Does plants need oxygen

How many trees does it take to produce oxygen for one person?

Asked by: Aaron Hacon, Norwich


Trees release oxygen when they use energy from sunlight to make glucose from carbon dioxide and water. Like all plants, trees also use oxygen when they split glucose back down to release energy to power their metabolisms. Averaged over a 24-hour period, they produce more oxygen than they use up; otherwise there would be no net gain in growth.

It takes six molecules of CO2 to produce one molecule of glucose by photosynthesis, and six molecules of oxygen are released as a by-product. A glucose molecule contains six carbon atoms, so that’s a net gain of one molecule of oxygen for every atom of carbon added to the tree. A mature sycamore tree might be around 12m tall and weigh two tonnes, including the roots and leaves. If it grows by five per cent each year, it will produce around 100kg of wood, of which 38kg will be carbon. Allowing for the relative molecular weights of oxygen and carbon, this equates to 100kg of oxygen per tree per year.

A human breathes about 9.5 tonnes of air in a year, but oxygen only makes up about 23 per cent of that air, by mass, and we only extract a little over a third of the oxygen from each breath. That works out to a total of about 740kg of oxygen per year. Which is, very roughly, seven or eight trees’ worth.


  • Do London plane trees actually absorb pollution into their bark?
  • When trees grow, where does the matter come from?
  • How do trees grow straight up, even on a slope?
  • Why have trees evolved such a variety of leaf shapes?

Oxygen: Grass vs Trees Name: Mike Grade: N/A Location: N/A Country: N/A Date: N/A Question: Given the replacement of some native forested areas (East Texas) by intensively farmed facilities (year round farming) is grass going to produce more oxygen per unit area of land than the trees removed?
Replies: The following may be helpful.
Anthony Brach Ph.D.
and thanks for the question.
Does grass produce more oxygen than trees? I think yes and no.
A field of grass might generate more mass of grass in a year than the equivalent addition of mass in a similar area of forest. It would depend a geat deal on the specific species of grass and forest plants you are trying to compare.
What is more important in the long run is the NETT production of oxygen. Oxygen is being produced and used up at the same time. What we need to consider is the overall change. Do we produce more than we use up ( a NETT GAIN) , or do we use up more than we produce? (A NETT LOSS)
In order to see a NETT production of oxygen, we must also see a NETT production of carbon products – noticibly wood. Wood represents the locking up of the Carbon extracted from CO2 in order to release oxygen. So forests produce lots of wood, they must also produce lots of oxygen – which is true. Grass on the other hand produces no wood. Its carbon is turned into carbon products such as sugars, starches and cellulose. These are all good carbon products, and represent a production of oxygen, and they are all produced by the forest plants as well. The problem is in the next step – what happens to the grass? If it is left on the ground it rots, and uses up oxygen as the sugars and starches and cellulose rot and release CO2 again. By equivalence, the forest may lose all its leaves in fall.
If the grass is eaten by a cow, then the cow uses oxygen to ‘burn’ the grass as fuel, and produces CO2. Similarly, parts of the forest plants are eaten – fruits berries leaves etc.
Either way, the NETT production of oxygen in a field of grass is very small, because the carbon products are not as long lasting as wood is.
This locking up of carbon is a hot topic at the moment, with terms like carbon banks and carbon sequestering and carbon trading. By locking carbon up, either in living forests or as underground reserves of CO2, we are helping to reduce CO2 in the atmosphere, and hopefully reducing the greenhouse effect which is helping to drive global warming. Industries which produce a lot of CO2 by burning coal and oil etc, can offset their emissions by investing in the planting of carbon bank forests. The effectiveness of this strategy is debated though. To offset the emissions resulting from the production and burning of 1 gallon of ethanol (biofuel) you would have to grow approximately 10 pounds of timber – (not including leaves etc.) To make the offset effective, you have to grow 10 pounds of WOOD for EVERY gallon of ethanol. That’s a 5000 lb tree for every car every year. If you keep using petrol or gasoline, the tree has to be even bigger!
Nigel Skelton
Tennant Creek

How Plants Acquire Their Energy

Plants must get food into their systems in order to acquire energy and continue living, similar to animals. Plants create energy for animals to use, so they must replenish their nutrients. And plants breathe, in a way. They take in the carbon dioxide that all the animals give off, and they give off oxygen for all the animals to use. Pretty cool design, isn’t it?

