The Need For Energy - All organisms need energy to stay alive. They use this energy to grow, maintain body processes, and reproduce. Many kinds of organisms require energy to move, as well. Energy to support these activities is released in the bodies of organisms from carbohydrates and other energy-rich organic molecules.
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| The Need For Energy |
In animals, plants, and most other species (kinds) of organisms, the process that releases this energy is cellular respiration. (For a small number of species that live in environments without oxygen, the energy-releasing process is fermentation.) The word equation and chemical equation below summarize the process of cellular respiration.
How is energy stored in energy-rich molecules in the fi rst place? It is stored through the process of photosynthesis. Through photosynthesis, plants, algae, and some kinds of bacteria use the Sun’s light energy to chemically convert carbon into carbohydrates such as sugars and starches. The word equation and chemical equation below summarize the process of photosynthesis.
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| Cellular respiration and Photosynthesis |
Organisms that are able to use the Sun’s energy to produce food for themselves in this way are called producers. Producers are also known as autotrophs, which means “self-feeders.”
The ruby-throated hummingbird and other animals are not able to make the energy-rich molecules they need to fuel their life processes. Instead, they must obtain these molecules by consuming other organisms (or absorbing nutrients from them). Thus, animals and some other kinds of organisms are heterotrophs, which means “other-feeders.” Heterotrophs that consume other heterotrophs or autotrophs are called consumers.
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