Introduction to Energy and Metabolism

What you’ll learn to do: Discuss energy and metabolism in living things

Scientists use the term bioenergetics to describe the concept of energy flow (Figure 1) through living systems, such as cells. Cellular processes such as the building and breaking down of complex molecules occur through stepwise chemical reactions. Some of these chemical reactions are spontaneous and release energy, whereas others require energy to proceed.

This diagram shows energy from the sun being transferred to producers, such as plants. The producers in turn transfer energy to consumers and decomposers. Animals also transfer energy to decomposers.

Figure 1. Ultimately, most life forms get their energy from the sun. Plants use photosynthesis to capture sunlight, and herbivores eat the plants to obtain energy. Carnivores eat the herbivores, and eventual decomposition of plant and animal material contributes to the nutrient pool.

Just as living things must continually consume food to replenish their energy supplies, cells must continually produce more energy to replenish that used by the many energy-requiring chemical reactions that constantly take place. Together, all of the chemical reactions that take place inside cells, including those that consume or generate energy, are referred to as the cell’s metabolism.

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