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? Though
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 those 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 like other
types of burning, oxygen is required for the process.
The chemical equation for cellular respiration is:
(CH2O) + O2
CO2 + H2O + energy
Carbohydrates plus oxygen yield carbon dioxide plus water
plus energy.
Look closely at this equation and you’ll see that
it’s essentially the equation for photosynthesis in reverse!
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.
Plants only photosynthesize in the presence of light, but
they are continuously respiring, day and night. Even so, overall they release much
more oxygen during photosynthesis than they consume during respiration!
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