________________
Water as the Solvent of Life
•Solutes whose charges or polarity allow them to stick to water molecules
dissolve in water
–They form aqueous solutions
Essential Question
•Why is your blood mostly water?
•Why is the inside and outside of your cells mostly water?
Acids, Bases, and pH
- Acid
•A chemical compound that donates H+ ions to solutions.
- Base
•A compound that accepts H+ ions and removes them from solution.
- To describe the acidity of a solution, we use the pH scale.
–Cells are kept close to pH 7 by ____________________
–Buffers are substances that __________________________ change.
•They accept H+ ions when they are in excess.
•They donate H+ ions when they are depleted.
–Buffering is not foolproof.
•Example: acid precipitation
Acid precipitation threatens the environment
•Some ecosystems are threatened by ___________________________________
•Acid precipitation is formed when air pollutants from burning fossil fuels combine with water
vapor in the air to form sulfuric and nitric acids
–These acids can kill fish, damage buildings, and injure trees