![]() Plants use photosynthesis to capture sunlight, and herbivores eat those plants to obtain energy. All of the chemical reactions that take place inside cells, including those that use energy and those that release energy, are the cell’s metabolism.įigure 5.2 Most life forms on earth get their energy from the sun. Just as living things must continually consume food to replenish what has been used, cells must continually produce more energy to replenish that used by the many energy-requiring chemical reactions that constantly take place. Some of these chemical reactions are spontaneous and release energy, whereas others require energy to proceed. Cellular processes such as the building and breaking down of complex molecules occur through stepwise chemical reactions. Scientists use the term bioenergetics to discuss the concept of energy flow ( Figure 5.2) through living systems, such as cells. Cells must also export waste and toxins to stay healthy, and many cells must swim or move surrounding materials via the beating motion of cellular appendages like cilia and flagella. Pathogenic bacteria and viruses are ingested and broken down by cells. Additionally, signaling molecules such as hormones and neurotransmitters are transported between cells. Just as energy is required to both build and demolish a building, energy is required for both the synthesis and breakdown of molecules. Complex carbohydrates are broken down into simple sugars that the cell uses for energy. For example, the large proteins that make up muscles are actively built from smaller molecules. Nutrients and other molecules are imported, metabolized (broken down) and possibly synthesized into new molecules, modified if needed, transported around the cell, and may be distributed to the entire organism. ![]() In fact, the living cells of every organism constantly use energy. Energy is needed to perform heavy labor and exercise, but humans also use a great deal of energy while thinking, and even during sleep. Virtually every task performed by living organisms requires energy. The flight muscles in birds are extremely efficient in energy production.(credit: modification of work by Cory Zanker) Introduction The bird obtains its energy from taking in food and transforming the nutrients into energy through a series of biochemical reactions.
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