![]() Energy-storing polymers like these are broken down into glucose to supply molecules of ATP. The sugar (glucose) is stored as starch or glycogen. Just as the dollar is used as currency to buy goods, cells use molecules of ATP as energy currency to perform immediate work. The synthesis of glucose is described by this equation (notice that it is the reverse of the previous equation): 6CO 2 + 6H 2O + energy → C 6H 12O 6 + 6O 2ĭuring the chemical reactions of photosynthesis, energy is provided in the form of a very high-energy molecule called ATP, or adenosine triphosphate, which is the primary energy currency of all cells. Because this process involves synthesizing a larger, energy storing molecule, it requires an input of energy to proceed. ![]() During photosynthesis, plants use the energy of sunlight to convert carbon dioxide gas (CO 2) into sugar molecules, like glucose (C 6H 12O 6). The breakdown of glucose, a simple sugar, is described by the equation: C 6H 12O 6 + 6O 2 → 6CO 2 + 6H 2O + energyĬarbohydrates that are consumed have their origins in photosynthesizing organisms like plants ( Figure 5.3). Living things consume sugar as a major energy source, because sugar molecules have a great deal of energy stored within their bonds. The metabolism of sugar (a simple carbohydrate) is a classic example of the many cellular processes that use and produce energy. Carnivores eat the herbivores, and decomposers digest plant and animal matter. 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. Using Light Energy to Make Organic Moleculesįigure 5.1 A hummingbird needs energy to maintain prolonged periods of flight.The Light-Dependent Reactions of Photosynthesis.Connections of Carbohydrates, Proteins, and Lipid Metabolic Pathways.Oxidation of Pyruvate and the Citric Acid Cycle.
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