where is the end product of photosynthesis stored in plants

• COVID-19 Tracker
• Biochemistry
• Anatomy & Physiology
• Microbiology
• Neuroscience
• Animal Kingdom
• NGSS High School
• Latest News
• Editors’ Picks
• Weekly Digest
• Quotes about Biology

Photosynthesis

Reviewed by: BD Editors

Photosynthesis Definition

Photosynthesis is the biochemical pathway which converts the energy of light into the bonds of glucose molecules. The process of photosynthesis occurs in two steps. In the first step, energy from light is stored in the bonds of adenosine triphosphate (ATP), and nicotinamide adenine dinucleotide phosphate (NADPH). These two energy-storing cofactors are then used in the second step of photosynthesis to produce organic molecules by combining carbon molecules derived from carbon dioxide (CO 2 ). The second step of photosynthesis is known as the Calvin Cycle. These organic molecules can then be used by mitochondria to produce ATP, or they can be combined to form glucose, sucrose, and other carbohydrates. The chemical equation for the entire process can be seen below.

Photosynthesis Equation

Above is the overall reaction for photosynthesis. Using the energy from light and the hydrogens and electrons from water, the plant combines the carbons found in carbon dioxide into more complex molecules. While a 3-carbon molecule is the direct result of photosynthesis, glucose is simply two of these molecules combined and is often represented as the direct result of photosynthesis due to glucose being a foundational molecule in many cellular systems. You will also notice that 6 gaseous oxygen molecules are produced, as a by-produce. The plant can use this oxygen in its mitochondria during oxidative phosphorylation . While some of the oxygen is used for this purpose, a large portion is expelled into the atmosphere and allows us to breathe and undergo our own oxidative phosphorylation, on sugar molecules derived from plants. You will also notice that this equation shows water on both sides. That is because 12 water molecules are split during the light reactions, while 6 new molecules are produced during and after the Calvin cycle. While this is the general equation for the entire process, there are many individual reactions which contribute to this pathway.

Stages of Photosynthesis

The light reactions.

The light reactions happen in the thylakoid membranes of the chloroplasts of plant cells. The thylakoids have densely packed protein and enzyme clusters known as photosystems . There are two of these systems, which work in conjunction with each other to remove electrons and hydrogens from water and transfer them to the cofactors ADP and NADP + . These photosystems were named in the order of which they were discovered, which is opposite of how electrons flow through them. As seen in the image below, electrons excited by light energy flow first through photosystem II (PSII), and then through photosystem I (PSI) as they create NADPH. ATP is created by the protein ATP synthase , which uses the build-up of hydrogen atoms to drive the addition of phosphate groups to ADP.

The entire system works as follows. A photosystem is comprised of various proteins that surround and connect a series of pigment molecules . Pigments are molecules that absorb various photons, allowing their electrons to become excited. Chlorophyll a is the main pigment used in these systems, and collects the final energy transfer before releasing an electron. Photosystem II starts this process of electrons by using the light energy to split a water molecule, which releases the hydrogen while siphoning off the electrons. The electrons are then passed through plastoquinone, an enzyme complex that releases more hydrogens into the thylakoid space . The electrons then flow through a cytochrome complex and plastocyanin to reach photosystem I. These three complexes form an electron transport chain , much like the one seen in mitochondria. Photosystem I then uses these electrons to drive the reduction of NADP + to NADPH. The additional ATP made during the light reactions comes from ATP synthase, which uses the large gradient of hydrogen molecules to drive the formation of ATP.

The Calvin Cycle

With its electron carriers NADPH and ATP all loaded up with electrons, the plant is now ready to create storable energy. This happens during the Calvin Cycle , which is very similar to the citric acid cycle seen in mitochondria. However, the citric acid cycle creates ATP other electron carriers from 3-carbon molecules, while the Calvin cycle produces these products with the use of NADPH and ATP. The cycle has 3 phases, as seen in the graphic below.

During the first phase, a carbon is added to a 5-carbon sugar, creating an unstable 6-carbon sugar. In phase two, this sugar is reduced into two stable 3-carbon sugar molecules. Some of these molecules can be used in other metabolic pathways, and are exported. The rest remain to continue cycling through the Calvin cycle. During the third phase, the five-carbon sugar is regenerated to start the process over again. The Calvin cycle occurs in the stroma of a chloroplast. While not considered part of the Calvin cycle, these products can be used to create a variety of sugars and structural molecules.

Products of Photosynthesis

The direct products of the light reactions and the Calvin cycle are 3-phosphoglycerate and G3P, two different forms of a 3-carbon sugar molecule. Two of these molecules combined equals one glucose molecule, the product seen in the photosynthesis equation. While this is the main food source for plants and animals, these 3-carbon skeletons can be combined into many different forms. A structural form worth note is cellulose , and extremely strong fibrous material made essentially of strings of glucose. Besides sugars and sugar-based molecules, oxygen is the other main product of photosynthesis. Oxygen created from photosynthesis fuels every respiring organism on the planet.

Lodish, H., Berk, A., Kaiser, C. A., Krieger, M., Scott, M. P., Bretscher, A., . . . Matsudaira, P. (2008). Molecular Cell Biology 6th. ed . New York: W.H. Freeman and Company. Nelson, D. L., & Cox, M. M. (2008). Principles of Biochemistry . New York: W.H. Freeman and Company.

Cite This Article

Subscribe to our newsletter, privacy policy, terms of service, scholarship, latest posts, white blood cell, t cell immunity, satellite cells, embryonic stem cells, popular topics, hermaphrodite, adenosine triphosphate (atp), acetic acid, cellular respiration, translation.

• History & Society
• Science & Tech
• Biographies
• Animals & Nature
• Geography & Travel
• Arts & Culture
• Games & Quizzes
• On This Day
• One Good Fact
• New Articles
• Lifestyles & Social Issues
• Philosophy & Religion
• Politics, Law & Government
• World History
• Health & Medicine
• Browse Biographies
• Birds, Reptiles & Other Vertebrates
• Bugs, Mollusks & Other Invertebrates
• Environment
• Fossils & Geologic Time
• Entertainment & Pop Culture
• Sports & Recreation
• Visual Arts
• Demystified
• Image Galleries
• Infographics
• Top Questions
• Britannica Kids
• Saving Earth
• Space Next 50
• Student Center
• Introduction & Top Questions
• Development of the idea
• Overall reaction of photosynthesis

Basic products of photosynthesis

Evolution of the process, light intensity and temperature.

• Carbon dioxide
• Internal factors
• Energy efficiency of photosynthesis
• Structural features
• Light absorption and energy transfer
• The pathway of electrons
• Evidence of two light reactions
• Photosystems I and II
• Quantum requirements
• The process of photosynthesis: the conversion of light energy to ATP
• Elucidation of the carbon pathway
• Carboxylation
• Isomerization/condensation/dismutation
• Phosphorylation
• Regulation of the cycle
• Products of carbon reduction
• Photorespiration
• Carbon fixation in C 4 plants
• Carbon fixation via crassulacean acid metabolism (CAM)
• Differences in carbon fixation pathways
• The molecular biology of photosynthesis

• Why is photosynthesis important?
• What is the basic formula for photosynthesis?
• Which organisms can photosynthesize?

Our editors will review what you’ve submitted and determine whether to revise the article.

• Khan Academy - Photosynthesis
• Biology LibreTexts - Photosynthesis
• University of Florida - Institute of Food and Agricultural Sciences - Photosynthesis
• Milne Library - Inanimate Life - Photosynthesis
• National Center for Biotechnology Information - Chloroplasts and Photosynthesis
• Roger Williams University Pressbooks - Introduction to Molecular and Cell Biology - Photosynthesis
• BCcampus Open Publishing - Concepts of Biology – 1st Canadian Edition - Overview of Photosynthesis
• photosynthesis - Children's Encyclopedia (Ages 8-11)
• photosynthesis - Student Encyclopedia (Ages 11 and up)
• Table Of Contents

Recent News

Little free glucose is produced in plants; instead, glucose units are linked to form starch or are joined with fructose , another sugar , to form sucrose ( see carbohydrate ).

Not only carbohydrates, as was once thought, but also amino acids, proteins, lipids (or fats), pigments , and other organic components of green tissues are synthesized during photosynthesis. Minerals supply the elements (e.g., nitrogen , N; phosphorus , P; sulfur , S) required to form these compounds . Chemical bonds are broken between oxygen (O) and carbon (C), hydrogen (H), nitrogen , and sulfur, and new bonds are formed in products that include gaseous oxygen (O 2 ) and organic compounds. More energy is required to break the bonds between oxygen and other elements (e.g., in water , nitrate, and sulfate) than is released when new bonds form in the products. This difference in bond energy accounts for a large part of the light energy stored as chemical energy in the organic products formed during photosynthesis. Additional energy is stored in making complex molecules from simple ones.

Although life and the quality of the atmosphere today depend on photosynthesis, it is likely that green plants evolved long after the first living cells . When Earth was young, electrical storms and solar radiation probably provided the energy for the synthesis of complex molecules from abundant simpler ones, such as water, ammonia , and methane . The first living cells probably evolved from these complex molecules ( see life: Production of polymers ). For example, the accidental joining (condensation) of the amino acid glycine and the fatty acid acetate may have formed complex organic molecules known as porphyrins . These molecules, in turn, may have evolved further into colored molecules called pigments —e.g., chlorophylls of green plants, bacteriochlorophyll of photosynthetic bacteria, hemin (the red pigment of blood), and cytochromes , a group of pigment molecules essential in both photosynthesis and cellular respiration .

Primitive colored cells then had to evolve mechanisms for using the light energy absorbed by their pigments. At first, the energy may have been used immediately to initiate reactions useful to the cell . As the process for utilization of light energy continued to evolve, however, a larger part of the absorbed light energy probably was stored as chemical energy, to be used to maintain life. Green plants, with their ability to use light energy to convert carbon dioxide and water to carbohydrates and oxygen, are the culmination of this evolutionary process.

The first oxygenic (oxygen-producing) cells probably were the blue-green algae (cyanobacteria), which appeared about two billion to three billion years ago. These microscopic organisms are believed to have greatly increased the oxygen content of the atmosphere, making possible the development of aerobic (oxygen-using) organisms. Cyanophytes are prokaryotic cells ; that is, they contain no distinct membrane -enclosed subcellular particles ( organelles ), such as nuclei and chloroplasts . Green plants, by contrast, are composed of eukaryotic cells , in which the photosynthetic apparatus is contained within membrane-bound chloroplasts. The complete genome sequences of cyanobacteria and higher plants provide evidence that the first photosynthetic eukaryotes were likely the red algae that developed when nonphotosynthetic eukaryotic cells engulfed cyanobacteria. Within the host cells, these cyanobacteria evolved into chloroplasts.