Making energy from the ultimate energy source

Photosynthesis is the process by which plants convert energy from the sun. It is the process that allows plants to create organic molecules that they use as fuel. Here is how it works.

  • The molecules of chlorophyll contained in the chloroplasts absorb energy in the form of light from the sun. Some plants need more sunlight than others, but all need at least a little.

  • Instead of taking in oxygen and breathing out carbon dioxide like animals do, plants take in carbon dioxide from the atmosphere. Plants absorb water from the ground up through their roots.

    During photosynthesis, the energy from the sun splits the water molecules into hydrogen and oxygen. The oxygen molecules are given off by the plant and emitted into the atmosphere. Molecules of ATP are created within the plant cell. These reactions are called photochemical or light reactions because they require light to occur.

  • Enzymes within the plant then catalyze the combination of hydrogen and carbon dioxide to create a carbon compound that is called an intermediate. An intermediate is a compound used to continue a process to create a different compound.

    In plants, the intermediate is called phosphoglyceraldehyde (PGAL). PGAL goes on in the process to produce glucose, which the plant uses as fuel to survive. These reactions are called carbon-fixation reactions (or dark reactions to differentiate them from the light reactions above) because atoms of carbon are “fixed”; that is, they are put into stable compounds that can be used purposefully instead of just floating around the cell aimlessly.

  • When the plant has created more glucose than it needs to sustain life, it combines glucose molecules into larger carbohydrate molecules called starch. The starch molecules are stored within the large vacuoles in the plant cells. When necessary, the plant can break the starch molecules down to retrieve glucose for energy or to create other compounds, such as proteins, nucleic acids, or fats.

Flowin’ through the xylem and phloem

Plants undergo photosynthesis to produce energy for themselves (and ultimately humans). Light and water are needed to perform this process. But, how do the plants get the water and light into their cells?

Tissues called the xylem and the phloem usually are found together in what are called vascular bundles. Both types of tissue conduct substances up through the root and stem of a plant. The xylem conducts water and minerals from the soil; the phloem “flows” sugar molecules.

All plant cells have a cell wall, but cells in the xylem have an additional cell wall to give them extra strength (helps to avoid a blowout of water through the stem). Vessel elements are specialized cells in the xylem that form columns called vessels. Water passes through holes at the ends of each vessel element, and continues up through the entire vessel column.

Phloem tissue contains cells called sieve-tube elements, which connect in columns called sieve tubes. Each sieve-tube element has a pore on the end of it, through which the cytoplasm from one sieve-tube element can “touch” the cytoplasm of the next sieve-tube element. This structure allows the fuel that the plant makes in the leaves to pass through and nourish the rest of the plant. This process is called translocation.

Transporting water from cell to cell

Plants have two ways of moving water from outside the root toward the inside of the root to the xylem and phloem tissue. Water can flow between the cell walls of adjacent cells. Think of this area as a hallway. Or water can flow between cells through tubes connecting the cytoplasm of each cell, much like people can walk through doors of adjoining rooms.

The inspiration for transpiration

Transpiration is the technical term for the evaporation of water from plants. As water evaporates from the leaves (or any part of the plant exposed to air), it creates a tension in the leaves and tissues of the xylem. Because plants lose water through openings in the leaves called stomata, they must regain water. Therefore, the inspiration for transpiration is the loss of water. The loss of the medium that carries necessary minerals inspires the plant to pull more water in from the ground.

Where do plants obtain the oxygen necessary to utilize foods?

