The processes that support living organisms revolve around an intricate combination of exchanges on the cellular level. These exchanges known as photosynthesis and cellular respiration individually and collectively support the process called life by producing energy. Careful examination of the activities occurring at the cellular level in these processes reveals a kind of “subset” of tasks that explain the methodical order of events necessary to sustain a living organism. Understanding the relationships between metabolism, entropy, equilibrium, Adenosine Triphosphate (ATP), NADPH, chlorophyll, chloroplasts, electrons, carbon, glucose, and energy is critical to the comprehension of the processes that feed life.
Energy is observed in many forms such as light, heat, electricity, or motion which are interchangeable. However, the term energy actually refers to “anything that can do work” (Pruitt, pg. 276, 2006.) An interesting feature of energy is that the total amount of energy that exists remains the same even when the form of energy changes. For example, “X” amount of light energy would equal “X” amount of heat energy. The concepts that explain this phenomenon are known as the law of thermodynamics. The first law describes that the amount of available energy in the world is always the same regardless of its form, and even if it changes form the total remains the same. The second law states that shifts in energy always occur in a manner that distributes the energy from a narrow focus to a broader focus. Consider the example of a narrow light beam as focused or highly organized. Now compare it to a broad light beam where the light energy is disorderly, or widely dispersed. If left to its own devices, energy will naturally shift from the organized to the disorderly. This demonstrates the concepts of entropy and equilibrium, where entropy represents the amount of disorder in the world, and equilibrium is the point when entropy reaches its maximum point (Pruitt, 2006.) So how do these facts, relate to the relevance of energy?
Living organisms need energy to complete the tasks necessary to sustain life. Chemical reactions occurring at the cellular level produce energy for the cell to capture, a process known as metabolism (Pruitt, 2006.) An example of the metabolic process occurring in all cells is the production of Adenosine Triphosphate, or ATP which is a compound containing phosphorus atoms. These atoms have negative electrons that repel from one another producing energy used by the cell to break down carbon into glucose. Glucose is the sugar carbon used by cells for food. The breakdown process occurs over the course of several metabolic changes, the last of which causes the reproduction of ATP. This self-renewing activity, combined with the fact that ATP exists in every type of cell makes ATP a useful form of energy currency. Since all metabolic pathways use, produce, and breakdown ATP to create energy, use energy to complete biological work, and maintain constant levels of Adenosine exchanging ATP as currency among the cells occurs without confusion (Pruitt, 2006.) Let’s consider the ways these reactions occur in a particular organism.
Organisms such as plants or bacteria use photosynthesis, a chemical process that uses the energy from light to convert carbon dioxide into a food source, known as glucose. Plant cells contain organelles known as chloroplasts. The chloroplasts contain a green pigment called chlorophyll. In this light dependent process, the chlorophyll reacts to the light, carbon dioxide (Co2), and water, charging the electrons. Hydrogen in the water reacts converting the Co2, ATP, and NADPH to glucose. When light is not available, the same process occurs with the addition of a protein known as Rubisco. This addition of this protein produces the same chemical reaction that occurs when light is available. This process is called light-independent reaction and is commonly