From Seed to Seed:
Plant Science for K-8 Educators
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From Seed to Seed: |
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F. Respiration Do plants really breathe?When animals breathe, they use their lungs and diaphragm to draw in air. The lungs use this air to provide oxygen to the blood. The waste air, containing carbon dioxide, is exhaled. Is this the same thing as respiration? Although you often see the words "respiration" and "breathing" used interchangeably, technically speaking, respiration takes place on a cellular level. Respiration is the act of breaking the chemical bonds in food substances, releasing the energy contained within these bonds. We often hear talk about how many calories we've "burned" during a workout at the gym. This burning is actually cellular respiration-we're breaking the chemical bonds in stored food and using the energy released to run on that treadmill! (We also use the energy for all other body functions, such as digesting food, producing new cells, or even thinking.) And as with other types of burning, oxygen is required for the process. The chemical equation for cellular respiration is: (CH2O) + O2 --> CO2 + H2O + energyLook closely at this equation and you'll see that it is essentially the equation for photosynthesis in reverse!  The reactants, carbohydrates and oxygen, yield carbon dioxide, water, and energy as products. This process takes place over four distinct stages. In the first stage, glycolysis, the carbohydrate glucose (general formula CH2O) is broken down into two smaller molecules. These smaller molecules are called pyruvic acid or pyruvate. In the Krebs cycle, the second stage, these pyruvate molecules are further broken down into carbon dioxide. The electrons that result from the formation of carbon dioxide are passed on to the third stage, the electron transport chain. As the electrons move through the electron transport chain, energy is released. This energy is used to create ATP (adenosine triphosphate) during oxidative phosphorylation, the final stage. ATP is the source of energy for plant functions. The entire process takes place in the mitochondria. Back to our original question: Do plants breathe? Plants don't use muscles
to draw in air-the exchange of gases is passive. So, technically, plants
don't breathe. But plants do respire. Like animals,
they use oxygen in the process of breaking down carbohydrates, and use
the energy released for basic metabolic functions such as repairing and
replacing tissues, and building complex molecules like proteins and oils.
During respiration, plants, like us, release carbon dioxide and water
vapor. |
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