what is the biology definition of photosynthesis

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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.

photosynthesis

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• 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

Photosynthesis is critical for the existence of the vast majority of life on Earth. It is the way in which virtually all energy in the biosphere becomes available to living things. As primary producers, photosynthetic organisms form the base of Earth’s food webs and are consumed directly or indirectly by all higher life-forms. Additionally, almost all the oxygen in the atmosphere is due to the process of photosynthesis. If photosynthesis ceased, there would soon be little food or other organic matter on Earth, most organisms would disappear, and Earth’s atmosphere would eventually become nearly devoid of gaseous oxygen.

The process of photosynthesis is commonly written as: 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2 . This means that the reactants, six carbon dioxide molecules and six water molecules, are converted by light energy captured by chlorophyll (implied by the arrow) into a sugar molecule and six oxygen molecules, the products. The sugar is used by the organism, and the oxygen is released as a by-product.

The ability to photosynthesize is found in both eukaryotic and prokaryotic organisms. The most well-known examples are plants, as all but a very few parasitic or mycoheterotrophic species contain chlorophyll and produce their own food. Algae are the other dominant group of eukaryotic photosynthetic organisms. All algae, which include massive kelps and microscopic diatoms , are important primary producers.  Cyanobacteria and certain sulfur bacteria are photosynthetic prokaryotes, in whom photosynthesis evolved. No animals are thought to be independently capable of photosynthesis, though the emerald green sea slug can temporarily incorporate algae chloroplasts in its body for food production.

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photosynthesis , the process by which green plants and certain other organisms transform light energy into chemical energy . During photosynthesis in green plants, light energy is captured and used to convert water , carbon dioxide , and minerals into oxygen and energy-rich organic compounds .

It would be impossible to overestimate the importance of photosynthesis in the maintenance of life on Earth . If photosynthesis ceased, there would soon be little food or other organic matter on Earth. Most organisms would disappear, and in time Earth’s atmosphere would become nearly devoid of gaseous oxygen. The only organisms able to exist under such conditions would be the chemosynthetic bacteria , which can utilize the chemical energy of certain inorganic compounds and thus are not dependent on the conversion of light energy.

Energy produced by photosynthesis carried out by plants millions of years ago is responsible for the fossil fuels (i.e., coal , oil , and gas ) that power industrial society . In past ages, green plants and small organisms that fed on plants increased faster than they were consumed, and their remains were deposited in Earth’s crust by sedimentation and other geological processes. There, protected from oxidation , these organic remains were slowly converted to fossil fuels. These fuels not only provide much of the energy used in factories, homes, and transportation but also serve as the raw material for plastics and other synthetic products. Unfortunately, modern civilization is using up in a few centuries the excess of photosynthetic production accumulated over millions of years. Consequently, the carbon dioxide that has been removed from the air to make carbohydrates in photosynthesis over millions of years is being returned at an incredibly rapid rate. The carbon dioxide concentration in Earth’s atmosphere is rising the fastest it ever has in Earth’s history, and this phenomenon is expected to have major implications on Earth’s climate .

Requirements for food, materials, and energy in a world where human population is rapidly growing have created a need to increase both the amount of photosynthesis and the efficiency of converting photosynthetic output into products useful to people. One response to those needs—the so-called Green Revolution , begun in the mid-20th century—achieved enormous improvements in agricultural yield through the use of chemical fertilizers , pest and plant- disease control, plant breeding , and mechanized tilling, harvesting, and crop processing. This effort limited severe famines to a few areas of the world despite rapid population growth , but it did not eliminate widespread malnutrition . Moreover, beginning in the early 1990s, the rate at which yields of major crops increased began to decline. This was especially true for rice in Asia. Rising costs associated with sustaining high rates of agricultural production, which required ever-increasing inputs of fertilizers and pesticides and constant development of new plant varieties, also became problematic for farmers in many countries.

A second agricultural revolution , based on plant genetic engineering , was forecast to lead to increases in plant productivity and thereby partially alleviate malnutrition. Since the 1970s, molecular biologists have possessed the means to alter a plant’s genetic material (deoxyribonucleic acid, or DNA ) with the aim of achieving improvements in disease and drought resistance, product yield and quality, frost hardiness, and other desirable properties. However, such traits are inherently complex, and the process of making changes to crop plants through genetic engineering has turned out to be more complicated than anticipated. In the future such genetic engineering may result in improvements in the process of photosynthesis, but by the first decades of the 21st century, it had yet to demonstrate that it could dramatically increase crop yields.