There are a number of photosynthetic bacteria that are not oxygenic (e.g., the sulfur bacteria previously discussed). The evolutionary pathway that led to these bacteria diverged from the one that resulted in oxygenic organisms. In addition to the absence of oxygen production, nonoxygenic photosynthesis differs from oxygenic photosynthesis in two other ways: light of longer wavelengths is absorbed and used by pigments called bacteriochlorophylls, and reduced compounds other than water (such as hydrogen sulfide or organic molecules) provide the electrons needed for the reduction of carbon dioxide.

Factors that influence the rate of photosynthesis

The rate of photosynthesis is defined in terms of the rate of oxygen production either per unit mass (or area) of green plant tissues or per unit weight of total chlorophyll . The amount of light, the carbon dioxide supply, temperature , water supply , and the availability of minerals are the most important environmental factors that affect the rate of photosynthesis in land plants. The rate of photosynthesis is also determined by the plant species and its physiological state—e.g., its health , its maturity, and whether it is in flower .

As has been mentioned, the complex mechanism of photosynthesis includes a photochemical, or light-harvesting, stage and an enzymatic, or carbon-assimilating, stage that involves chemical reactions. These stages can be distinguished by studying the rates of photosynthesis at various degrees of light saturation (i.e., intensity) and at different temperatures . Over a range of moderate temperatures and at low to medium light intensities (relative to the normal range of the plant species), the rate of photosynthesis increases as the intensity increases and is relatively independent of temperature. As the light intensity increases to higher levels, however, the rate becomes saturated; light “saturation” is achieved at a specific light intensity, dependent on species and growing conditions. In the light-dependent range before saturation, therefore, the rate of photosynthesis is determined by the rates of photochemical steps. At high light intensities, some of the chemical reactions of the dark stage become rate-limiting. In many land plants, a process called photorespiration occurs, and its influence upon photosynthesis increases with rising temperatures. More specifically, photorespiration competes with photosynthesis and limits further increases in the rate of photosynthesis, especially if the supply of water is limited ( see below Photorespiration ).

8. Photosynthesis

Overview of photosynthesis, learning objectives.

By the end of this section, you will be able to do the following:

• Explain the significance of photosynthesis to other living organisms
• Describe the main structures involved in photosynthesis
• Identify the substrates and products of photosynthesis

Photosynthesis is essential to all life on earth; both plants and animals depend on it. It is the only biological process that can capture energy that originates from sunlight and converts it into chemical compounds (carbohydrates) that every organism uses to power its metabolism. It is also a source of oxygen necessary for many living organisms. In brief, the energy of sunlight is “captured” to energize electrons, whose energy is then stored in the covalent bonds of sugar molecules. How long lasting and stable are those covalent bonds? The energy extracted today by the burning of coal and petroleum products represents sunlight energy captured and stored by photosynthesis 350 to 200 million years ago during the Carboniferous Period.

Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis ( (Figure) ). Because they use light to manufacture their own food, they are called photoautotrophs (literally, “self-feeders using light”). Other organisms, such as animals, fungi, and most other bacteria, are termed heterotrophs (“other feeders”), because they must rely on the sugars produced by photosynthetic organisms for their energy needs. A third very interesting group of bacteria synthesize sugars, not by using sunlight’s energy, but by extracting energy from inorganic chemical compounds. For this reason, they are referred to as chemoautotrophs.

Figure 1. Photoautotrophs including (a) plants, (b) algae, and (c) cyanobacteria synthesize their organic compounds via photosynthesis using sunlight as an energy source. Cyanobacteria and planktonic algae can grow over enormous areas in water, at times completely covering the surface. In a (d) deep sea vent, chemoautotrophs, such as these (e) thermophilic bacteria, capture energy from inorganic compounds to produce organic compounds. The ecosystem surrounding the vents has a diverse array of animals, such as tubeworms, crustaceans, and octopuses that derive energy from the bacteria. (credit a: modification of work by Steve Hillebrand, U.S. Fish and Wildlife Service; credit b: modification of work by “eutrophication&hypoxia”/Flickr; credit c: modification of work by NASA; credit d: University of Washington, NOAA; credit e: modification of work by Mark Amend, West Coast and Polar Regions Undersea Research Center, UAF, NOAA)

The importance of photosynthesis is not just that it can capture sunlight’s energy. After all, a lizard sunning itself on a cold day can use the sun’s energy to warm up in a process called behavioral thermoregulation . In contrast, photosynthesis is vital because it evolved as a way to store the energy from solar radiation (the “photo-” part) to energy in the carbon-carbon bonds of carbohydrate molecules (the “-synthesis” part). Those carbohydrates are the energy source that heterotrophs use to power the synthesis of ATP via respiration. Therefore, photosynthesis powers 99 percent of Earth’s ecosystems. When a top predator, such as a wolf, preys on a deer ( (Figure) ), the wolf is at the end of an energy path that went from nuclear reactions on the surface of the sun, to visible light, to photosynthesis, to vegetation, to deer, and finally to the wolf.

Figure 2. The energy stored in carbohydrate molecules from photosynthesis passes through the food chain. The predator that eats these deer receives a portion of the energy that originated in the photosynthetic vegetation that the deer consumed. (credit: modification of work by Steve VanRiper, U.S. Fish and Wildlife Service)

Main Structures and Summary of Photosynthesis

Photosynthesis is a multi-step process that requires specific wavelengths of visible sunlight, carbon dioxide (which is low in energy), and water as substrates ( (Figure) ). After the process is complete, it releases oxygen and produces glyceraldehyde-3-phosphate (GA3P), as well as simple carbohydrate molecules (high in energy) that can then be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy and the energized carbon that all living things need to survive.

Figure 3. Photosynthesis uses solar energy, carbon dioxide, and water to produce energy-storing carbohydrates. Oxygen is generated as a waste product of photosynthesis.

The following is the chemical equation for photosynthesis ( (Figure) ):

Figure 4. The basic equation for photosynthesis is deceptively simple. In reality, the process takes place in many steps involving intermediate reactants and products. Glucose, the primary energy source in cells, is made from two three-carbon GA3Ps.

Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the structures involved.

Basic Photosynthetic Structures

In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells. The process of photosynthesis occurs in a middle layer called the mesophyll. The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata (singular: stoma), which also play roles in the regulation of gas exchange and water balance. The stomata are typically located on the underside of the leaf, which helps to minimize water loss due to high temperatures on the upper surface of the leaf. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes.

In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast. For plants, chloroplast-containing cells exist mostly in the mesophyll. Chloroplasts have a double membrane envelope (composed of an outer membrane and an inner membrane), and are ancestrally derived from ancient free-living cyanobacteria. Within the chloroplast are stacked, disc-shaped structures called thylakoids. Embedded in the thylakoid membrane is chlorophyll, a pigment (molecule that absorbs light) responsible for the initial interaction between light and plant material, and numerous proteins that make up the electron transport chain. The thylakoid membrane encloses an internal space called the thylakoid lumen. As shown in (Figure) , a stack of thylakoids is called a granum, and the liquid-filled space surrounding the granum is called stroma or “bed” (not to be confused with stoma or “mouth,” an opening on the leaf epidermis).

Art Connection

Figure 5. Photosynthesis takes place in chloroplasts, which have an outer membrane and an inner membrane. Stacks of thylakoids called grana form a third membrane layer.

On a hot, dry day, the guard cells of plants close their stomata to conserve water. What impact will this have on photosynthesis?

Levels of carbon dioxide (a necessary photosynthetic substrate) will fall. As a result, the rate of photosynthesis will decrease.

The Two Parts of Photosynthesis

Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light-independent reactions. In the light-dependent reactions, energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy. In the light-independent reactions, the chemical energy harvested during the light-dependent reactions drives the assembly of sugar molecules from carbon dioxide. Therefore, although the light-independent reactions do not use light as a reactant, they require the products of the light-dependent reactions to function. In addition, however, several enzymes of the light-independent reactions are activated by light. The light-dependent reactions utilize certain molecules to temporarily store the energy: These are referred to as energy carriers . The energy carriers that move energy from light-dependent reactions to light-independent reactions can be thought of as “full” because they are rich in energy. After the energy is released, the “empty” energy carriers return to the light-dependent reaction to obtain more energy. (Figure) illustrates the components inside the chloroplast where the light-dependent and light-independent reactions take place.

Figure 6. Photosynthesis takes place in two stages: light-dependent reactions and the Calvin cycle. Light-dependent reactions, which take place in the thylakoid membrane, use light energy to make ATP and NADPH. The Calvin cycle, which takes place in the stroma, uses energy derived from these compounds to make GA3P from CO2.

Link to Learning

Click the link to learn more about photosynthesis.

Everyday Connection

Photosynthesis at the Grocery Store

Figure 7. Foods that humans consume originate from photosynthesis. (credit: Associação Brasileira de Supermercados)

Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle ( (Figure) ) contains hundreds, if not thousands, of different products for customers to buy and consume.

Although there is a large variety, each item ultimately can be linked back to photosynthesis. Meats and dairy link, because the animals were fed plant-based foods. The breads, cereals, and pastas come largely from starchy grains, which are the seeds of photosynthesis-dependent plants. What about desserts and drinks? All of these products contain sugar—sucrose is a plant product, a disaccharide, a carbohydrate molecule, which is built directly from photosynthesis. Moreover, many items are less obviously derived from plants: For instance, paper goods are generally plant products, and many plastics (abundant as products and packaging) are derived from “algae” (unicellular plant-like organisms, and cyanobacteria). Virtually every spice and flavoring in the spice aisle was produced by a plant as a leaf, root, bark, flower, fruit, or stem. Ultimately, photosynthesis connects to every meal and every food a person consumes.

Section Summary

The process of photosynthesis transformed life on Earth. By harnessing energy from the sun, the evolution of photosynthesis allowed living things access to enormous amounts of energy. Because of photosynthesis, living things gained access to sufficient energy that allowed them to build new structures and achieve the biodiversity evident today.

