olism sometime in their life, but few know what it really means. The metabolism of a living organism is composed of all of the chemical reactions that occur in the organism. Some of the reactions that occur in the organism are described as anabolic, meaning that they take simple molecules and build more complex molecules out of them, while other reactions are catabolic, where large, complex molecules are broken down into simple ones. You were introduced to the idea of a chemical reaction in the first lab exercise, and also to the idea that it is food that we eat that ultimately supplies the energy that is needed to fuel all of the metabolic processes going on in the organism. That energy ultimately came from sunlight that was packaged by plants through photosynthesis into molecules that can be ultimately used in cellular respiration. Later in the semester, you will spend more time learning about energy and both of these processes.A living organism is built from a variety of organic molecules. These molecules include nucleic acids, proteins, carbohydrates, and lipids. The nucleic acids include DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid). DNA is the molecule that carries the genetic information for each cell, while RNA is the molecule that is the intermediary between the DNA and proteins. You will learn more about these molecules in another exercise. This exercise will focus on the proteins, carbohydrates and lipids that are found in the foods that we eat.Let’s get back to that PB&J sandwich. How is it that you can get the molecules necessary to sustain life from it? First, each of the components of the sandwich is made of molecules that were produced through a variety of anabolic reactions, including photosynthesis. Your body, through the digestion process, has the ability to break down or catabolize these larger, more complex molecules (polymers) back into their component monomers that can then be completely dismantled to release energy (through respiration) or reconstructed through other anabolic reactions to build new cells. In the next section, you will gain some background about each of these different molecule types, and then look at how your digestion process liberates these molecules from the foods you eat.