Another intriguing area in the study of photosynthesis has been the discovery that certain animals are able to convert light energy into chemical energy. The emerald green sea slug ( Elysia chlorotica ), for example, acquires genes and chloroplasts from Vaucheria litorea , an alga it consumes, giving it a limited ability to produce chlorophyll . When enough chloroplasts are assimilated , the slug may forgo the ingestion of food. The pea aphid ( Acyrthosiphon pisum ) can harness light to manufacture the energy-rich compound adenosine triphosphate (ATP); this ability has been linked to the aphid’s manufacture of carotenoid pigments.

General characteristics

The study of photosynthesis began in 1771 with observations made by the English clergyman and scientist Joseph Priestley . Priestley had burned a candle in a closed container until the air within the container could no longer support combustion . He then placed a sprig of mint plant in the container and discovered that after several days the mint had produced some substance (later recognized as oxygen) that enabled the confined air to again support combustion. In 1779 the Dutch physician Jan Ingenhousz expanded upon Priestley’s work, showing that the plant had to be exposed to light if the combustible substance (i.e., oxygen) was to be restored. He also demonstrated that this process required the presence of the green tissues of the plant.

In 1782 it was demonstrated that the combustion-supporting gas (oxygen) was formed at the expense of another gas, or “fixed air,” which had been identified the year before as carbon dioxide. Gas-exchange experiments in 1804 showed that the gain in weight of a plant grown in a carefully weighed pot resulted from the uptake of carbon, which came entirely from absorbed carbon dioxide, and water taken up by plant roots; the balance is oxygen, released back to the atmosphere. Almost half a century passed before the concept of chemical energy had developed sufficiently to permit the discovery (in 1845) that light energy from the sun is stored as chemical energy in products formed during photosynthesis.

This equation is merely a summary statement, for the process of photosynthesis actually involves numerous reactions catalyzed by enzymes (organic catalysts ). These reactions occur in two stages: the “light” stage, consisting of photochemical (i.e., light-capturing) reactions; and the “dark” stage, comprising chemical reactions controlled by enzymes . During the first stage, the energy of light is absorbed and used to drive a series of electron transfers, resulting in the synthesis of ATP and the electron-donor-reduced nicotine adenine dinucleotide phosphate (NADPH). During the dark stage, the ATP and NADPH formed in the light-capturing reactions are used to reduce carbon dioxide to organic carbon compounds. This assimilation of inorganic carbon into organic compounds is called carbon fixation.

Van Niel’s proposal was important because the popular (but incorrect) theory had been that oxygen was removed from carbon dioxide (rather than hydrogen from water, releasing oxygen) and that carbon then combined with water to form carbohydrate (rather than the hydrogen from water combining with CO 2 to form CH 2 O).

By 1940 chemists were using heavy isotopes to follow the reactions of photosynthesis. Water marked with an isotope of oxygen ( 18 O) was used in early experiments. Plants that photosynthesized in the presence of water containing H 2 18 O produced oxygen gas containing 18 O; those that photosynthesized in the presence of normal water produced normal oxygen gas. These results provided definitive support for van Niel’s theory that the oxygen gas produced during photosynthesis is derived from water.

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.

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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.

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Related Resources

What is photosynthesis?

Photosynthesis is the process plants, algae and some bacteria use to turn sunlight, carbon dioxide and water into sugar and oxygen.

• Photosynthetic processes
• Photosynthesis equation
• The carbon exchange
• How do plants absorb sunlight?

How does photosynthesis start?

• Location of photosynthesis

Light-dependent reactions

• The Calvin cycle

Types of photosynthesis

Additional resources.

Photosynthesis is the process used by plants, algae and some bacteria to turn sunlight into energy. The process chemically converts carbon dioxide (CO2) and water into food (sugars) and oxygen . The chemical reaction often relies on a pigment called chlorophyll, which gives plants their green color.  Photosynthesis is also the reason our planet is blanketed in an oxygen-rich atmosphere.

