What is required for plants to breathe?
Much goes on in a single breath. When we humans breathe, the body inhales oxygen through the lungs. The oxygen is then circulated to cells throughout the body via the bloodstream. At this point, the oxygen and glucose are converted to carbon dioxide and water, yielding energy, in a process called respiration or cellular respiration. The carbon dioxide is then returned to the lungs, where it is exhaled.
With plant life, things work a bit differently. They don’t breathe, per se, since they don’t use muscles to draw in air and have no bloodstream to distribute oxygen. Plants do, however, respire and they rely on their leaves to perform the exchange of oxygen and carbon dioxide.
More specifically, they rely on a series of tiny holes or pores found on the underside of the leaf. These holes are called the stomata (singular, stoma), and the number of stomata on a given leaf varies from plant to plant. In addition, plants also use their roots, stem, and to some extent, flowers to respire. Pores located on the branches of the plant are called lenticels.
Stomata work hard, pulling double duty as they also play a part in photosynthesis. Photosynthesis and respiration are complementary processes that use and make the same substances—water, glucose, oxygen, and carbon dioxide—but in different ways. Using carbon dioxide and water, photosynthesis creates oxygen and glucose. As mentioned above, this glucose is then combined with oxygen to produce carbon dioxide, water, and energy.
A key difference between the two processes is timing; respiration can occur at any time, while photosynthesis will only take place if there is sunlight. This is why, historically, people would refrain from putting plants in their bedroom; they feared the plants would steal the oxygen from the room (via respiration) and suffocate them during the night.
Thankfully, this isn’t true. Plants release much more oxygen through photosynthesis than they consume during respiration, so there is nothing to be concerned with there.
But back to the stomata. By opening and closing, the stomata not only control the intake of CO2 for glucose production, but also allow air to escape during photosynthesis and water and carbon dioxide during respiration. The opening and closing of these pores is regulated by cells known as guard cells. Guard cells are produced in pairs and shaped like quarter moons placed tip to tip with the dark space between them forming the stomatal pore.
Stomata are sensitive and easily affected by environmental conditions. Too hot and they stay open longer and in larger numbers. Too dry and they may close to help preserve moisture. When necessary, plants can control their stomata density by producing new leaves with fewer or greater numbers of pores commensurate with their immediate need.
So, to answer the original question, yes, our little green friends actually do breathe—but in their own way.
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