Like most organisms, prokaryotes require carbon and energy to create nutrients such as carbohydrates, proteins, lipids, and nucleic acids. Prokaryotes obtain carbon and energy from a variety of sources. Certain prokaryotes use carbon dioxide as their carbon source. Called autotrophs, these prokaryotes derive energy from different sources, such as photosynthesis or inorganic molecules. Photoautotrophs, including the cyanobacteria and the green sulfur and purple sulfur archaebacteria, derive their energy from light. Chemoautotrophs, such as the soil bacteria Nitrobacter and Nitrosomonas, derive their energy from inorganic compounds such as hydrogen sulfide, ammonia, and iron. Heterotrophs are organisms that rely on ready-made organic compounds such as glucose or alcohol for their carbon source. Heterotrophs obtain energy by degrading organic molecules, such as plant or animal matter. A small group of bacteria, the photoheterotrophs, use light as their energy source, while chemoheterotrophs use organic compounds for both their carbon and energy sources.

The Oxygen Machine

Photo Credit:


To understand that human beings (as well as other animals) perform the respiration process because we need air to breathe and because oxygen is ultimately the fuel that allows our cells to produce energy from the food we eat.


The main focus of this lesson is to review the basics of respiration (breathing) and to teach students the importance of oxygen to the human body. To burn food for the release of energy stored in it, oxygen must be supplied to cells, and carbon dioxide removed. Lungs take in oxygen for the combustion of food and they eliminate the carbon dioxide produced. It is also important to point out to the students that a lack of oxygen or breathing pure oxygen is detrimental to our health. Another focal point of this lesson is that respiration is fundamental for our health and overall fitness. In fact, our bodies can use oxygen more efficiently if we exercise and eat properly.

By the end of elementary school, students should know that by breathing, people take in the oxygen they need to live. This basic knowledge allows middle-school students to develop a more sophisticated understanding of how respiration works in terms of basic macroscopic (e.g., major organs involved) and microscopic (e.g., cellular) processes involved with breathing.

By the end of middle school, students should know that to burn food for the release of energy stored in it, oxygen must be supplied to cells and carbon dioxide removed. They should understand the following macroscopic and microscopic processes: lungs take in oxygen for the combustion of food and they eliminate the carbon dioxide produced; the urinary system disposes of dissolved waste molecules; the intestinal tract removes solid wastes; the skin and lungs rid the body of heat energy; and the circulatory system moves all these substances to or from cells where they are needed or produced, responding to changing demands.

When students take biology in high school, they will receive instruction in the process of cellular respiration (glycolysis, Krebs cycle, electron transport chain, etc.) that will fill in the details of exactly how glucose from food is broken down to yield energy, or ATP, so it is not necessary that students have this detailed understanding at the middle-school level. It would be best if this lesson could come after a discussion of the circulatory system.

Research shows that students up to the age of seven have little knowledge about the human organism; however, by age nine or ten, students have a marked increase in their knowledge. Specifically in terms of the respiratory system, lower elementary-school students may not know what happens to air after it is inhaled but upper elementary-school students associate the lungs’ activities with breathing and may understand something about the exchange of gases in the lungs and that the air goes to all parts of the body. (Benchmarks for Science Literacy, p. 345.)

Planning Ahead

This lesson may need to be taught over two or three class periods. There is a brief experiment performed in the Development where students should light a candle. You could choose to do this as a demonstration instead, in which case you would just need one candle, a match, and a glass or jar.


Ask one student to come to the front of the class to blow up a balloon. He/she should hold it and then allow it to deflate. Then ask: “What organ in your body is similar to a balloon?” (The lungs.)

Refer students to the Oxygen Machine student esheet, which will guide them to The Mystery of Mallory & Irvine ’24 on the PBS website. After students have read the story, discuss the questions posed on the esheet (students can record their answers on The Oxygen Machine student sheet). Use these questions to get students started in thinking about oxygen and the body. Do not worry so much at this point about right or wrong answers.

  • What seems to be the biggest obstacle climbers faced in climbing Mount Everest?
    (The lack of enough oxygen seems to be the biggest obstacle.)
  • What is the “English Air” referred to in the story? Why did the climbers use it?
    (The English Air is oxygen stored in bottles. Climbers use it to assist breathing.)
  • Why does the human body need oxygen?
    (The human body needs oxygen so it can combust food to release the energy stored in it.)