Types of photosynthetic processes

There are two types of photosynthesis: oxygenic and anoxygenic. They both follow very similar principles, but the former is the most common and is seen in plants, algae and cyanobacteria. 

During oxygenic photosynthesis, light energy transfers electrons from water (H2O) taken up by plant roots to CO2 to produce carbohydrates . In this transfer, the CO2 is "reduced," or receives electrons, and the water is "oxidized," or loses electrons. Oxygen is produced along with carbohydrates.

This process creates a balance on Earth, in which the carbon dioxide produced by breathing organisms as they consume oxygen in respiration is converted back into oxygen by plants, algae and bacteria.

Anoxygenic photosynthesis, meanwhile, uses electron donors that are not water and the process does not generate oxygen, according to "Anoxygenic Photosynthetic Bacteria" by LibreTexts . The process typically occurs in bacteria such as green sulfur bacteria and phototrophic purple bacteria. 

The Photosynthesis equation

Though both types of photosynthesis are complex, multistep affairs, the overall process can be neatly summarized as a chemical equation.

The oxygenic photosynthesis equation is: 

6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O

Here, six molecules of carbon dioxide (CO2) combine with 12 molecules of water (H2O) using light energy. The end result is the formation of a single carbohydrate molecule (C6H12O6, or glucose) along with six molecules each of oxygen and water.

Similarly, the various anoxygenic photosynthesis reactions can be represented as a single generalized formula:

CO2 + 2H2A + Light Energy → [CH2O] + 2A + H2O

The letter A in the equation is a variable, and H2A represents the potential electron donor. For example, "A" may represent sulfur in the electron donor hydrogen sulfide (H2S), according to medical and life sciences news site News Medical Life Sciences . 

How is carbon dioxide and oxygen exchanged?

Plants absorb CO2 from the surrounding air and release water and oxygen via microscopic pores on their leaves called stomata. 

When stomata open, they let in CO2; however, while open, the stomata release oxygen and let water vapor escape. Stomata close to prevent water loss, but that means the plant can no longer gain CO2 for photosynthesis. This tradeoff between CO2 gain and water loss is a particular problem for plants growing in hot, dry environments. 

How do plants absorb sunlight for photosynthesis?

Plants contain special pigments that absorb the light energy needed for photosynthesis.

Chlorophyll is the primary pigment used for photosynthesis and gives plants their green color, according to science education site Nature Education . Chlorophyll absorbs red and blue light and reflects green light. Chlorophyll is a large molecule and takes a lot of resources to make; as such, it breaks down towards the end of the leaf's life, and most of the pigment's nitrogen (one of the building blocks of chlorophyll) is resorbed back into the plant,  When leaves lose their chlorophyll in the fall, other leaf pigments such as carotenoids and anthocyanins begin to show. While carotenoids primarily absorb blue light and reflect yellow, anthocyanins absorb blue-green light and reflect red light, according to Harvard University's The Harvard Forest .

Related: What if humans had photosynthetic skin?

Pigment molecules are associated with proteins, which allow them the flexibility to move toward light and toward one another. A large collection of 100 to 5,000 pigment molecules constitutes an "antenna," according to an article by Wim Vermaas , a professor at Arizona State University. These structures effectively capture light energy from the sun, in the form of photons.

The situation is a little different for bacteria. While cyanobacteria contain chlorophyll, other bacteria, for example, purple bacteria and green sulfur bacteria, contain bacteriochlorophyll to absorb light for anoxygenic photosynthesis, according to " Microbiology for Dummies " (For Dummies, 2019). 

It was previously hypothesized that just a small number of photons would be needed to kickstart photosynthesis, but researchers never successfully observed this first step. However, in 2023, scientists discovered that photosynthesis appears to begin with a single photon. 

The researchers set up an experiment where a photon source spat out two photons at a time. One was absorbed by a detector, while the other hit a bacteria's chloroplast equivalent. When the second photon hit, photosynthesis began. 

After performing the test over 1.5 million times, the researchers confirmed that just one photon is needed to start photosynthesis.

Where in the plant does photosynthesis take place?

Photosynthesis occurs in chloroplasts, a type of plastid (an organelle with a membrane) that contains chlorophyll and is primarily found in plant leaves. 

