Cellular Processes.

http://en.wikipedia.org/wiki/Cell_(biology)

Growth and Metabolism.

Between successive cell divisions, cells grow through the functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions: catabolism, in which the cell breaks down complex molecules to produce energy and reducing power, andanabolism, in which the cell uses energy and reducing power to construct complex molecules and perform other biological functions. Complex sugars consumed by the organism can be broken down into a less chemically complex sugar molecule called glucose. Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP), a form of energy, through two different pathways.

The first pathway, glycolysis, requires no oxygen and is referred to as anaerobic metabolism. Each reaction produces ATP and NADH, which are used in cellular functions, as well as two pyruvate molecules that derived from the original glucose molecule. In prokaryotes, all energy is produced by glycolysis.

The second pathway, called the Krebs cycle or citric acid cycle, is performed only by eukaryotes and involves further breakdown of the pyruvate produced in glycolysis. It occurs inside the mitochondria and generates much more energy than glycolysis, mostly through oxidative phosphorylation.