Table of Contents
Energy Flow
All life on Earth is sustained by solar energy from the Sun. Photoautotrophs like plants use solar energy to fix carbon dioxide into carbohydrates. Heterotrophs obtain this energy when they either eat the plants or eat other animals that eat plants. Some of this energy is lost as heat in this system.
Laws of Thermodynamics
Thermodynamics is the study of the relationships that exist between energy, heat, work, and temperature. The laws of thermodynamics help us describe how the energy of a system changes and how it can be used within the system.
The first law of thermodynamics states that energy cannot be created or destroyed, but can be converted to different forms. This concept is called conservation. For example, photoautotrophs convert solar energy into chemical energy. Systems are not 100% efficient, so energy is lost from systems over time as thermal energy (heat).
The second law of thermodynamics states that everything is moving towards the lowest possible energy state and towards greater disorder (entropy). Energy is required to retain and maintain order, so higher entropy is associated with lower energy.
Types of Energy
Two categories of energy exist: kinetic energy and potential energy. Kinetic energy is associated with motion. Thermal energy (heat) is a form of kinetic energy because it is associated with the random movement of atoms or molecules. Potential energy is associated with the structure or location of a molecule. The chemical energy that is stored in bonds is a form of potential energy that is available for release during chemical reactions.
Chemical Reactions
Metabolism is the sum total of all the reactions in a cell or in an organism. Chemical reactions in organisms can either be exergonic or endergonic. Exergonic reactions occur spontaneously and release energy. Endergonic reactions are nonspontaneous and require an input of energy in order to proceed. Living things couple (or link) these reactions so they occur together. In this way, the energy released by the exergonic reaction can be used to fuel the endergonic reaction.
Catabolic reactions are those that break down large molecules into smaller ones. This process releases the chemical energy that was stored in the bonds. The released energy can then be used to perform anabolic reactions that build new molecules.
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