Chloroplasts are similar to mitochondria , the energy powerhouses of cells, in that they have their own genome, or collection of genes, contained within circular DNA. These genes encode proteins that are essential to the organelle and to photosynthesis.

Inside chloroplasts are plate-shaped structures called thylakoids that are responsible for harvesting photons of light for photosynthesis, according to the biology terminology website Biology Online . The thylakoids are stacked on top of each other in columns known as grana. In between the grana is the stroma — a fluid containing enzymes, molecules and ions, where sugar formation takes place. 

Ultimately, light energy must be transferred to a pigment-protein complex that can convert it to chemical energy, in the form of electrons. In plants, light energy is transferred to chlorophyll pigments. The conversion to chemical energy is accomplished when a chlorophyll pigment expels an electron, which can then move on to an appropriate recipient. 

The pigments and proteins that convert light energy to chemical energy and begin the process of electron transfer are known as reaction centers.

When a photon of light hits the reaction center, a pigment molecule such as chlorophyll releases an electron.

The released electron escapes  through a series of protein complexes linked together, known as an electron transport chain. As it moves through the chain, it generates the energy to produce ATP (adenosine triphosphate, a source of chemical energy for cells) and NADPH — both of which are required in the next stage of photosynthesis in the Calvin cycle. The "electron hole" in the original chlorophyll pigment is filled by taking an electron from water. This splitting of water molecules releases oxygen into the atmosphere.

Light-independent reactions: The Calvin cycle

The Calvin cycle is the three-step process that generates sugars for the plant, and is named after Melvin Calvin , the Nobel Prize -winning scientist who discovered it decades ago. The Calvin cycle uses the ATP and NADPH produced in chlorophyll to generate carbohydrates. It takes plate in the plant stroma, the inner space in chloroplasts.

In the first step of this cycle, called carbon fixation, an enzyme called RuBP carboxylase/oxygenase, also known as rubiso, helps incorporate CO2 into an organic molecule called 3-phosphoglyceric acid (3-PGA). In the process, it breaks off a phosphate group on six ATP molecules to convert them to ADP, releasing energy in the process, according to LibreTexts.

In the second step, 3-PGA is reduced, meaning it takes electrons from six NADPH molecules and produces two glyceraldehyde 3-phosphate (G3P) molecules.

One of these G3P molecules leaves the Calvin cycle to do other things in the plant. The remaining G3P molecules go into the third step, which is regenerating rubisco. In between these steps, the plant produces glucose, or sugar.

Three CO2 molecules are needed to produce six G3P molecules, and it takes six turns around the Calvin cycle to make one molecule of carbohydrate, according to educational website Khan Academy.

There are three main types of photosynthetic pathways: C3, C4 and CAM. They all produce sugars from CO2 using the Calvin cycle, but each pathway is slightly different.

C3 photosynthesis

Most plants use C3 photosynthesis, according to the photosynthesis research project Realizing Increased Photosynthetic Efficiency (RIPE) . C3 plants include cereals (wheat and rice), cotton, potatoes and soybeans. This process is named for the three-carbon compound 3-PGA that it uses during the Calvin cycle. 

C4 photosynthesis

Plants such as maize and sugarcane use C4 photosynthesis. This process uses a four-carbon compound intermediate (called oxaloacetate) which is converted to malate , according to Biology Online. Malate is then transported into the bundle sheath where it breaks down and releases CO2, which is then fixed by rubisco and made into sugars in the Calvin cycle (just like C3 photosynthesis). C4 plants are better adapted to hot, dry environments and can continue to fix carbon even when their stomata are closed (as they have a clever storage solution), according to Biology Online. 

CAM photosynthesis

Crassulacean acid metabolism (CAM) is found in plants adapted to very hot and dry environments, such as cacti and pineapples, according to the Khan Academy. When stomata open to take in CO2, they risk losing water to the external environment. Because of this, plants in very arid and hot environments have adapted. One adaptation is CAM, whereby plants open stomata at night (when temperatures are lower and water loss is less of a risk). According to the Khan Academy, CO2 enters the plants via the stomata and is fixed into oxaloacetate and converted into malate or another organic acid (like in the C4 pathway). The CO2 is then available for light-dependent reactions in the daytime, and stomata close, reducing the risk of water loss. 