Next, project the introductory page from Exposure on the PBS website and read the three questions on this site slowly to the students to stimulate their thinking about respiration. If you are not able to project the page to the whole class, copy the questions on the board. They are:

  • What happens to your body when it’s exposed to extreme altitudes?
  • How does the lack of oxygen affect the brain?
  • If there were a mountain higher than Everest, would humans be capable of reaching the summit?

Tell students to keep these questions in mind as they go through this lesson.

Now ask students to answer these three questions on respiration.

  • What gas in the air is important for human survival?
    (It is oxygen.)
  • What gas (which is a waste product) is exhaled from the body when breathing?
    (Carbon dioxide is exhaled from the body.)
  • What organ works in concert with the lungs?
    (The heart works in concert with the lungs.)


To help students understand the concept of respiration, review the following information with the students, which can be found on the student esheet.

“Respiration (breathing) is so automatic that we rarely think about it, unless we feel that enough air is not getting into our bodies. The drawing on the Mechanics of Respiration student sheet illustrates the basic parts of the body involved with respiration. Respiration is the process that allows us to breathe in oxygen and exhale carbon dioxide. Oxygen is then used in our cells as the fuel that transforms the food we eat into energy.”

Students will go through a series of resources to learn about: the respiration process (basic mechanics), its importance as fuel to our cells, and its importance in health and disease.

Basic Mechanics of Respiration
Using the esheet, students should go to and read the Mechanics of Respiration to learn about the process of respiration. This resource will introduce them to the structures and functions of the respiratory system.

When students have finished, review the information on the page by discussing these questions:

  • Which gases are exchanged in the process of respiration?
    (Oxygen and carbon dioxide are exchanged.)
  • Why might it be better to breathe in through the nose than through the mouth?
    (The nasal cavity has structures that clean and filter the air before it reaches your lungs.)
  • What are the four parts of your respiratory system and what do they do?
    (The nose and mouth make up the first part where air enters your body. The trachea, or windpipe, is the second part and it delivers air to the lungs. Your lungs are the third part where oxygen is absorbed by the blood, which brings it to the rest of the body. Finally, the diaphragm is the fourth part. It makes up the floor of your rib cage.)
  • What happens to air once it reaches your lungs?
    (It flows into large tubes called bronchi and from there into smaller, branching tubes called bronchioles. The bronchioles move the air into tiny air sacs called alveoli, where the oxygen is separated from the rest of the air and moved to tiny blood vessels called capillaries.)
  • What part of the blood carries oxygen to the rest of your body?
    (Hemoglobin carries oxygen to the rest of your body.)

Respiration as Combustion for the Production of Energy
Using the esheet to guide them, students should read How the Body Uses O2 on the PBS website. They should focus on #7 and #8 because they review how oxygen is involved in energy production; the other information reviews the respiration process. This site discusses atmospheric pressure, which is usually not covered in depth until high-school chemistry so you may need to define this for students if they are not familiar with it.

Students should answer these questions:

  • Why do we breathe?
    (We breathe because oxygen is needed to burn the fuel in our cells to produce energy.)
  • What happens in the process of respiration?
    (Oxygen is brought into the lungs via breathing, where it is transported by red blood cells to the entire body to be used to produce energy. Once the red blood cells return to the lungs, the “burnt” carbon dioxide is exhaled).
  • What cellular component allows the combustion process to occur?
    (The energy station of the cells, called mitochondria, process oxygen to power the cells. As part of the combustion process, carbon dioxide is released.)

Next, discuss the combustion process in terms of producing energy via respiration. You can use the information on The Oxygen Machine teacher sheet to help you with this discussion. Follow up the discussion with a simple experiment/demonstration:

Light a candle and ask students to observe the behavior of the fire for five minutes. Then put a glass or a jar on top so that the fire will eventually go out. Ask students what will happen when the glass is put on top of the fire. Also ask students what happens to the glass or anything else that comes near the flame (it gets hot because of the release of heat energy).

