METABOLISM
Metabolism is such a big word to explain a simple idea. We all need energy to survive. Plants, animals, or bacteria, we all need energy. Energy doesn't just float around in a form we can use to survive. We need to eat (mainly sugars) and digest food. That process of chemical digestion and its related reactions is called metabolism. Metabolism is the total of all of the chemical reactions an organism needs to survive.

Sounds a lot like biology. Why's it here in biochemistry? Two main chemical processes make our world go round. There are two simple chemical reactions. The first is called glycolysis. That's the breakdown of sugars. The second process is called photosynthesis. That is the reaction that builds sugars. You need to remember that the overall metabolism of an organism includes thousands of chemical reactions. Glycolysis and photosynthesis are the cornerstones to life.

BUILDING UP
First, you need to build up the molecules that store energy. We'll start with photosynthesis. It's no use explaining the breakdown of sugars without telling you how they were made.

LIGHT (Energy) + CO2 + H2O --> C6H12O6 + O2

This is the reaction that only plants can do (and some algae/bacteria). They take sunlight and combine carbon dioxide (CO2) and water (H2O). They create Glucose (C6H12O6) and oxygen gas (O2). Remember, plants put the energy in glucose.

BREAKING DOWN
It's metabolism and the process of glycolysis that takes that energy out of the sugar related molecules.

C6H12O6 + O2--> Usable Energy (ATP) + CO2 + H2O

Cells then use that extra energy to power the functions of the cell. The energy isn't still floating around; it's stored in an excitable compound called adenosine triphosphate (ATP). ATP is the power molecule used all over organisms and their cells to power the secondary reactions that keep us alive.