Only certain organisms (photoautotrophs), can perform photosynthesis; they require the presence of chlorophyll, a specialized pigment that absorbs certain wavelengths of the visible spectrum and can capture energy from sunlight. Photosynthesis uses carbon dioxide and water to assemble carbohydrate molecules and release oxygen as a byproduct into the atmosphere. Eukaryotic autotrophs, such as plants and algae, have organelles called chloroplasts in which photosynthesis takes place, and starch accumulates. In prokaryotes, such as cyanobacteria, the process is less localized and occurs within folded membranes, extensions of the plasma membrane, and in the cytoplasm.

Art Connections

(Figure) On a hot, dry day, plants close their stomata to conserve water. What impact will this have on photosynthesis?

(Figure) Levels of carbon dioxide (a necessary photosynthetic substrate) will immediately fall. As a result, the rate of photosynthesis will be inhibited.

Review Questions

Which of the following components is not used by both plants and cyanobacteria to carry out photosynthesis?

• chloroplasts
• chlorophyll
• carbon dioxide

What two main products result from photosynthesis?

• oxygen and carbon dioxide
• chlorophyll and oxygen
• sugars/carbohydrates and oxygen
• sugars/carbohydrates and carbon dioxide

In which compartment of the plant cell do the light-independent reactions of photosynthesis take place?

• outer membrane

Which statement about thylakoids in eukaryotes is not correct?

• Thylakoids are assembled into stacks.
• Thylakoids exist as a maze of folded membranes.
• The space surrounding thylakoids is called stroma.
• Thylakoids contain chlorophyll.

Predict the end result if a chloroplast’s light-independent enzymes developed a mutation that prevented them from activating in response to light.

• GA3P accumulation
• ATP and NADPH accumulation
• Water accumulation
• Carbon dioxide depletion

Show Solution

How are the NADPH and GA3P molecules made during photosynthesis similar?

• They are both end products of photosynthesis.
• They are both substrates for photosynthesis.
• They are both produced from carbon dioxide.
• They both store energy in chemical bonds.

Free Response

What is the overall outcome of the light reactions in photosynthesis?

The outcome of light reactions in photosynthesis is the conversion of solar energy into chemical energy that the chloroplasts can use to do work (mostly anabolic production of carbohydrates from carbon dioxide).

Why are carnivores, such as lions, dependent on photosynthesis to survive?

Because lions eat animals that eat plants.

Why are energy carriers thought of as either “full” or “empty”?

The energy carriers that move from the light-dependent reaction to the light-independent one are “full” because they bring energy. After the energy is released, the “empty” energy carriers return to the light-dependent reaction to obtain more energy. There is not much actual movement involved. Both ATP and NADPH are produced in the stroma where they are also used and reconverted into ADP, Pi, and NADP+.

Describe how the grey wolf population would be impacted by a volcanic eruption that spewed a dense ash cloud that blocked sunlight in a section of Yellowstone National Park.

The grey wolves are apex predators in their food web, meaning they consume smaller prey animals and are not the prey of any other animal. Blocking sunlight would prevent the plants at the bottom of the food web from performing photosynthesis. This would kill many of the plants, reducing the food sources available to smaller animals in Yellowstone. A smaller prey animal population means that fewer wolves can survive in the area, and the population of grey wolves will decrease.

How does the closing of the stomata limit photosynthesis?

The stomata regulate the exchange of gases and water vapor between a leaf and its surrounding environment. When the stomata are closed, the water molecules cannot escape the leaf, but the leaf also cannot acquire new carbon dioxide molecules from the environment. This limits the light-independent reactions to only continuing until the carbon dioxide stores in the leaf are depleted.

• Biology 2e. Provided by : OpenStax. Located at : https://openstax.org/details/books/biology-2e . License : CC BY: Attribution . License Terms : Download for free at http://cnx.org/contents/[email protected]

Privacy Policy

ENCYCLOPEDIC ENTRY

Photosynthesis.

Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.

Loading ...

Learning materials, instructional links.

• Photosynthesis (Google doc)

Most life on Earth depends on photosynthesis .The process is carried out by plants, algae, and some types of bacteria, which capture energy from sunlight to produce oxygen (O 2 ) and chemical energy stored in glucose (a sugar). Herbivores then obtain this energy by eating plants, and carnivores obtain it by eating herbivores.

The process

During photosynthesis, plants take in carbon dioxide (CO 2 ) and water (H 2 O) from the air and soil. Within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose. The plant then releases the oxygen back into the air, and stores energy within the glucose molecules.

Chlorophyll

Inside the plant cell are small organelles called chloroplasts , which store the energy of sunlight. Within the thylakoid membranes of the chloroplast is a light-absorbing pigment called chlorophyll , which is responsible for giving the plant its green color. During photosynthesis , chlorophyll absorbs energy from blue- and red-light waves, and reflects green-light waves, making the plant appear green.

Light-dependent Reactions vs. Light-independent Reactions

While there are many steps behind the process of photosynthesis, it can be broken down into two major stages: light-dependent reactions and light-independent reactions. The light-dependent reaction takes place within the thylakoid membrane and requires a steady stream of sunlight, hence the name light- dependent reaction. The chlorophyll absorbs energy from the light waves, which is converted into chemical energy in the form of the molecules ATP and NADPH . The light-independent stage, also known as the Calvin cycle , takes place in the stroma , the space between the thylakoid membranes and the chloroplast membranes, and does not require light, hence the name light- independent reaction. During this stage, energy from the ATP and NADPH molecules is used to assemble carbohydrate molecules, like glucose, from carbon dioxide.

C3 and C4 Photosynthesis

Not all forms of photosynthesis are created equal, however. There are different types of photosynthesis, including C3 photosynthesis and C4 photosynthesis. C3 photosynthesis is used by the majority of plants. It involves producing a three-carbon compound called 3-phosphoglyceric acid during the Calvin Cycle, which goes on to become glucose. C4 photosynthesis, on the other hand, produces a four-carbon intermediate compound, which splits into carbon dioxide and a three-carbon compound during the Calvin Cycle. A benefit of C4 photosynthesis is that by producing higher levels of carbon, it allows plants to thrive in environments without much light or water. The National Geographic Society is making this content available under a Creative Commons CC-BY-NC-SA license . The License excludes the National Geographic Logo (meaning the words National Geographic + the Yellow Border Logo) and any images that are included as part of each content piece. For clarity the Logo and images may not be removed, altered, or changed in any way.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Production Managers

Program specialists, last updated.

June 21, 2024

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources

• News/Events
• Arts and Sciences
• Design and the Arts
• Engineering
• Global Futures
• Health Solutions
• Nursing and Health Innovation
• Public Service and Community Solutions
• University College
• Thunderbird School of Global Management
• Polytechnic
• Downtown Phoenix
• Online and Extended
• Lake Havasu
• Research Park
• Washington D.C.
• Biology Bits
• Bird Finder
• Coloring Pages
• Experiments and Activities
• Games and Simulations
• Quizzes in Other Languages
• Virtual Reality (VR)
• World of Biology
• Meet Our Biologists
• Listen and Watch
• PLOSable Biology
• All About Autism
• Xs and Ys: How Our Sex Is Decided
• When Blood Types Shouldn’t Mix: Rh and Pregnancy
• What Is the Menstrual Cycle?
• Understanding Intersex
• The Mysterious Case of the Missing Periods
• Summarizing Sex Traits
• Shedding Light on Endometriosis
• Periods: What Should You Expect?
• Menstruation Matters
• Investigating In Vitro Fertilization
• Introducing the IUD
• How Fast Do Embryos Grow?
• Helpful Sex Hormones
• Getting to Know the Germ Layers
• Gender versus Biological Sex: What’s the Difference?
• Gender Identities and Expression
• Focusing on Female Infertility
• Fetal Alcohol Syndrome and Pregnancy
• Ectopic Pregnancy: An Unexpected Path
• Creating Chimeras
• Confronting Human Chimerism
• Cells, Frozen in Time
• EvMed Edits
• Stories in Other Languages
• Virtual Reality
• Zoom Gallery
• Ugly Bug Galleries
• Ask a Question
• Top Questions
• Question Guidelines
• Permissions
• Information Collected
• Author and Artist Notes
• Share Ask A Biologist
• Articles & News
• Our Volunteers
• Teacher Toolbox

show/hide words to know

ATP: adenosine triphosphate. ATP is the energy-carrying molecule of all cells...... more

Cellulose: the structural material found in the cell wall in most plants. Cellulose is used to make many products, including paper and cloth...  more

Electron transport chain: cell process that uses electrons to generate chemical energy...  more

Ion: an atom or molecule that does not have the same number of electrons as it has protons. This gives the atom or molecule a negative or positive charge...  more

Light-dependent reaction: the first part of photosynthesis where (sun)light energy is captured and stored by a plant...  more

Molecule: a chemical structure that has two or more atoms held together by a chemical bond. Water is a molecule of two hydrogen atoms and one oxygen atom (H2O)...  more

Protein: a type of molecule found in the cells of living things, made up of special building blocks called amino acids.

Starch: made by all green plants and used to store energy for later use...  more

Thylakoid: the disk-shaped parts of a plant cell where light-dependent reactions occur...  more

In with One Energy and out with Another

The light-dependent reactions take place in the thylakoid membrane, inside chloroplasts. Since they are light 'dependent' reactions, you can guess that these reactions need light to work. Remember that the purpose of this first part of photosynthesis is to convert sunlight energy into other forms of energy?

The light-dependent reactions of photosynthesis require sunlight. Image by Mell27.

Plants cannot use light energy directly to make sugars. Instead, the plant changes the light energy into a form it can use: chemical energy. Chemical energy is all around us. For example, cars need the chemical energy from gasoline to run. The chemical energy that plants use are stored in ATP and NADPH. ATP and NADPH are two kinds of energy-carrying molecules. These two molecules are not only in plants, as animals use them as well.

A Recipe for Energy

Plants need water to make NADPH. This water is broken apart to release electrons (negatively charged subatomic particles). When water is broken it also creates oxygen, a gas that we all breathe.

The electrons must travel through special proteins stuck in the thylakoid membrane. They go through the first special protein (the photosystem II protein) and down the electron transport chain. Then they pass through a second special protein (photosystem I protein).

Photosystem I and Photosystem II

Wait a second... first electrons go through the second photosystem and second they go through the first? That seems really confusing. Why would they name the photosystems that way?

