Most cells get their energy from cellular respiration, a process that breaks down glucose molecules and harvests the chemical energy they contain. This essay ...
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Mitochondria are often referred to as the powerhouses of the cell. These important organelles transform glucose, a simple sugar, into molecules of an energy-rich substance called ATP. In a multistep process called cellular respiration, mitochondria can convert a single molecule of glucose into as many as 38 molecules of ATP. This conversion of one large molecule into many smaller molecules allows cells to parcel out the energy they take in. A tiny biochemical reaction that requires only a tiny amount of energy can thus be powered by just a few molecules of ATP without wasting the energy of an entire glucose molecule. Indeed, ATP drives virtually every cellular process that takes place in your body -- from the smallest to the largest. Although ATP is critical to the survival and functioning of every cell, different types of cells have dramatically different energy requirements. Just as the activity levels of workers in, say, a bakery vary from person to person, depending on each worker's specific job and on the time of day, the activity levels of your body's cells vary from one type of cell to another. Compare a living cell from the outer layer of your skin with a cell from a muscle in your arm, for example. While both types of cells serve important functions, your outermost skin cells, which serve mostly a protective role, perform very little active work. Muscle cells, in contrast, are often required to contract relentlessly. In return, muscle cells and other highly active cells, including nerve and liver cells, demand huge amounts of ATP.