Bio H - Biochem
Properties of Water
In addition to Carbon, living things must depend heavily on the presence of water to maintain their survival. We all
know that living things need water to live, but can you actually list some reasons why?
Functions of water in the body:
Function:
Acts as a solvent
Provides cushioning
Acts as a medium for
chemical reactions
Acts as a lubricant
Helps materials be
transported
Regulates temperature
Participates in hydrolysis
Example of where/how:
Maintains moisture
Needed for sense organs
to function
But why water? What is so special about this little, tiny, inorganic molecule that allows it to do all this? Basically it is all
in the unique chemistry of H2O. Let’s start with the basics. Remember those covalent and ionic bonds? Turns out a very
special type of covalent bond holds the 2H’s to the O in water. It’s called a Polar covalent bond.
What is different about a polar covalent bond and the nonpolar covalent
bond that carbon loves to make?
What does this do to the molecule that is formed by the polar covalent bond?
Compounds that are made with polar covalent bonds can therefore be attracted to other polar covalent compounds OR
even ionic substances because of the partial charges of the substances. These attractions are called hydrogen bonds.
Bio H - Biochem
If the hydrogen bonds are forming between a water molecule and another
water molecule it is called Cohesion. (water sticking to water) Where do
we see cohesion?
If the hydrogen bonds are forming between a water molecule and a
different polar or ionic substance it is called adhesion. (water sticking to
other stuff) Where does adhesion come up in biology?
Both of the above make water an excellent solvent. This means it is GREAT at dissolving other things, solutes, making it
very useful in the body. All the materials that need to travel about the body and into our cells need to be dissolved.
Water is so good at dissolving that it is known as the universal solvent. BUT only other polar substances and ionic
substances can dissolve in water. Nonpolar substance cannot. To make a nonpolar substance dissolve, you need a
nonpolar solvent.
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How does the chemical structure of water make it such a good solvent? (for a solvent to dissolve a solute, what has
to happen to the molecules?)
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Name a nonpolar substance that is important in the body.
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When talking about solubility, there is a phrase “like dissolves like.” Considering what you read above, what does
this mean?
Water is often involved in mixtures of all types. A mixture is anything that combines two or more things in the same
space WITHOUT chemically altering them. In other words, our substances are just occupying the same space, they
haven’t formed bonds. Mixtures fall into one of three categories listed below. Describe each so you know the
difference. (include some examples that you can identify with!)
Homogeneous solutions:
Heterogeneous suspensions:
Colloids:
Finally water requires a very large amount of energy to change its temperature. This is referred to as the specific heat of
a substance. Why would this be beneficial to living things here on Earth?