Remember the levels of organization of life?

Life: Small Picture to Big Picture

Atoms

• The most abundant elements in living organisms are:

Carbon (C)

Hydrogen (H)

Oxygen (O)

Nitrogen (N)

Why is life carbon-based?• Carbon can bond and form

stable compounds with a large number of atoms.– Carbon can bond with 4

atoms – Nitrogen can bond with 3

atoms– Oxygen can bond with 2

atoms– Hydrogen can bond with 1

atom

• Silicon can also bond with 4 atoms, but compounds are not as stable.

Abundance of Elements in Life

The 4 most common elements found in living things:

Carbon, Hydrogen, Oxygen, Nitrogen

The 5th and 6th most common:

Phosphorus and Sulfur

HO

C

NS & P

Notice the amount of H and O?

Properties of Water

Molecular Structure of Water

Polarity of Water

These partial charges are very important to the biochemistry of living things. (Polar things stick to polar things, nonpolar things stick to nonpolar things.)

How Soap WorksSoap is made up of molecules that have both a polar and nonpolar side. The polar side is attracted to polar water molecules, the nonpolar side is attracted to nonpolar grease or oil molecules. The soap ends up surrounding the grease with its nonpolar tails all the way around. The polar heads facing the outside are attracted to water molecules and wash the surrounded grease or oil away.

Hydrogen Bonding

• The partial charges of the oxygens and hydrogens between water molecules attract each other.

• The resulting bond is very weak. It’s called a hydrogen bond.

• H-bonds are very important in Biology.

H-bond

Hydrogen-Bonding

Hydrogen Bonding

Cohesion & Surface Tension

H-bonds are the reason water forms drops, and can hold up a water strider.

Cohesion & Surface Tension

• Cohesion: the attraction between water molecules due to H-bonds. This results in water’s ability to form drops, instead of staying in separated droplets.

• Surface Tension: This is also a result of cohesion. The combined strength of all the H-bonds between water molecules in a pool causes a film or surface that is slightly resistant, sticky, and supportive.

Adhesion

• The partial charges on water molecules can also form H-bonds with other molecules. Usually these molecules are also polar, or charged.

                                             

Capillary Action

• Plants and trees are able to get water to their branches and leaves from their roots using capillary action.

• Capillary action is an effect caused by the combination of both cohesion & adhesion.

Specific Heat of Water

• Water has a high specific heat capacity.

• It takes a lot more heat energy to increase the temperature of water by 1 C than it does for alcohol or iron!

• This is why organisms can stay out in the hot or cold for a duration of time. Water helps to regulate and stabilize body temperature.

Water Trivia• What percentage of your body is water?• A: Your body contains as much as 60% water.

Men have more water in their bodies than women, because women have more body fat.

• What percentage of the Earth’s surface is water?

• A: Water covers about 70% of the Earth. 98% of that water is found in the oceans.

Water Trivia

• Is it possible to die from drinking too much water?

• A: Yes. Too much water causes all of your body’s cells and tissues to swell. Fluid can flow into your lungs, you will act intoxicated, and eventually may suffer seizures and die. “Water intoxication” is more likely to occur if you drink a lot of water in a short period of time.