CHAPTER 3: WATER AND LIFE
WHY WATER IS SO IMPORTANT TO LIVING ORGANISMS
One of the most important molecules for life
o The molecule that supports all life
Early life started in the water
Many cellular processes require water to occur
75% of earth ‘s surface is covered by water
Most cells are surrounded by water
POLAR COVALENT BONDS IN WATER MOLECULES
Results in hydrogen bonding
A water molecule is shaped like wide V
o Polar
o Overall charge is unevenly distributed
A water molecule can bond up to 4 other water molecules by hydrogen bonds
o This number can change when water is liquid since its molecules are always
moving
Polarity of the molecule and hydrogen bonding contribute to its behavior
o Oxygen is electronegative (likes to hold to electrons)
o Will grab onto more water molecules (via hydrogen bonds)
THE FOUR EMERGENT PROPERTIES OF WATER
Cohesion: Water that sticks to itself which is mostly due to Hydrogen bonds that
collectively help hold water molecules together.
o Contributes to the transport of water and dissolved nutrient against gravity in
plants
o Adhesion: Sticks to other things which is the attraction between different
substances
EX: a paper towel soaking up water
o Surface Tension: Measure of how difficult it is to stretch or break the surface of a
liquid which is the result of hydrogen bonds being tightly packed together and the
polarity of water
Allows water molecules to rest at the top of water which creates a strong
surface so that things can either float or sink
Moderation of temperature: Water can absorb or release relatively large amounts of heat
with only a slight change in its temperature. Reason being its hydrogen bonds
o Water changes temperature relatively slowly
o This requires a lot of energy in order to heat or cool down. This is because of the
difficulty of breaking hydrogen bonds
Heat must be absorbed to break hydrogen bonds
Heat is released when hydrogen bonds form
o Waters high specific heat
A measure of how well a substance resists changing its temperature when
it absorbs or releases heat
WHY WATER IS SO IMPORTANT TO LIVING ORGANISMS
One of the most important molecules for life
o The molecule that supports all life
Early life started in the water
Many cellular processes require water to occur
75% of earth ‘s surface is covered by water
Most cells are surrounded by water
POLAR COVALENT BONDS IN WATER MOLECULES
Results in hydrogen bonding
A water molecule is shaped like wide V
o Polar
o Overall charge is unevenly distributed
A water molecule can bond up to 4 other water molecules by hydrogen bonds
o This number can change when water is liquid since its molecules are always
moving
Polarity of the molecule and hydrogen bonding contribute to its behavior
o Oxygen is electronegative (likes to hold to electrons)
o Will grab onto more water molecules (via hydrogen bonds)
THE FOUR EMERGENT PROPERTIES OF WATER
Cohesion: Water that sticks to itself which is mostly due to Hydrogen bonds that
collectively help hold water molecules together.
o Contributes to the transport of water and dissolved nutrient against gravity in
plants
o Adhesion: Sticks to other things which is the attraction between different
substances
EX: a paper towel soaking up water
o Surface Tension: Measure of how difficult it is to stretch or break the surface of a
liquid which is the result of hydrogen bonds being tightly packed together and the
polarity of water
Allows water molecules to rest at the top of water which creates a strong
surface so that things can either float or sink
Moderation of temperature: Water can absorb or release relatively large amounts of heat
with only a slight change in its temperature. Reason being its hydrogen bonds
o Water changes temperature relatively slowly
o This requires a lot of energy in order to heat or cool down. This is because of the
difficulty of breaking hydrogen bonds
Heat must be absorbed to break hydrogen bonds
Heat is released when hydrogen bonds form
o Waters high specific heat
A measure of how well a substance resists changing its temperature when
it absorbs or releases heat