Now ask students to think of food again as the source of energy. Help them to establish a relationship. Begin by pointing out that fire is only one form of oxidation! Oxidation also occurs in your body: When the carbohydrates and fats in your body combine with the oxygen you inhale, they produce carbon dioxide (CO2) and release energy, oxidization.

To summarize this part of the lesson, allow students to work in small groups to answer this question: “What is the relationship between breathing and eating?” Students should explain using their own words, an example, or simply by drawing a diagram or a picture to explain the concept. (Students should discuss the relationship in terms of oxidation.)

The Importance of Respiration: Health, Fitness and Disease.
Using the esheet to guide them, students should read Hear the Experts on the PBS website and OA Guide to High Altitude: Acclimatization and Illnesses on the Princeton University website.

After students have read the information on the websites, review the information with them. You can use the text in the second part of teacher sheet to help.

To summarize and review this part of the lesson, students should answer these questions:

  • What factors affect how much oxygen your body needs?
    (Age, sex, weight, physical fitness, and level of physical activity being performed affect how much oxygen your body needs.)
  • What happens when your body doesn’t get enough oxygen?
    (Fatigue, poor concentration, fainting, hyperventilation, confusion, and possibly death are all possible effects.)
  • Can you think of a situation (either a physical activity or a medical problem) where you wouldn’t get enough oxygen?
    (Some examples include climbing, scuba diving, and an asthma attack.)
  • Would your body react differently if you ascended to the summit of Mt. Everest (29,000 feet above sea level) via a balloon ride versus taking several weeks to ascend the mountain? Why or why not?
    (Yes. If you climb, you are giving your body several weeks to adjust to the continual decrease in oxygen pressure as you get further away from sea level. In the balloon example, the body doesn’t have adequate time to make the necessary changes to adapt to the decreased oxygen pressure levels, which could lead to death.)


Give students approximately 10 minutes to write a two-paragraph summary of what they learned from this lesson. Ask for some volunteers to read what they learned.

For your use, here is a summary example:

“We depend on air for our survival. More specifically, we depend on oxygen to breathe. Without it, we would die. However, with it, we thrive. Enough oxygen must reach the tiny cells throughout our body to feed them, giving them the energy necessary for life.

A fit body can absorb more oxygen. A body that is not overweight also needs less oxygen. Fitness combined with a healthy and balanced diet is the true secret of having a healthy life!”


You can use the Making Bottled Lungs activity to extend this lesson.

Why Do We Breathe on the Canadian Lung Association website offers a basic review of respiration.

Research has shown that hyperoxia (too much oxygen) and hypoxia (too little oxygen) can damage our cells, leading to overproduction of reactive oxygen species (ROS) or free radicals (chemical derivatives of oxygen that have a free electron and because of this are very unstable and highly reactive). These websites review information about free radicals, antioxidants, and exercise:

  • Antioxidants and Free Radicals
  • Understanding Free Radicals and Antioxidants

In terms of “too much oxygen,” a great activity for students would be to research why scuba divers don’t use tanks of pure oxygen.

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The earth is surrounded by air, a mixture of extremely important gases such as oxygen, carbon dioxide, and nitrogen. These gases provide animals with oxygen for respiration to occur. It also provides green plants with carbon dioxide for photosynthesis to happen.

It is vital that living things respire to get oxygen for living cells to function. Without air, there is no life.
Plants use Carbon Dioxide (together with sunlight and water) to produce energy and give out Oxygen as a by-product. This oxygen is what almost all animals need to survive. They absorb Carbon Dioxide from the air and discharge Oxygen through very tiny pores in the leaves.
Air is also important for living organisms in the soil to survive and function. Without soil aeration, decomposers cannot work on organic matter to decompose them, as soil moisture alone is not enough for decomposition. Moving air (wind) is also important for some plants to pollinate.
Animals including humans need oxygen to live. We breathe in oxygen and breathe out Carbon Dioxide. There are also air pockets in soils and water that help tiny living things survive in water and beneath the soils. For example, fishes absorb Oxygen from the water with their gills. All animals are adapted with special organs and parts that help them absorb the oxygen they need from the air.

