Study GuideBiology–Cellular Respiration1. Introduction to Cellular RespirationLiving things need energy to grow, repair themselves, and carry out daily activities. Someorganisms—especiallyplants—can capture energy directly from sunlight throughphotosynthesis.During this process, plants makeglucose, a type of carbohydrate that stores energy in its chemicalbonds.However, many organisms cannot perform photosynthesis.Animals, fungi, many protozoa, andmost bacteriadepend on plants (or on organisms that eat plants) for their energy. They obtain thisenergy by breaking down carbohydrates like glucose.1.1 How Cells Get Energy from FoodCells release the energy stored in carbohydrates through a process calledcellular respiration.During cellular respiration, glucose enters the cell’s cytoplasm and is gradually broken down througha series of chemical reactions.The energy released is not usually used right away. Instead, it is stored in a special molecule calledadenosine triphosphate (ATP). ATP is made by combiningadenosine diphosphate (ADP)with aphosphate group. You can think of ATP like arechargeable battery—it stores energy and releases itwhenever the cell needs power for activities such as movement, growth, or making new molecules.1.2 The Role of Oxygen and Carbon DioxideCellular respiration producescarbon dioxide (CO₂)as a waste product. This carbon dioxide isreleased into the environment, where plants can reuse it during photosynthesis to make moreglucose.Oxygen (O₂)is also essential for cellular respiration. It acts as the finalelectron acceptor, allowingthe process to continue efficiently. This oxygen is the same gas that plants release duringphotosynthesis.Because of this exchange,photosynthesis and cellular respiration are closely connected.Photosynthesis stores energy from sunlight in glucose, and cellular respiration releases that energyso cells can use it.Preview Mode
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