We inhale oxygen (O2) and exhale carbon dioxide (CO2), so it seems that we don’t need CO2 to survive. Since plants do the reverse – absorb carbon dioxide and expel oxygen – many think that plants don’t need oxygen to survive. Is this correct?
Plants can’t live without oxygen. They need it to (1) distribute minerals and nutrients to the entire plant; (2) to capture energy from sunlight in photosynthesis; and (3) to convert sunlight, water, and carbon dioxide into food such as carbohydrates, glucose, and cellulose.
At the same time, the answer is always more complex and interesting than it looks. Let’s dive in and look at some very curious details!
Both plants and animals breathe in, convert gases, and breathe them out either as oxygen (O2) or carbon dioxide (CO2). However, animal respiration uses lungs and bloodstreams while plant respiration is through stomata and cells. They also use oxygen in different ways.
Plants are all around us, so familiar, that we mostly take them for granted. Yet, many people have misconceptions about how plants breathe. Let’s clarify two words:
Transpiration is when: (1) roots absorb water from the soil, (2) water distributes minerals to stems and leaves, and (3) pores (stomata) of leaves diffuse water vapor and oxygen into the air.
Respiration is either (1) breathing or (2) using oxygen to release energy from food. In this article, we talk about this second meaning. The two (2) types of respiration are: aerobic (using oxygen to get energy from food) and anaerobic (getting energy from food without using oxygen).
FACTOID: Despite what you may have heard, plants do need oxygen for transpiration (to distribute minerals and nutrients to all the parts of the plant); for photosynthesis (to capture energy from light); and for food production (to convert light, water, and CO2 into starch, cellulose, and glucose).
Let’s do a quick review of how plants do all that with oxygen.
Plants get oxygen from water in the soil but, when that’s not enough, their leaves absorb oxygen from the air.
How do leaves do that exactly?
To protect them from drying out, nature has designed the outer “skin tissue” of plants so that water, carbon dioxide, and oxygen can’t go through. However, leaves have a ventilation system called stomata.
Stomata are tiny pores on the surfaces of leaves and stems (you’ll need a good microscope to see them) that can open, enlarge, shrink, or close to control how much water and gas a plant absorbs (inhales) or expels (exhales).
The oxygen that enters the stomata diffuses to the parts of the plant that lack oxygen. It’s only when there’s enough oxygen throughout the plant that cells begin to convert glucose into energy and the plant begins (or continues) to grow.
In other words, plants cannot grow very well when there’s a lack of oxygen. So, all you indoor gardeners, remember this: plants need carbon dioxide but they also need oxygen.
FACTOID: On average, there are 300 stomata on 1 square millimeter of a leaf. Some leaves have thousands of stomata per square inch.
How Plants Use Oxygen: Part 2 – Respiration & Photosynthesis
During growth spurts, plants need to absorb more oxygen than they produce. Lack of oxygen results in stunted growth and abnormal root structures.
Meanwhile, many are asking: plants produce oxygen during photosynthesis, so why do they need to absorb oxygen from the air? Can’t they just use the oxygen they produce?
Here’s the simplified answer:
Respiration: In respiration, plants convert food (such as glucose and carbohydrates) into energy to grow and develop roots, stems, branches, leaves, buds and so on. This process can only happen when there’s oxygen.
Photosynthesis: In photosynthesis, plants capture energy from light (the sun) and create food (sugars, starch) and expel the leftovers or extras (oxygen, water vapor). This entire process cannot happen when there’s no oxygen.
FACTOID: When plant photosynthesis is faster than respiration, they produce enough oxygen for them to use. However, when plants are growing fast, they need more oxygen than they produce. This is when the stomata on the surface of leaves begin to intake oxygen from the air.
Overall, however, plants produce more oxygen than they need, so don’t worry about plants sucking up the oxygen in your room while you’re sleeping. There’s no need to remove plants from a hospital room. In fact, plants can clean up indoor air as well as enrich it with oxygen.
How Plants Use Oxygen: Part 3 – Transpiration & Respiration
Plants breathe by transpiration as well as by respiration. These processes are different but both use oxygen. In other words, plants can’t breathe without oxygen.
Transpiration and respiration are separate processes that happen at the same time (they also sound almost the same). This might be why many confuse them. To clarify:
Transpiration is when water moves from the roots to the cells, stems, and leaves to distribute minerals and nutrients throughout the plant. Oxygen, which is necessary for water to form, is a critical part of transpiration.
Respiration is when plants absorb light (photosynthesis), and convert it with water, and carbon dioxide into food (like starch and glucose). The stomata (tiny pores) on leaves expel the extra, unneeded stuff (like water vapor and oxygen) into the air. Without oxygen, plants cannot respire.