Water molecules are broken down to release electrons. These electrons then move down a gradient, storing energy in ATP in the process. Image by Jina Lee.

Photosystem I and II don't align with the route electrons take through the transport chain because they weren't discovered in that order. Photosystem I was discovered first. Later, photosystem II was discovered and found to be earlier in the electron transport chain. But it was too late, the name stuck. Electrons first travel through photosystem II and then photosystem I.

The Electron Transport Chain

While at photosystem II and I, the electrons gather energy from sunlight. How do they do that? Chlorophyll, which is present in the photosystems, soaks up light energy. The energized electrons are then used to make NADPH. The electron transport chain is a series of molecules that accept or donate electrons easily. By moving step-by-step through these, electrons are moved in a specific direction across a membrane. The movement of hydrogen ions are coupled with this. This means that when electrons are moved, hydrogen ions move too. ATP is created when hydrogen ions are pumped into the inner space (lumen) of the thylakoid. Hydrogen ions have a positive charge. Like in magnets, the same charges repel, so the hydrogen ions want to get away from each other. They escape the thylakoid through a membrane protein called ATP synthase. By moving through the protein they give it power, like water moving through a dam. When hydrogen ions move through the protein and down the electron transport chain, ATP is created. This is how plants turn to sunlight into chemical energy that they can use.

The Calvin Cycle: Building Life from Thin Air

How does something like air become the wood of a tree? The answer lies in what makes up the air.

How can the air surrounding a tree be turned into tree material? Through a complex set of reactions that use the carbon from the air to make other materials. Image by André Karwath.

The air holds different elements like oxygen, carbon, and nitrogen. These elements make up molecules like carbon dioxide (CO2). Carbon dioxide is made out of one carbon atom and two oxygen atoms. Plants take the carbon atom from carbon dioxide and use it to build sugars. This is done using the Calvin cycle. The Calvin cycle occurs inside chloroplasts, but outside the thylakoids (where ATP was created). The ATP and NADPH from the light-dependent reactions are used in the Calvin cycle. Parts of the Calvin cycle are sometimes called light-independent reactions. But don't let the name fool you... those reactions do require sunlight to work. The protein RuBisCO also helps in the process to change carbon from the air into sugars. RuBisCO works slowly, so plants need a lot of it. In fact, RuBisCO is the most abundant protein in the world! The products of the Calvin cycle are used to make the simple sugar glucose. Glucose is used to build more complex sugars like starch and cellulose. Starch stores energy for the plant and cellulose is the stuff of which plants are made.

Images via Wikimedia Commons. Seedling image by Bff.

Read more about: Snacking on Sunlight

View citation, bibliographic details:.

• Article: Photosynthesis
• Author(s): Heather Kropp, Angela Halasey
• Publisher: Arizona State University School of Life Sciences Ask A Biologist
• Site name: ASU - Ask A Biologist
• Date published: May 25, 2017
• Date accessed: August 8, 2024
• Link: https://askabiologist.asu.edu/photosynthesis

Heather Kropp, Angela Halasey. (2017, May 25). Photosynthesis. ASU - Ask A Biologist. Retrieved August 8, 2024 from https://askabiologist.asu.edu/photosynthesis

Chicago Manual of Style

Heather Kropp, Angela Halasey. "Photosynthesis". ASU - Ask A Biologist. 25 May, 2017. https://askabiologist.asu.edu/photosynthesis

MLA 2017 Style

Heather Kropp, Angela Halasey. "Photosynthesis". ASU - Ask A Biologist. 25 May 2017. ASU - Ask A Biologist, Web. 8 Aug 2024. https://askabiologist.asu.edu/photosynthesis

Plants need chemical energy to grow and survive. But how do they convert energy in sunlight into chemical energy?

Snacking on Sunlight

Be Part of Ask A Biologist

By volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteers page to get the process started.

Share to Google Classroom

Sciencing_Icons_Science SCIENCE

Sciencing_icons_biology biology, sciencing_icons_cells cells, sciencing_icons_molecular molecular, sciencing_icons_microorganisms microorganisms, sciencing_icons_genetics genetics, sciencing_icons_human body human body, sciencing_icons_ecology ecology, sciencing_icons_chemistry chemistry, sciencing_icons_atomic & molecular structure atomic & molecular structure, sciencing_icons_bonds bonds, sciencing_icons_reactions reactions, sciencing_icons_stoichiometry stoichiometry, sciencing_icons_solutions solutions, sciencing_icons_acids & bases acids & bases, sciencing_icons_thermodynamics thermodynamics, sciencing_icons_organic chemistry organic chemistry, sciencing_icons_physics physics, sciencing_icons_fundamentals-physics fundamentals, sciencing_icons_electronics electronics, sciencing_icons_waves waves, sciencing_icons_energy energy, sciencing_icons_fluid fluid, sciencing_icons_astronomy astronomy, sciencing_icons_geology geology, sciencing_icons_fundamentals-geology fundamentals, sciencing_icons_minerals & rocks minerals & rocks, sciencing_icons_earth scructure earth structure, sciencing_icons_fossils fossils, sciencing_icons_natural disasters natural disasters, sciencing_icons_nature nature, sciencing_icons_ecosystems ecosystems, sciencing_icons_environment environment, sciencing_icons_insects insects, sciencing_icons_plants & mushrooms plants & mushrooms, sciencing_icons_animals animals, sciencing_icons_math math, sciencing_icons_arithmetic arithmetic, sciencing_icons_addition & subtraction addition & subtraction, sciencing_icons_multiplication & division multiplication & division, sciencing_icons_decimals decimals, sciencing_icons_fractions fractions, sciencing_icons_conversions conversions, sciencing_icons_algebra algebra, sciencing_icons_working with units working with units, sciencing_icons_equations & expressions equations & expressions, sciencing_icons_ratios & proportions ratios & proportions, sciencing_icons_inequalities inequalities, sciencing_icons_exponents & logarithms exponents & logarithms, sciencing_icons_factorization factorization, sciencing_icons_functions functions, sciencing_icons_linear equations linear equations, sciencing_icons_graphs graphs, sciencing_icons_quadratics quadratics, sciencing_icons_polynomials polynomials, sciencing_icons_geometry geometry, sciencing_icons_fundamentals-geometry fundamentals, sciencing_icons_cartesian cartesian, sciencing_icons_circles circles, sciencing_icons_solids solids, sciencing_icons_trigonometry trigonometry, sciencing_icons_probability-statistics probability & statistics, sciencing_icons_mean-median-mode mean/median/mode, sciencing_icons_independent-dependent variables independent/dependent variables, sciencing_icons_deviation deviation, sciencing_icons_correlation correlation, sciencing_icons_sampling sampling, sciencing_icons_distributions distributions, sciencing_icons_probability probability, sciencing_icons_calculus calculus, sciencing_icons_differentiation-integration differentiation/integration, sciencing_icons_application application, sciencing_icons_projects projects, sciencing_icons_news news.

• Share Tweet Email Print
• Home ⋅
• Science Fair Project Ideas for Kids, Middle & High School Students ⋅

How Do Plants Store Energy During Photosynthesis?

How Does Photosynthesis Work?

Photosynthesis is the process plants and some algae use to convert light energy to chemical energy stored as sugar within chloroplasts -- the energy factories found in plant cells. Plants need only carbon dioxide and water for photosynthesis to work. Chloroplasts are full of chlorophyll, a green pigment key to photosynthesis, which helps the plant absorb light. Energy stored during photosynthesis begins the flow of energy and carbon down the food chain.

TL;DR (Too Long; Didn't Read)

Once plants convert sunlight into energy, energy molecules help to turn the fuel into sugars in the plant's energy factories called chloroplasts found in the leaves. Through the process of photosynthesis and respiration, plants produce glucose or sugar and oxygen.

Chemical Reaction as a Formula

The formula that describes photosynthesis is 6CO2 + 6H20 + light energy = C6H1206 + 602. What this chemical equation means is that photosynthesis combines light energy with six molecules of carbon dioxide and six molecules of water to produce six molecules of oxygen and one molecule of sugar.

Light Reaction

Photosynthesis is divided into two main stages: light reaction and dark reaction. The light reaction converts light energy into adenosine triphosphate, the energy currency of all life, and Nicotinamide adenine dinucleotide phosphate, both of which become energy-carrier molecules needed for the dark stage or photosynthesis. This step occurs in the thyroidal membrane, a membrane found inside chloroplasts.

Calvin Cycle

The dark reaction employs ATP and NADPH created in the light reaction to transform carbon dioxide into sugar. This phase happens within the plant's stoma in the dark. The main cycle in this stage is called the Calvin cycle, which consists of three stages. Stage one, also called carbon fixation phase, is when carbon dioxide combines with ribulose bisphosphate, a five-carbon sugar. In stage two, ATP helps convert the product of stage one into sugar. The third stage, or regeneration phase, again uses ATP to regenerate the reserve levels of RuBp in the cell, completing the cycle.

Currency of All Life

ATP is an essential component in the process of photosynthesis. Biologists consider it the currency of life, because it is cell's favorite source of energy to do just about anything, from moving muscles to enabling respiration.

Light Absorption

Plants use light energy to start the photosynthesis process and fuel the storage of energy in sugars. Light is divided into various colors with their characteristic wavelengths with each wavelength represented by an individual pigment. Chlorophyll, a specific plant pigment, takes in blue and red light while carotenoid, another type of plant pigment, utilizes blue-green light waves. Green wavelengths are not absorbed efficiently by plants and is reflected by the plant's leaves and stems, which makes plants appear green.

Related Articles

What provides electrons for the light reactions, what is the sun's role in photosynthesis, when does respiration occur in plants, phases of photosynthesis & its location, key differences between c3, c4 and cam photosynthesis, cellular respiration in plants, the three stages of photosynthesis, describe what a photosystem does for photosynthesis, 10 facts on photosynthesis, why do plants need the sun, definition of plant respiration, how does a plant convert light energy to chemical energy, what is produced as a result of photosynthesis, materials needed for photosynthesis, organelles involved in photosynthesis, sequence stages in photosynthesis, how oxygen gas is produced during photosynthesis, what are light dependent reactions, what is nadph in photosynthesis.

