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All organisms need energy to survive, grow, and reproduce. Energy is produced through an organism’s metabolism. Metabolism is the term used to describe all the chemical reactions that an organism needs to maintain life, like converting food or sunlight into energy. This energy is used for a variety of different purposes such as reproduction, movement, maintaining homeostasis, and essentially all other aspects of life. Excess energy, above what is needed to run all the necessary processes, typically results in energy storage (in fats or carbohydrates) or growth of an organism. Without enough energy, an organism will not be able to complete all the functions of life and will ultimately die. However, not all organisms have the same energy requirements or use energy in the same way.
Energy Use
Maintaining a body temperature that is neither too high nor too low is essential for life. As discussed in Unit 3, moving outside of these temperature bounds can have irreversible negative impacts such as mutations, protein denaturation, or death. Organisms use different strategies to regulate body temperature and metabolism. Endotherms use thermal energy generated by metabolism to maintain a relatively constant body temperature. Mammals and birds are both endotherms. Ectotherms do not have the same ways of maintaining body temperature. Instead, they use their environment to help them regulate. They may move into the sun or gather with other organisms to increase their temperature or move to the shade to decrease their temperature. Reptiles and insects are two examples of ectotherms. With these organisms, they are often sluggish in cold temperatures and must wait for the environment to warm them up before they can be more active.
Another way organisms regulate energy usage is through changing their reproductive approach. Asexual reproduction, when there is only one parent, doesn’t require the same amount of energy as sexual reproduction, when there are two parents. This is because there is no mating, courting, or production of gametes. Some organisms have the ability to switch between these two reproduction strategies depending on environmental conditions and resource availability.
The size of an organism, or body mass, typically dictates metabolic rate. A small organism generally has a higher metabolic rate than a larger organism. This is because small organisms have a larger surface area relative to their volume. This higher surface area to volume ratio means that they lose heat more quickly to their environment and, for endotherms, means they must use more energy to maintain a constant body temperature. As a result, they need more energy relative to their body mass in order to live.