It’s hard to keep oxygen molecules around, despite the fact that it’s the third-most abundant element in the universe, forged in the superhot, superdense core of stars. That’s because oxygen wants to react; it can form compounds with nearly every other element on the periodic table. So how did Earth end up with an atmosphere made up of roughly 21 percent of the stuff?
The answer is tiny organisms known as cyanobacteria, or blue-green algae. These microbes conduct photosynthesis: using sunshine, water and carbon dioxide to produce carbohydrates and, yes, oxygen. In fact, all the plants on Earth incorporate symbiotic cyanobacteria (known as chloroplasts) to do their photosynthesis for them down to this day.
For some untold eons prior to the evolution of these cyanobacteria, during the Archean eon, more primitive microbes lived the real old-fashioned way: anaerobically. These ancient organisms—and their “extremophile” descendants today—thrived in the absence of oxygen, relying on sulfate for their energy needs.
But roughly 2.45 billion years ago, the isotopic ratio of sulfur transformed, indicating that for the first time oxygen was becoming a significant component of Earth’s atmosphere, according to a 2000 paper in Science. At roughly the same time (and for eons thereafter), oxidized iron began to appear in ancient soils and bands of iron were deposited on the seafloor, a product of reactions with oxygen in the seawater.
“What it looks like is that oxygen was first produced somewhere around 2.7 billion to 2.8 billon years ago. It took up residence in atmosphere around 2.45 billion years ago,” says geochemist Dick Holland, a visiting scholar at the University of Pennsylvania. “It looks as if there’s a significant time interval between the appearance of oxygen-producing organisms and the actual oxygenation of the atmosphere.”
So a date and a culprit can be fixed for what scientists refer to as the Great Oxidation Event, but mysteries remain. What occurred 2.45 billion years ago that enabled cyanobacteria to take over? What were oxygen levels at that time? Why did it take another one billion years—dubbed the “boring billion” by scientists—for oxygen levels to rise high enough to enable the evolution of animals?
Most important, how did the amount of atmospheric oxygen reach its present level? “It’s not that easy why it should balance at 21 percent rather than 10 or 40 percent,” notes geoscientist James Kasting of Pennsylvania State University. “We don’t understand the modern oxygen control system that well.”
Climate, volcanism, plate tectonics all played a key role in regulating the oxygen level during various time periods. Yet no one has come up with a rock-solid test to determine the precise oxygen content of the atmosphere at any given time from the geologic record. But one thing is clear—the origins of oxygen in Earth’s atmosphere derive from one thing: life.

How the Earth Works

The Earth’s atmosphere is mostly composed of nitrogen. Oxygen makes up just 21 percent of the air we breathe. Carbon dioxide, argon, ozone, water vapor and other gasses make up a tiny portion of it, as little as 1 percent. These gasses probably came from several processes as the Earth evolved and grew as a planet.

But some scientists believe that the Earth’s atmosphere would never have contained the oxygen we need without plants. Plants (and some bacteria) release oxygen during photosynthesis, the process they use to change water and carbon dioxide into sugar they can use for food.


Photosynthesis is a complex reaction. In a lot of ways, it’s similar to the way your body breaks down food into fuel that it can store. Essentially, using energy from the sun, a plant can transform carbon dioxide and water into glucose and oxygen. In chemical terms:

6CO2 + 12H2O + Light -> C6H12O6 + 6O2+ 6H2O

In other words, while we inhale oxygen and exhale carbon dioxide, plants inhale carbon dioxide and exhale oxygen. Some scientists believe that our atmosphere had little to no oxygen before plants evolved and started releasing it.

Without the sun to feed plants (and the plants to release oxygen), we might not have breathable air. Without plants to feed us and the animals most people use for food, we’d also have nothing to eat.

