Cracking the AP Biology Exam


Cellular Energetics


In Chapter 2, we discussed some of the more important organic molecules. But what makes these molecules so important? Glucose, starch, and fat are all energy-rich. However, the energy is packed in the chemical bonds holding the molecules together. To carry out the processes necessary for life, cells must find a way to release the energy in these bonds when they need it and store it away when they don’t. The study of how cells accomplish this is called bioenergetics.

Generally, bioenergetics is the study of how energy from the sun is transformed into energy in living things.

All the energy for life comes from chemical bonds. During chemical reactions, such bonds are either broken or formed. This process involves energy, no matter in which direction we go.

Every chemical reaction involves a change in energy.

Energy is invested in the formation of bonds, whereas energy is released when bonds are broken. But even the breaking apart of chemical bonds requires the input of some energy. How, then, do cells manage to get the energy they need for life? In order for a chemical reaction to occur, the reacting molecules must get sufficient energy from enzymes.