FACTOID: Aerobic respiration is when cells use oxygen to release energy from food. Anaerobic respiration is when cells don’t use oxygen to release energy from food and instead use fermentation.
Nowadays, No plant can live without oxygen. In fact, all green plants, algae, moss, and almost all organisms on earth need oxygen. The exceptions are tiny, including microscopic animals in the deep sea, a parasite that lives in salmon, and some bacteria.
Aside from the E. coli bacteria that can live in both aerobic (with oxygen) or anaerobic (no oxygen) environments, there are also facultative anaerobes that thrive in oxygen as well as when there’s no oxygen. They grow by either anaerobic respiration or by fermentation.
While all plants need oxygen, some animals live in zero-oxygen environments. Here are some examples:
- Loricifera (Pliciloricus enigmatus): This is a microscopic sea animal that lives in the extremely salty, zero-oxygen environment of the Atalante Basin, about 3,500 feet under the Mediterranean Sea. Without its tapered mouth, it is less than one millimeter (160–268 µm) long.
- H. salminicola: This must be the only animal on earth that doesn’t need to breathe. This tiny parasite is about 10 millimeters long. It infects the muscle tissue of salmon in Oregon, Canada, Japan and Alaska. The parasite creates white, tapioca-like cysts.
- Archaea: These are a group of one-celled organisms that can theoretically turn metal into meat. Archaea live in extremely salty environments (halophiles); in extremely hot locations (thermophiles); or produce natural methane gas (methanogens).
- Clostridium: About 3-4 µm in size, they live in the air, soil, water, decaying plants, and sometimes in intestines of newborns as well as of healthy men and women. They’re called “anaerobes” because they don’t need oxygen to live. In fact, oxygen can kill them.
- Bacteroides: These microscopic pathogens (about 0.5 to 6.0 micrometers long) are helpful bacteria when they’re in the mouth, throat, or intestines; they protect against colitis. However, they cause inflammation and abscesses when they’re in anaerobic infections. They’re extremely resistant to many antibiotics.
Except for a few microscopic animals that live in extreme environments, all organisms on earth need oxygen. Plants, in particular, use oxygen in four ways:
- Photosynthesis: Plants use energy from light, along with nutrients and oxygen in the water to manufacture food such as sugars, cellulose, and carbohydrates.
- Transpiration: Plants use water (which has oxygen) to transport minerals and nutrients from the roots to all the parts of the plant.
- Respiration: Plants use oxygen in the water to convert food (glucose, starch) into energy. Afterward, the stomata expel the oxygen and water vapor into the air.
- Oxygen absorption: Plants can’t make food when it doesn’t have enough oxygen. When this happens, the stomata (the pores on leaf surfaces) absorb oxygen from the air. However, plants don’t suck out oxygen from your room at night. This is a myth. In fact, plants generally produce more oxygen than they need.
Is the oxygen that plants produce enough for them to live? Yes, it is, but only when plant photosynthesis is faster than its respiration. For example, when plants are growing fast, they produce more oxygen than they consume.
Is it true that plants convert carbon dioxide into oxygen? No. The oxygen that plants release into the air comes from the water that the roots take in.
Do plants absorb oxygen during photosynthesis? No. Plants release oxygen when plants photosynthesize during the day.
How well do plants clean indoor air? A study says that plants can remove almost 90% volatile organic compounds (VOCs) from indoor air, including cancer-causing chemicals such as formaldehyde and benzene. However, other sources say this is true only for laboratory conditions and not in actual homes and buildings.
Ant that’s it.
You’ve just completed a thorough review of how plants use oxygen. Now you can use this information for better indoor gardens. Congratulations!
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“Effects of Low-Oxygen Atmosphere on the Growth and Development of Arabidopsis Thaliana (L.) Heynh” by K. M. Ramonell, Louisiana State University (LSU Dissertations & Theses)
“The first metazoa living in permanently anoxic conditions” by R. Danovaro et al in BMC Biology
“Life without oxygen: what can and what cannot?” by A. J. Zehnder and B. H. Svensson in Experientia
“A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome” by D. Yahalomi, et al in PNAS
“Archaea: The Third Domain of Life” by T. Rowland in The Santa Barbara Independent
“Interior landscape plants for indoor air pollution abatement” by B. C. Wolverton, et a in Grow Real Food
“A Popular Benefit of Houseplants Is a Myth” by R. Meyer in The Atlantic
“Can Indoor Plants Really Purify the Air?” by M. Heid, in Time Magazine