Obviously, plants are important, but not just because they give us food to eat and oxygen to breathe. Plants help control the amount of carbon dioxide, a greenhouse gas, in the atmosphere. They protect the soil from wind and from water runoff, helping to control erosion. In addition, they release water into the air during photosynthesis. This water, along with the rest of the water on the planet, takes part in a huge cycle that the sun controls. We’ll look at this cycle on the next page.

All living things use a process called respiration to get energy to stay alive. Cellular respiration in plants is the process used by plants to convert nutrients obtained from soil into energy which fuels the plants’ cellular activities.

On the other hand, photosynthesis is the process where light energy is converted into chemical energy stored in glucose that can later be used in respiration. on the green parts of the plant that contain chlorophyll.

During respiration, plants consume nutrients to keep plant cells alive while during photosynthesis, plants create their own food.

Plant Respiration And Photosynthesis Formula

oxygen + glucose -> carbon dioxide + water + heat energy

carbon dioxide + water+ light energy -> oxygen + glucose

Plants respire all the time, day and night. But photosynthesis only occurs during the day when there is sunlight.

Depending on the amount of sunlight, plants can give out or take in oxygen and carbon dioxide as follows​1​.

Dark – Only respiration takes place. Oxygen is consumed while carbon dioxide is released.

Dim sunlight – Photosynthesis rate equals respiration rate. A plant consumes all the oxygen photosynthesis generates. It also uses all the carbon dioxide respiration creates. As a result, no gas exchange takes place with the environment.

Bright sunlight – Photosynthesis uses carbon dioxide and makes oxygen faster than respiration produces carbon dioxide and consumes oxygen. Extra oxygen is released into the atmosphere.

During daytime, photosynthesis produces oxygen and glucose faster than respiration consumes it. Photosynthesis also uses carbon dioxide faster than respiration produces it. Oxygen surplus is released into the air and unused glucose stored in the plant for later use.

This is why plants are so important to human and other animals’ survival. Without photosynthesis, we wouldn’t have oxygen or food to stay alive.

What Is The Difference Between Cellular Respiration And Breathing

People breathe. Animals breathe. Do plants breathe?

Breathing refers to the act of inhaling air into the lung and then expelling it out of the bodies afterwards. So it’s a physical process of exchanging gases between the living objects and the environment.

Plants do not breathe in the strictest sense of the word. Plants respire.

During respiration and photosynthesis, gases go in and out of the plants through little holes called stomata using diffusion, not breathing.

But in everyday lives, we use those words slightly differently because we are not all biologists or chemists.

Respiration in plants is strikingly similar to why living objects breathe.

Living objects breathe because they need to obtain oxygen to carry out cellular respiration to stay alive, just like plants need to respire to stay alive. Then byproducts such as carbon dioxide and water are released and removed from the living objects through breathing, just like plants do when they respire.

Because of these parallel processes, people sometimes imprecisely call respiration in plants as “breathing”.

This is why it is not entirely incorrect if you’re not using this as an answer in exams, but rather, just use it as an analogy. Plants don’t breathe in and out using lungs, but it is an analogy nonetheless.

Prep Time: 5 minutes Active Time: 10 minutes Additional Time: 1 hour Total Time: 1 hour 15 minutes

Here is a popular science experiment to visually see how plants “breathe”.

In this experiment, we can see how gases produced during photosynthesis and respiration are released into the environment.


  • water
  • plant (e.g. a flower or a leaf. Pick it from a living plant, not one that has fallen onto the ground)
  • sunlight (optional)


  • shallow bowl



  1. Submerge the plant into a bowl of water. The flower or leaf may float to the top, but try to make at least part of the plant stay underwater.
  2. Put the bowl under the sunlight and wait. (You can also leave it in the dark but it may take longer to see results.)
  3. After an hour, observe the plant’s surface. There should be some air bubbles formed on the pedals or the leaf.


  1. Observe different parts of the plant. Do air bubbles form everywhere?
  2. Do air bubbles form if you leave the plant in the dark?

Oxygen and carbon dioxide pass in and out of the stomata in the plants through diffusion.

When the plant is submerged in the water, bubbles of oxygen or carbon dioxide released are trapped and they stick on the leaves or petals temporarily.