• University of California Santa Barbara: How are Photosynthesis and Respiration Related
• University of Michigan: A Primer on Photosynthesis and the Functioning of Cells

About the Author

Andrew Latham is a seasoned copywriter for both print and online publishers. He has a Bachelor of Science, majoring in English, a diploma in linguistics and a special interest in finance, science, languages and travel. He is the owner of LanguageVox.com, a company based in Charlottesville, Virginia, which provides writing, interpreting and translating services for English and Spanish audiences.

Find Your Next Great Science Fair Project! GO

What Are the Products of Photosynthesis?

Result of Photosynthesis in Plants

• Biochemistry
• Chemical Laws
• Periodic Table
• Projects & Experiments
• Scientific Method
• Physical Chemistry
• Medical Chemistry
• Chemistry In Everyday Life
• Famous Chemists
• Activities for Kids
• Abbreviations & Acronyms
• Weather & Climate
• Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
• B.A., Physics and Mathematics, Hastings College

What are the products of photosynthesis? First, let's define this process: Photosynthesis is the name given to the set of chemical reactions performed by plants to convert energy from the sun into chemical energy in the form of sugar. Specifically, plants use energy from sunlight to react to carbon dioxide and water to produce sugar (glucose) and oxygen, the products of photosynthesis.

Many reactions occur, but the overall chemical reaction for photosynthesis is:

• 6 CO 2 + 6 H 2 O + light → C 6 H 12 O 6 + 6 O 2
• Carbon Dioxide + Water + Light yields Glucose + Oxygen

In a plant, the carbon dioxide enters via leaf stomates by diffusion. Water is absorbed through the roots and is transported to leaves through the xylem. Solar energy is absorbed by chlorophyll in the leaves. The reactions of photosynthesis occur in the chloroplasts of plants. In photosynthetic bacteria, the process takes place where chlorophyll or a related pigment is embedded in the plasma membrane. The oxygen and water produced in photosynthesis exit through the stomata.

Key Takeaways

• In photosynthesis, energy from light is used to convert carbon dioxide and water into glucose and oxygen.
• For 6 carbon dioxide and 6 water molecules, 1 glucose molecule and 6 oxygen molecules are produced.

Actually, plants reserve very little of the glucose for immediate use. Glucose molecules are combined by dehydration synthesis to form cellulose, which is used as a structural material. Dehydration synthesis is also used to convert glucose to starch, which plants use to store energy.

Intermediate Products of Photosynthesis

The overall chemical equation is a summary of a series of chemical reactions. These reactions occur in two stages. The light reactions require light (as you might imagine), while the dark reactions are controlled by enzymes. They don't require darkness to occur—they simply don't depend on light.

The light reactions absorb light and harness the energy to power electron transfers. Most photosynthetic organisms capture visible light, although there are some that use infrared light. Products of photosynthesis are adenosine triphosphate ( ATP ) and reduced nicotinamide adenine dinucleotide phosphate (NADPH). In plant cells, the light-dependent reactions occur in the chloroplast thylakoid membrane. The overall reaction for the light-dependent reactions is:

• 2 H 2 O + 2 NADP +  + 3 ADP + 3 P i  + light → 2 NADPH + 2 H +  + 3 ATP + O 2

In the dark stage, ATP and NADPH ultimately reduce carbon dioxide and other molecules. Carbon dioxide from the air is "fixed" into a biologically usable form, glucose . In plants, algae, and cyanobacteria, the dark reactions are termed the Calvin cycle. Bacteria may use different reactions, including a reverse Krebs cycle . The overall reaction for the light-independent reaction of a plant (Calvin cycle) is:

• 3 CO 2  + 9 ATP + 6 NADPH + 6 H +  → C 3 H 6 O 3 -phosphate + 9 ADP + 8 P i  + 6 NADP +  + 3 H 2 O

During carbon fixation, the three-carbon product of the Calvin cycle is converted into the final carbohydrate product.

Factors That Affect the Rate of Photosynthesis

Like any chemical reaction, the availability of the reactants determines the amount of products of photosynthesis that can be made. Limiting the availability of carbon dioxide or water slows the production of glucose and oxygen . Also, the rate of the reactions is affected by temperature and the availability of minerals that may be needed in the intermediate reactions.

The overall health of the plant (or other photosynthetic organism) also plays a role. The rate of metabolic reactions is determined in part by the maturity of the organism and whether it's flowering or bearing fruit.

What Is Not a Product of Photosynthesis?

If you're asked about this process on a test, you may be asked to identify the products of photosynthesis . That's pretty easy, right? Another form of the question is to ask what is not a product of photosynthesis. Unfortunately, this won't be an open-ended question, which you could easily answer with "iron" or "a car" or "your mom." Usually this is a multiple choice question, listing molecules which are reactants or products of photosynthesis. The answer is any choice except glucose or oxygen. The question may also be phrased to answer what is not a product of the light reactions or the dark reactions. So, it's a good idea to know the overall reactants and products for the photosynthesis general equation, the light reactions, and the dark reactions.

• Bidlack, J.E.; Stern, K.R.; Jansky, S. (2003). Introductory Plant Biology . New York: McGraw-Hill. ISBN 978-0-07-290941-8.
• Blankenship, R.E. (2014). Molecular Mechanisms of Photosynthesis (2nd ed.). John Wiley & Sons. ISBN 978-1-4051-8975-0.
• Reece J.B., et al. (2013). Campbell Biology . Benjamin Cummings. ISBN 978-0-321-77565-8.
• What Is the Primary Function of the Calvin Cycle?
• The Differences Between DNA and RNA
• How to Calculate Molarity of a Solution
• Photosynthesis Vocabulary Terms and Definitions
• 10 Fascinating Photosynthesis Facts
• Chlorophyll Definition and Role in Photosynthesis
• Calvin Cycle Steps and Diagram
• Chemosynthesis Definition and Examples
• What Is Fermentation? Definition and Examples
• The Balanced Chemical Equation for Photosynthesis
• What Is the Most Abundant Protein?
• Societal Concerns with Biotechnology
• The Definition of Bioenergy
• Equilibrium Constant Kc and How to Calculate It
• Chemical Equilibrium in Chemical Reactions
• Food and Other Products Formed By Fermentation

Overview of Photosynthesis

Please log in to save materials. Log in

• EPUB 3 Student View
• PDF Student View
• Thin Common Cartridge
• Thin Common Cartridge Student View
• SCORM Package
• SCORM Package Student View
• 2 - Main Structures and Summary of Photosynthesis
• 3 - Basic Photosynthetic Structures
• 4 - The Two Parts of Photosynthesis
• 5 - Section Summary
• 6 - Art Connections
• 7 - Review Questions
• 8 - Free Response
• View all as one page

Photosynthesis is essential to all life on earth; both plants and animals depend on it. It is the only biological process that can capture energy that originates from sunlight and converts it into chemical compounds (carbohydrates) that every organism uses to power its metabolism. It is also a source of oxygen necessary for many living organisms. In brief, the energy of sunlight is “captured” to energize electrons, whose energy is then stored in the covalent bonds of sugar molecules. How long lasting and stable are those covalent bonds? The energy extracted today by the burning of coal and petroleum products represents sunlight energy captured and stored by photosynthesis 350 to 200 million years ago during the Carboniferous Period.

Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis ( Figure ). Because they use light to manufacture their own food, they are called photoautotrophs (literally, “self-feeders using light”). Other organisms, such as animals, fungi, and most other bacteria, are termed heterotrophs (“other feeders”), because they must rely on the sugars produced by photosynthetic organisms for their energy needs. A third very interesting group of bacteria synthesize sugars, not by using sunlight’s energy, but by extracting energy from inorganic chemical compounds. For this reason, they are referred to as chemoautotrophs .

The importance of photosynthesis is not just that it can capture sunlight’s energy. After all, a lizard sunning itself on a cold day can use the sun’s energy to warm up in a process called behavioral thermoregulation . In contrast, photosynthesis is vital because it evolved as a way to store the energy from solar radiation (the “photo-” part) to energy in the carbon-carbon bonds of carbohydrate molecules (the “-synthesis” part). Those carbohydrates are the energy source that heterotrophs use to power the synthesis of ATP via respiration. Therefore, photosynthesis powers 99 percent of Earth’s ecosystems. When a top predator, such as a wolf, preys on a deer ( Figure ), the wolf is at the end of an energy path that went from nuclear reactions on the surface of the sun, to visible light, to photosynthesis, to vegetation, to deer, and finally to the wolf.

Main Structures and Summary of Photosynthesis

Photosynthesis is a multi-step process that requires specific wavelengths of visible sunlight, carbon dioxide (which is low in energy), and water as substrates ( Figure ). After the process is complete, it releases oxygen and produces glyceraldehyde-3-phosphate (GA3P), as well as simple carbohydrate molecules (high in energy) that can then be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy and the energized carbon that all living things need to survive.

The following is the chemical equation for photosynthesis ( Figure ):

Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the structures involved.

Basic Photosynthetic Structures

In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells. The process of photosynthesis occurs in a middle layer called the mesophyll . The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata (singular: stoma), which also play roles in the regulation of gas exchange and water balance. The stomata are typically located on the underside of the leaf, which helps to minimize water loss due to high temperatures on the upper surface of the leaf. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes.

In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast . For plants, chloroplast-containing cells exist mostly in the mesophyll. Chloroplasts have a double membrane envelope (composed of an outer membrane and an inner membrane), and are ancestrally derived from ancient free-living cyanobacteria. Within the chloroplast are stacked, disc-shaped structures called thylakoids . Embedded in the thylakoid membrane is chlorophyll, a pigment (molecule that absorbs light) responsible for the initial interaction between light and plant material, and numerous proteins that make up the electron transport chain. The thylakoid membrane encloses an internal space called the thylakoid lumen . As shown in Figure , a stack of thylakoids is called a granum , and the liquid-filled space surrounding the granum is called stroma or “bed” (not to be confused with stoma or “mouth,” an opening on the leaf epidermis).

Art Connection

On a hot, dry day, the guard cells of plants close their stomata to conserve water. What impact will this have on photosynthesis?

The Two Parts of Photosynthesis

Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light-independent reactions. In the light-dependent reactions , energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy. In the light-independent reactions , the chemical energy harvested during the light-dependent reactions drives the assembly of sugar molecules from carbon dioxide. Therefore, although the light-independent reactions do not use light as a reactant, they require the products of the light-dependent reactions to function. In addition, however, several enzymes of the light-independent reactions are activated by light. The light-dependent reactions utilize certain molecules to temporarily store the energy: These are referred to as energy carriers . The energy carriers that move energy from light-dependent reactions to light-independent reactions can be thought of as “full” because they are rich in energy. After the energy is released, the “empty” energy carriers return to the light-dependent reaction to obtain more energy. Figure illustrates the components inside the chloroplast where the light-dependent and light-independent reactions take place.

Link to Learning

Click the link to learn more about photosynthesis.

Everyday Connection

Photosynthesis at the Grocery Store

Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle ( Figure ) contains hundreds, if not thousands, of different products for customers to buy and consume.

Although there is a large variety, each item ultimately can be linked back to photosynthesis. Meats and dairy link, because the animals were fed plant-based foods. The breads, cereals, and pastas come largely from starchy grains, which are the seeds of photosynthesis-dependent plants. What about desserts and drinks? All of these products contain sugar—sucrose is a plant product, a disaccharide, a carbohydrate molecule, which is built directly from photosynthesis. Moreover, many items are less obviously derived from plants: For instance, paper goods are generally plant products, and many plastics (abundant as products and packaging) are derived from “algae” (unicellular plant-like organisms, and cyanobacteria). Virtually every spice and flavoring in the spice aisle was produced by a plant as a leaf, root, bark, flower, fruit, or stem. Ultimately, photosynthesis connects to every meal and every food a person consumes.

Section Summary

The process of photosynthesis transformed life on Earth. By harnessing energy from the sun, the evolution of photosynthesis allowed living things access to enormous amounts of energy. Because of photosynthesis, living things gained access to sufficient energy that allowed them to build new structures and achieve the biodiversity evident today.

Only certain organisms (photoautotrophs), can perform photosynthesis; they require the presence of chlorophyll, a specialized pigment that absorbs certain wavelengths of the visible spectrum and can capture energy from sunlight. Photosynthesis uses carbon dioxide and water to assemble carbohydrate molecules and release oxygen as a byproduct into the atmosphere. Eukaryotic autotrophs, such as plants and algae, have organelles called chloroplasts in which photosynthesis takes place, and starch accumulates. In prokaryotes, such as cyanobacteria, the process is less localized and occurs within folded membranes, extensions of the plasma membrane, and in the cytoplasm.

Art Connections

Figure On a hot, dry day, plants close their stomata to conserve water. What impact will this have on photosynthesis?

Figure Levels of carbon dioxide (a necessary photosynthetic substrate) will immediately fall. As a result, the rate of photosynthesis will be inhibited.

Review Questions

Which of the following components is not used by both plants and cyanobacteria to carry out photosynthesis?

• chloroplasts
• chlorophyll
• carbon dioxide

What two main products result from photosynthesis?

• oxygen and carbon dioxide
• chlorophyll and oxygen
• sugars/carbohydrates and oxygen
• sugars/carbohydrates and carbon dioxide

In which compartment of the plant cell do the light-independent reactions of photosynthesis take place?

• outer membrane

Which statement about thylakoids in eukaryotes is not correct?

• Thylakoids are assembled into stacks.
• Thylakoids exist as a maze of folded membranes.
• The space surrounding thylakoids is called stroma.
• Thylakoids contain chlorophyll.

Predict the end result if a chloroplast’s light-independent enzymes developed a mutation that prevented them from activating in response to light.

• GA3P accumulation
• ATP and NADPH accumulation
• Water accumulation
• Carbon dioxide depletion

How are the NADPH and GA3P molecules made during photosynthesis similar?

• They are both end products of photosynthesis.
• They are both substrates for photosynthesis.
• They are both produced from carbon dioxide.
• They both store energy in chemical bonds.

Free Response

What is the overall outcome of the light reactions in photosynthesis?

The outcome of light reactions in photosynthesis is the conversion of solar energy into chemical energy that the chloroplasts can use to do work (mostly anabolic production of carbohydrates from carbon dioxide).

Why are carnivores, such as lions, dependent on photosynthesis to survive?

Because lions eat animals that eat plants.

Why are energy carriers thought of as either “full” or “empty”?

The energy carriers that move from the light-dependent reaction to the light-independent one are “full” because they bring energy. After the energy is released, the “empty” energy carriers return to the light-dependent reaction to obtain more energy. There is not much actual movement involved. Both ATP and NADPH are produced in the stroma where they are also used and reconverted into ADP, Pi, and NADP + .

Describe how the grey wolf population would be impacted by a volcanic eruption that spewed a dense ash cloud that blocked sunlight in a section of Yellowstone National Park.

The grey wolves are apex predators in their food web, meaning they consume smaller prey animals and are not the prey of any other animal. Blocking sunlight would prevent the plants at the bottom of the food web from performing photosynthesis. This would kill many of the plants, reducing the food sources available to smaller animals in Yellowstone. A smaller prey animal population means that fewer wolves can survive in the area, and the population of grey wolves will decrease.

How does the closing of the stomata limit photosynthesis?

The stomata regulate the exchange of gases and water vapor between a leaf and its surrounding environment. When the stomata are closed, the water molecules cannot escape the leaf, but the leaf also cannot acquire new carbon dioxide molecules from the environment. This limits the light-independent reactions to only continuing until the carbon dioxide stores in the leaf are depleted.

You are using an outdated browser. Please upgrade your browser or activate Google Chrome Frame to improve your experience.

• Account Home

Activities and Experiments to Explore Photosynthesis in the Classroom

Photosynthesis can be a difficult concept to grasp, that’s why we’ve compiled a selection of hands-on activities and experiments to help show students some of the concepts in action.

In addition to the ideas below, PLT’s new Explore Your Environment: K-8 Activity Guide and PLT’s PreK-8 Environmental Education Activity Guide both offer a wealth of hands-on, creative activities and resources for lessons about photosynthesis. Each guide includes a comprehensive Topic Index to help you quickly find a list of relevant activities that fit your needs and every activity includes a background section for educators that gives a science-based introduction to the activity’s content. We also have a few abridged versions related to the physiology of trees and photosynthesis for families to try out together at home, for example, How Plants Grow and Tree Factory .

Introduction to Photosynthesis

The word “photosynthesis” comes from Greek root words that combine to mean “to put together with the help of light.”

All plants, algae, and some microorganisms like bacteria photosynthesize to make their own food. This makes them part of a group of organisms called autotrophs. Unlike heterotrophs, which include animals that feed off other living organisms, autotrophs make nutritional organic substances from simple inorganic substances. What a superpower!

To undergo photosynthesis, plants need carbon dioxide from the air, water from the soil, and sunlight. These elements combine in a chemical reaction that takes place inside of a plant’s leaves to create glucose and oxygen.

Absorbing Carbon Dioxide and Water

Carbon dioxide can be produced naturally from the decomposition of living things and events like volcanic eruptions, and from human activity like burning fossil fuels.

Animals respirate by inhaling gases in the air, retaining oxygen, and releasing carbon dioxide. However, when plants breathe, they take in carbon dioxide, which is a key ingredient required for photosynthesis. Carbon dioxide enters a plant through its stomata, tiny pores that are usually located on the underside of leaves and sometimes stems. Most plants also soak up another substance through their roots that they need for photosynthesis: water.

Adding Energy

Once a plant has carbon dioxide and water, it needs energy to enable these two substances to chemically react with each other. It gets energy from a steady stream of sunlight hitting its leaves. Chlorophyll, a green pigment found in tiny structures called chloroplasts within leaves, absorbs energy from blue and red light waves from the sun. The sunlight’s energy is then transferred to two types of energy-storing molecules within the plant.

The energy already stored from the sun fuels a reaction in the leaves’ chloroplasts that splits water molecules (H 2 0) into pure hydrogen (H) and oxygen (O 2 ). The hydrogen reacts with carbon dioxide (CO 2 ) to produce glucose, a type of sugar. The full chemical equation of photosynthesis looks like this:

6CO 2 + 6H 2 0 + Sunlight → C 6 H 12 O 6 + 6O 2

In other words, the carbon dioxide and water that go into the plant combine with energy from sunlight to produce glucose, and also oxygen.

Storing and Using Glucose

Once this sugar is made, it can be stored as energy (food) that the plant uses for growth and repair. Plants also use the energy from nutrients in the soil along with glucose to grow and develop leaves, flowers, and fruits.

Students often wonder how a gas like carbon dioxide that you can’t see helps form a giant tree or the apple they eat for lunch. It’s because a chemical reaction doesn’t have to start with a solid (like soil) to end with a solid (like a tree or apple). It helps for students to understand the carbon cycle – and PLT has a variety of content to support this.

Glucose is a carbohydrate, which is simply a molecule containing carbon, hydrogen, and oxygen. Smaller glucose molecules can build bigger carbohydrates like cellulose or starch.

Similar to a human skeleton, cellulose is the main component of plant cell walls that help strengthen the plant. Humans can’t digest cellulose, but the fiber found in cellulose-heavy foods like celery and broccoli aids with digestion and can lower the risk of diseases like cancer. These strong fibers are also used to make clothes and paper. Animals like cows, horses, and sheep can digest cellulose, so it makes sense that they eat grass for quick energy and nutrients.

Plants can also convert glucose into starch, which is a larger carbohydrate molecule that can store its energy. Humans break down starches found in foods like potatoes and rice into glucose, and it, in turn, gives them energy.

Though you may not use sunlight to create your food, when you eat something like chicken or rice, you take in energy plants used from the sun. And not only does a plant produce food animals need for their energy as a result of photosynthesis, but it also releases oxygen as a byproduct through its stomata into the atmosphere.

Photosynthesis is critical for the survival of all living organisms — not just plants.

Hands-On Photosynthesis Activities

Photosynthesis can be a difficult concept to grasp, especially for younger learners. That’s why we’ve compiled these interactive activities and experiments that show some of the concepts in action.

Photosynthesis Visuals

These photosynthesis modeling activities will help students visualize and better understand what a plant needs to undergo photosynthesis and what it produces as a result. The 3D and 2D representations will also help them absorb some of the vocabulary associated with photosynthesis.

3D Photosynthesis: Tree Leaf Model 

Older students can create these more complex 3D models of a leaf’s front and backside where all of the photosynthesis action takes place, like on its stomata and chloroplasts. They will attach labels to the leaf that describe the different substances involved.

The Ins and Outs of Photosynthesis

Younger learners will enjoy this less complex visual activity that involves a leaf with “IN” and “OUT” envelopes into which they’ll place the respective chemical reactants or products of photosynthesis.