Since these gases are lighter than water, if you shake the plant, the bubbles will quickly rise to the surface and burst. It is similar to you releasing a breath underwater.

Books On Plants, Photosynthesis And Respiration

This is Book 8 in the Super Smart Science book series.

This colorful picture book is a great introduction to botany. It teaches key vocabulary such as leaf, stem, root, xylem, cellulose, chloroplast, photosynthesis and respiration, and the pronunciation. It is thorough and easy to understand.

Other topics covered in the series including biology, chemistry, astronomy, anatomy and physiology are also great additions to kids’ library.

This book presents a lot of fun facts about plants. For example, did you know that planting one tree produces enough oxygen to support four people for one year?

Scientific concepts such as photosynthesis is well explained by excellent graphics and interesting stories about Max Axiom. Max is a super hero and a super scientist. He really helps make science learning fun.

This book presents a lot of fun facts about plants. For example, did you know that planting one tree produces enough oxygen to support four people for one year?

Scientific concepts such as photosynthesis is well explained by excellent graphics and interesting stories about Max Axiom. Max is a super hero and a super scientist. He really helps make science learning fun.

  • Photosynthesis
  • How Plants Work: The Science Behind the Amazing Things Plants Do
  1. 1. Makino A, Mae T. Photosynthesis and Plant Growth at Elevated Levels of CO2. Plant and Cell Physiology. January 1999:999-1006. doi:10.1093/oxfordjournals.pcp.a029493

Earth’s atmosphere wasn’t always full of life-giving oxygen — it was once a choking mixture of carbon dioxide and other gases, more like the atmosphere of Mars or Venus.

It’s widely believed that the rise of plants turned that carbon dioxide into oxygen through the chemical reactions of photosynthesis, in a period called the Great Oxygenation Event. But a new study suggests there may be another way to make oxygen from carbon dioxide, using ultraviolet light.

The findings could explain how the Earth’s atmosphere evolved, and hint at a way to make oxygen in space, the researchers said.

Even though scientists think plants produced most of the oxygen present on Earth, they suspected some oxygen may have existed before photosynthetic organisms arose, said Cheuk-Yiu Ng, a physical chemist at the University of California, Davis, and co-author of the study published today (Oct. 2) in the journal Science.

But, it was thought that the planet’s oxygen (O2) formed from two oxygen atoms colliding and combining on some surface, not because the oxygen molecules split from carbon dioxide (CO2), Ng said.

When light breaks apart CO2, the molecule normally splits into carbon monoxide (CO) and an oxygen atom (O). One theory suggested carbon dioxide could potentially be stripped into molecular oxygen (O2) and carbon (C) instead, but “nobody had ever detected” such a process, Ng told Live Science.

Ng and his colleagues built a one-of-a-kind instrument to split up carbon dioxide, using ultraviolet light in a vacuum. The device consists of two lasers — one to split the CO2, and one to detect the fragments produced.

“This machine is unique in the world,” Ng said.

When the researchers shone the first laser on the carbon dioxide, the second laser detected O2 molecules and carbon atoms, suggesting a small amount of carbon dioxide (about 5 percent) was turned into oxygen. Though small, that’s enough to show that it’s possible to produce oxygen from CO2 by a nonbiological process, Ng said.

The findings reveal a possible way oxygen entered the atmosphere of Earth and other planets, the researchers said. This has implications on the search for extraterrestrial life, suggesting that merely detecting oxygen in the atmosphere of another planet is not enough to signify the presence of life, Ng said.

Finally, the researchers hinted that it may be possible to use this technique to make oxygen in space or on other planets. But first, more studies are needed to verify the fundamentals of how this reaction occurs, the scientists said.

One reason the experiment hadn’t been done before is because of the difficulty of creating intense vacuum ultraviolet light, Ng said. One way is to use a particle accelerator called a synchrotron, but the laser in Ng’s lab is 10,000 to 1 million times brighter than those produced by existing synchrotrons, he said.

Follow Tanya Lewis on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

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