Photosynthesis Paper Craft  

Take your lesson in an artistic direction by letting students create these bright and fun paper flower and sun displays, complete with the basic photosynthesis terms.

Exploring Leaves with STEM 

These STEM experiments requiring real leaves will spark valuable critical thinking when students observe leaf structure, stomata, plant respiration, and more.

Respirating Leaves

The invisible chemical process of a leaf exchanging carbon dioxide, water, and sunlight for oxygen will become visible when your class observes what happens when they submerge leaves in water.

Stomata Microscope Investigation

Students will use microscopes to explore the structure of a leaf that makes the exchange of gasses during photosynthesis possible. They can also explore other parts of leaves and how plants gain mass.

Stomata Microscope Comparison

Compare the stomata sizes and numbers of different plant species under a microscope and examine leaf texture by creating cool “nail polish imprints.”

Exploring Plants and Sunlight

Plants need sunlight for survival, so it makes sense that their behavior or appearance would change if their access to sunlight is altered. These activities explore this concept.

Measuring Plant Growth with Sunlight 

This activity takes a couple of weeks but will give your students valuable insight into how a plant’s growth and green coloration is affected by varying levels of sunlight over time. They’ll flex their critical thinking skills as they take daily notes and conclude what happens to a seed under different light conditions.

Rotating Plants

Track how plants bend towards the sun wherever they are with this great exercise that introduces young students to just how active plants can be when it comes to gaining precious sun energy. You can grow seedlings or even experiment with a larger plant you have and see how its color or growth is affected when you rotate or move closer or further from the sun.

Fun with Plant Pigmentation 

There’s a lot of fun that can be had with the chlorophyll in leaves, including art and color experimentation! 

Chlorophyll Paintings 

Chlorophyll pigment not only turns plants green – it makes leaves great mediums for “green” art projects! Kids will love this out-of-the-box painting style, learn about chlorophyll firsthand, and expand their creativity all at once.

Leaf Color Chemistry Experiment 

When the school year begins, recreate how leaves change color in autumn with green leaves, rubbing alcohol, coffee filters, and other easy-to-find items. The pigments of chlorophyll will fade and leave behind hidden pigments that demonstrate why leaves change color in the fall – which is also when your class can reflect back on this eye-opening experiment.

Let Project Learning Tree Be Your Guide

Introduce students to photosynthesis with these PLT activities from the new Explore Your Environment: K-8 Activity Guide :

• Here We Grow Again (for grades K-2), Every Tree for Itself , and Signs of Fall (for grades 3-5) in PLT’s Explore Your Environment: K-8 Activity Guide
• How Plants Grow and Sunlight and Shades of Green (Activities 41 and 42 in PLT’s PreK-8 Environmental Education Activity Guide ), and
• Power Plants (Activity 4 in PLT’s Energy & Ecosystems E-Unit).

Watch an example of an activity! This video walks viewers through PLT’s activity Signs of Fall. In this activity, participants are introduced to different leaf pigments and use chromatography to pull out leaf pigments using simple household items. It helps answer the question, “Why do leaves change color?”.

For further guidance on how to relay the essential concepts of photosynthesis to your classroom and more great activities, check out this Unit of Instruction by Project Learning Tree. It suggests linking select PLT activities to help students learn more about the topic of photosynthesis using a storyline technique. Storylines ensure connectivity and continuity between individual activities and can serve as the “instructional glue” that bind many areas of knowledge and skills. The Unit of Instruction includes a guiding question, concepts addressed, and connections to the Next Generation Science Standards (NGSS) and PLT’s Forest Literacy Framework.

To boost your teaching with 50 field-tested, hands-on multidisciplinary activities that educate and connect elementary students with nature in powerful ways, and more suggested Units of Instruction , look no further than Project Learning Tree’s new Explore Your Environment: K-8 Activity Guide .

Rebecca Reynandez

Leave a reply cancel reply.

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

Save my name, email, and website in this browser for the next time I comment.

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

Easy Plant Science Experiments for the Classroom

Looking for inexpensive and interactive STEM activities for your classroom? Conducting science experiments with plants is an easy way to incorporate hands-on experiences to your curriculum.

Environmental Education Resources

Every month we carefully select new educational apps, videos, interactive websites, books, careers information, and teacher-generated materials that support PLT lessons.

STEM: Water Wonders

World Oceans Day (June 8) is the perfect time to explore the water cycle. Take PLT’s Water Wonders activity a step further with these STEM-focused ideas. Students will learn more about the importance of water conservation, how we use and engineer water, and they’ll discover some water-focused careers.

PreK-8 Environmental Education Activity Guide – Activity 51, Make Your Own Paper

Students investigate the papermaking process by trying it themselves. Students are thrilled to find that they can make paper and that their product is practical, as well as beautiful. Watch a video of the paper-making process used in this activity.

MAKE LEARNING FUN

ATTEND A TRAINING

Get our educational materials and professional development by participating in an in-person workshop or an online course.

CONTACT YOUR COORDINATOR

Get information relevant to your state, plus local assistance and connections to resources and professionals in your community.

EDUCATOR TIPS

Get a wealth of up-to-date resources, support, and ideas from teachers and other educators.

SUBSCRIBE TO OUR NEWSLETTER,  The Branch

Sign up for our monthly e-newsletter for free tools and resources, new lesson plans, professional development and grant opportunities, and tips from educators for teaching about the environment.

• Email Address *
• First Name * First

If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

To log in and use all the features of Khan Academy, please enable JavaScript in your browser.

AP®︎/College Biology

Course: ap®︎/college biology   >   unit 3.

• Photosynthesis
• Intro to photosynthesis
• Breaking down photosynthesis stages
• Conceptual overview of light dependent reactions

The light-dependent reactions

• The Calvin cycle
• Photosynthesis evolution
• Photosynthesis review

Introduction

• Plants carry out a form of photosynthesis called oxygenic photosynthesis . In oxygenic photosynthesis, water molecules are split to provide a source of electrons for the electron transport chain, and oxygen gas is released as a byproduct. Plants organize their photosynthetic pigments into two separate complexes called photosystems (photosystems I and II), and they use chlorophylls as their reaction center pigments.
• Purple sulfur bacteria, in contrast, carry out anoxygenic photosynthesis , meaning that water is not used as an electron source and oxygen gas is not produced. Instead, these bacteria use hydrogen sulfide ( H 2 S ‍   ) as an electron source and produce elemental sulfur as a byproduct. In addition, purple sulfur bacteria have only one photosystem, and they use chlorophyll-like molecules called bacteriochlorophylls as reaction center pigments 1 , 2 , 3 ‍   .

Overview of the light-dependent reactions

• Light absorption in PSII. When light is absorbed by one of the many pigments in photosystem II, energy is passed inward from pigment to pigment until it reaches the reaction center. There, energy is transferred to P680, boosting an electron to a high energy level. The high-energy electron is passed to an acceptor molecule and replaced with an electron from water. This splitting of water releases the O 2 ‍   we breathe.
• ATP synthesis. The high-energy electron travels down an electron transport chain, losing energy as it goes. Some of the released energy drives pumping of H + ‍   ions from the stroma into the thylakoid interior, building a gradient. ( H + ‍   ions from the splitting of water also add to the gradient.) As H + ‍   ions flow down their gradient and into the stroma, they pass through ATP synthase, driving ATP production in a process known as chemiosmosis .
• Light absorption in PSI. The electron arrives at photosystem I and joins the P700 special pair of chlorophylls in the reaction center. When light energy is absorbed by pigments and passed inward to the reaction center, the electron in P700 is boosted to a very high energy level and transferred to an acceptor molecule. The special pair's missing electron is replaced by a new electron from PSII (arriving via the electron transport chain).
• NADPH formation. The high-energy electron travels down a short second leg of the electron transport chain. At the end of the chain, the electron is passed to NADP + ‍   (along with a second electron from the same pathway) to make NADPH.

What is a photosystem?

Photosystem i vs. photosystem ii.

• Special pairs. The chlorophyll a special pairs of the two photosystems absorb different wavelengths of light. The PSII special pair absorbs best at 680 nm, while the PSI special absorbs best at 700 nm. Because of this, the special pairs are called P680 and P700 , respectively.
• Primary acceptor . The special pair of each photosystem passes electrons to a different primary acceptor. The primary electron acceptor of PSII is pheophytin, an organic molecule that resembles chlorophyll, while the primary electron acceptor of PSI is a chlorophyll called A 0 ‍   7 , 8 ‍   .
• Source of electrons . Once an electron is lost, each photosystem is replenished by electrons from a different source. The PSII reaction center gets electrons from water, while the PSI reaction center is replenished by electrons that flow down an electron transport chain from PSII.

Photosystem II

Electron transport chains and photosystem i, some electrons flow cyclically, attribution:, works cited:.

• Lodish, H., Berk, A., Zipursky, S. L., Matsudaira, P., Baltimore, D., and Darnell, J. (2000). Molecular analysis of photosystems. In Molecular cell biology (4th ed., section 16.4). New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK21484/ .
• Boundless. (2015, July 21). Anoxygenic photosynthetic bacteria. In Boundless microbiology . Retrieved from https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/microbial-evolution-phylogeny-and-diversity-8/nonproteobacteria-gram-negative-bacteria-105/anoxygenic-photosynthetic-bacteria-551-7338/ .
• Purple sulfur bacteria. (2015, July 16). Retrieved October 24, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Purple_sulfur_bacteria .
• Soda lake. (2015, September 26). Retrieved October 24, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Soda_lake .
• Gutierrez, R. Bio41 Week 7 Biochemistry Lectures 11 and 12. Bio41. 2009.
• Berg, J. M., Tymoczko, J. L., and Stryer, L. (2002). Accessory pigments funnel energy into reaction centers. In Biochemistry (5th ed., section 19.5). New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK22604/ .
• Pheophytin. (2015, February 11). Retrieved October 28, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Pheophytin .
• Photosystem I. (2016, June 25). Retrieved from Wikipedia on July 22, 2016: https://en.wikipedia.org/wiki/Photosystem_I .
• Berg, J. M., Tymoczko, J. L., and Stryer, L. (2002). Two photosystems generate a proton gradient and NADPH in oxygenic photosynthesis. In Biochemistry (5th ed., section 19.3). New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK22538/#_A2681_ .
• Joliot, P. and Johnson, G. N. (2011). Regulation of cyclic and linear electron flow in higher plants. PNAS, 108(32), 13317-13322. http://dx.doi.org/10.1073/pnas.1110189108 .
• Johnson, Giles N. (2011). Physiology of PSI cyclic electron transport in higher plants. Biochimica et Biophysica Acta - Bioenergetics , 1807 (8), 906-911. http://dx.doi.org/doi:10.1016/j.bbabio.2010.11.009 .
• Berg, J. M., Tymoczko, J. L., and Stryer, L. (2002). A proton gradient across the thylakoid membrane drives ATP synthesis. In Biochemistry (5th ed., section 19.4). New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK22519/ .
• Takahashi, S., Milward, S. E., Fan, D.-Y., Chow, W. S., and Badger, M. R. (2008). How does cyclic electron flow alleviate photoinhibition in Arabidopsis? Plant Physiology , 149 (3), 1560-1567. http://dx.doi.org/10.1104/pp.108.134122 .

Additional references:

Want to join the conversation.

• Upvote Button navigates to signup page
• Downvote Button navigates to signup page
• Flag Button navigates to signup page

Plants' Oxygen-Giving Superpower: A Simple Experiment

• Last updated Aug 21, 2024
• Difficulty Advanced

• Category Advanced gardening

Plants are crucial to human and animal survival as they are the primary source of energy. Through the process of photosynthesis, plants use carbon dioxide, water, and sunlight to create glucose and oxygen. This process is essential for maintaining the oxygen levels necessary for life on Earth.

A simple experiment to demonstrate how plants give off oxygen involves submerging a leaf in water and placing it in sunlight. Over time, tiny bubbles form on the leaf's surface, which can be observed with the naked eye or a magnifying glass. These bubbles are oxygen, released by the leaf through photosynthesis.

What You'll Learn

• How plants create oxygen through photosynthesis?

The role of light in photosynthesis

• How to observe photosynthesis?

The difference between plant and animal respiration

The importance of plants for human and animal survival.

How plants create oxygen through photosynthesis

Plants, like all living things, need food to survive. However, unlike animals, plants can make their own food through a process called photosynthesis. This process allows plants to use energy from sunlight to convert carbon dioxide and water into glucose and oxygen.

The word "photosynthesis" means "making things with light", and this is exactly what happens during this complex chemical process. Plants take in water (H2O) through their roots and carbon dioxide (CO2) from the air through tiny holes in their leaves, flowers, branches, stems, and roots. These tiny holes are called stomata and are found in the epidermis, or outer tissue layer, of the plant. The photons in sunlight provide the energy required for photosynthesis to occur, and the plant captures these photons with light-absorbing pigments such as chlorophyll and carotenoids.

Once the plant has absorbed water and carbon dioxide, the water is oxidised, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose. The plant then releases the oxygen through the stomata back into the air and stores the energy within the glucose molecules.

The chemical equation for photosynthesis is:

6CO2 + 6H2O + Light energy → C6H12O6 (glucose) + 6O2

This equation shows that for every six molecules of carbon dioxide and water, six molecules of oxygen are produced, along with one molecule of glucose. The glucose is used by the plant as fuel for growth and repair, while the oxygen is released into the atmosphere for animals and aerobic bacteria to breathe.

Plants are autotrophs, which means they produce their own food. The process of photosynthesis is essential for life on Earth, as it not only provides plants with the energy they need to survive but also ensures a constant supply of oxygen in the atmosphere.

Planting the Ethereal Red Spider Lily: A Step-by-Step Guide

You may want to see also

During photosynthesis, light energy is absorbed by chlorophyll, a photosynthetic pigment found in plants. Chlorophyll absorbs blue, red, and violet light rays, with blue light absorption resulting in the highest rate of photosynthesis, followed by red light. Green light, on the other hand, is not absorbed by plants and is reflected, which is why chlorophyll appears green to our eyes.

The intensity of light also plays a significant role in photosynthesis. Higher light intensity leads to an increased rate of photosynthesis, while lower light intensity decreases the rate. This relationship between light intensity and photosynthesis can be observed through simple experiments, such as counting the number of bubbles released by plants during a given period under different light conditions.

In addition to light, other factors such as carbon dioxide concentration, temperature, water availability, and atmospheric pollution also influence the rate of photosynthesis. However, light remains the major driving force behind this process, providing the energy necessary for plants to convert carbon dioxide and water into glucose and release oxygen as a byproduct.

Ground Orchards: Central Florida's Best Planting Spots

How to observe photosynthesis.

Photosynthesis is a process that is critical for the existence of life on Earth. It involves the conversion of light energy into chemical energy, which is stored in the form of organic compounds. To observe photosynthesis, there are a few key methods and techniques that can be employed:

Measuring the Uptake of Carbon Dioxide

One way to observe photosynthesis is by measuring the uptake of carbon dioxide (CO2) by the plant. This can be done using methods such as:

• Using immobilised algae: This technique, known as the 'algal balls' technique, involves using immobilised algae in a hydrogen carbonate indicator solution to measure the rate of photosynthesis and respiration.
• IRGA (Infra-Red Gas Analyser): An IRGA can be used to compare the CO2 concentration in the gas passing into a chamber surrounding a leaf or plant with the CO2 leaving the chamber.
• CO2 monitor: Simply put a plant in a plastic bag and monitor the CO2 concentration in the bag using a CO2 monitor. Alternatively, place some Bicarbonate Indicator Solution in the bag and watch for a colour change.

Measuring the Production of Oxygen

Another method to observe photosynthesis is by measuring the production of oxygen. This can be achieved through techniques such as:

• Counting bubbles: Place Cabomba pondweed in an upside-down syringe in a water bath connected to a capillary tube. Put the weed in a solution of NaHCO3 solution and investigate the amount of gas produced at different distances from a lamp.
• Audus apparatus: Use the Audus apparatus to measure the amount of gas evolved over a period of time.

Measuring the Production of Carbohydrates

Photosynthesis can also be observed by measuring the production of carbohydrates. A crude but simple method is to cut a disc from one side of a leaf, dry and weigh it, then repeat the process with the other half of the leaf some days or weeks later. The increase in mass indicates the extra mass stored in the leaf through photosynthesis.

Measuring the Increase in Dry Mass

The dry mass of plants can be monitored through 'serial harvests', where several plants are harvested, dried, and weighed repeatedly over the duration of the experiment. This provides an accurate measure of surplus photosynthesis by comparing it with the respiration that has taken place.

Investigating the Light-Dependent Reaction

The rate of decolourisation of DCPIP in the Hill Reaction is a measure of the light-requiring stages of photosynthesis. This can be used to investigate the light-dependent reaction in photosynthesis.

Reviving a Dying Dracena Plant

Respiration is a process that enables living organisms to produce energy by taking in oxygen and releasing carbon dioxide. While both plants and animals respire, there are key differences in how this process occurs.

Plant Respiration

Plants do not breathe; they only respire through their leaves, taking in oxygen directly from the air through stomata—small openings in the leaves, stems, and roots. The carbon dioxide produced during plant respiration is used for photosynthesis, which produces glucose and oxygen. Plants can also produce energy through photosynthesis, so they do not rely solely on cellular respiration as animals do. The rate of respiration in plants is slow, and there is little transport of respiratory gases from one part of the plant to another.

Animal Respiration

Animals, on the other hand, breathe air for cellular respiration, taking in oxygen through their nostrils or gills and into their respiratory organs, such as lungs or gills. The carbon dioxide produced during animal respiration is released into the atmosphere and not utilised further. Animals do not photosynthesise, so they must obtain glucose through their diet. The rate of respiration in animals is fast, and respiratory gases are transported over long distances inside the animal.

Additional Differences

Another difference lies in the end products of respiration. One of the end products of plant respiration is ethanol, while one of the end products of animal respiration is lactic acid. Furthermore, plants do not have a respiratory system, and they do not have respiratory pigments to transport oxygen to their cells. Plants also produce less heat during respiration than animals.

Cal Mag Emergency: Saving Your Plants with Calcium and Magnesium

Plants are essential for human and animal survival. They are the primary producers, and all other living organisms on Earth depend on them. There are around three to four lakh identified plant species, and this number is still increasing. Plants provide us with food, air, clothing, wood, medicine, shelter, and many other products that benefit humans.

Plants play a crucial role in maintaining the quality of the atmosphere by releasing oxygen and absorbing carbon dioxide through the process of photosynthesis. They also help maintain the ozone layer, protecting life on Earth from harmful UV radiation. Additionally, plants provide habitat and food for insects, birds, monkeys, and other small animals.

Plants are a significant source of nutrition for humans, providing vegetables, fruits, seeds, oils, beverages, and other food products. They are also used in the production of medicine, with many life-saving drugs derived from roots, herbs, barks, and leaves. Plants are essential for industries, providing raw materials for paper, spices, cosmetics, pencils, rubber, furniture, and household items.

Trees, as the largest plants, are particularly vital to human survival. They supply oxygen, food, and shelter, clean the air, filter water, and provide habitats for a vast number of species. Without plants, life on Earth would not be possible, and it is crucial that we respect and conserve these life-supporting organisms.

Prepare Soil for a Lush Garden

Frequently asked questions.

Plants give off oxygen through the process of photosynthesis. During photosynthesis, plants use sunlight to convert carbon dioxide and water into glucose and oxygen.

One simple experiment to see plants giving off oxygen is to submerge a leaf in water and leave it in a sunny location. After a few hours, small bubbles of oxygen will form around the leaf and at the edges of the bowl.

The air we breathe contains 21% oxygen, which is produced by plants through photosynthesis. Without plants, we would not have enough oxygen to survive.

• Anna Johnston Author Reviewer Gardener

• May Leong Author Editor Reviewer Gardener

It is awesome. Thank you for your feedback!

We are sorry. Plesae let us know what went wrong?

We will update our content. Thank you for your feedback!

Leave a comment

Advanced gardening photos.

Related posts

VOCs: Plants' Chemical Defense

• Jul 08, 2024

Ficus and Spider Plants: Pet-friendly?

• Jul 02, 2024

Planting Baby's Breath: A Guide to Growing This Delicate Beauty

• Jul 18, 2024

Plucking Thyme: Harvesting Nature's Clock

• Aug 02, 2024

Feeding Black Raspberries: Fertilizer Guide

• Jul 16, 2024

Sun-Loving Azaleas: Shade or Shine?

• Jul 12, 2024