Discover more facts about photosynthesis with the educational science website sciencing.com . Explore how leaf structure affects photosynthesis with The University of Arizona . Learn about the different ways photosynthesis can be measured with the educational science website Science & Plants for Schools .  

This article was updated by Live Science managing editor Tia Ghose on Nov. 3, 2022.

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Daisy Dobrijevic joined  Space.com  in February 2022 as a reference writer having previously worked for our sister publication  All About Space  magazine as a staff writer. Before joining us, Daisy completed an editorial internship with the BBC Sky at Night Magazine and worked at the  National Space Centre  in Leicester, U.K., where she enjoyed communicating space science to the public. In 2021, Daisy completed a PhD in plant physiology and also holds a Master's in Environmental Science, she is currently based in Nottingham, U.K.

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photosynthesis

Definition of photosynthesis

Did you know.

Photosynthesis Has Greek Roots

The Greek roots of photosynthesis combine to produce the basic meaning "to put together with the help of light". Photosynthesis is what first produced oxygen in the atmosphere billions of years ago, and it's still what keeps it there. Sunlight splits the water molecules (made of hydrogen and oxygen) held in a plant's leaves and releases the oxygen in them into the air. The leftover hydrogen combines with carbon dioxide to produce carbohydrates, which the plant uses as food—as do any animals or humans who might eat the plant.

Examples of photosynthesis in a Sentence

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'photosynthesis.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

1898, in the meaning defined above

Dictionary Entries Near photosynthesis

photosynthate

photosynthetic ratio

Cite this Entry

“Photosynthesis.” Merriam-Webster.com Dictionary , Merriam-Webster, https://www.merriam-webster.com/dictionary/photosynthesis. Accessed 4 Sep. 2024.

Kids Definition

Kids definition of photosynthesis, medical definition, medical definition of photosynthesis, more from merriam-webster on photosynthesis.

Nglish: Translation of photosynthesis for Spanish Speakers

Britannica.com: Encyclopedia article about photosynthesis

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photosynthesis

Photosynthesis requires sunlight, chlorophyll, water, and carbon dioxide gas. Chlorophyll is a substance in all green plants, especially in the leaves. Plants take in water from the soil and carbon dioxide from the air.

Photosynthesis starts when chlorophyll absorbs energy from sunlight. Green plants use this light energy to change water and carbon dioxide into oxygen and nutrients called sugars. The plants use some of the sugars and store the rest. The oxygen is released into the air.

Photosynthesis is very important because almost all living things depend on plants for food. Photosynthesis is also important because of the oxygen it produces. Humans and other animals need to breathe in oxygen to survive.

Some living things other than plants also make their own food through photosynthesis. They include certain types of bacteria and algae.

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Photosynthesis: What Is It & How Does It Work?

16 November 2022

• 1 . What is Photosynthesis?
• 2 . What gas is produced by plants as a waste product of photosynthesis?
• 3 . Photosynthesis Equations
• 4 . Why is photosynthesis important?
• 5 . What product from photosynthesis is used to make cellulose?
• 6 . What type of reaction is photosynthesis? Is photosynthesis endothermic or exothermic?
• 7 . Factors affecting photosynthesis
• 8 . What name is given to a factor which is preventing any increase in photosynthesis?
• 9 . Where does photosynthesis take place? 
• 10 . Which part of a plant cell absorbs light for photosynthesis?
• 11 . How is a leaf adapted for photosynthesis? 
• 12 . What substance is tested for to see if photosynthesis has occurred in a leaf?
• 13 . Learn More About Photosynthesis

What is Photosynthesis?

Photosynthesis is a process where light energy is used to convert carbon dioxide and water into glucose and oxygen. This reaction is catalysed by enzymes in the chlorophyll of plant cells. 

What gas is produced by plants as a waste product of photosynthesis?

Oxygen is produced as a waste product. Some of it is used in the leaf for respiration, but some of it is not needed and diffuses out of the stomata of the leaf after the reaction is complete. 

Photosynthesis Equations

Photosynthesis word equation.

Carbon dioxide + water → glucose + oxygen

Chemical equation for photosynthesis

6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

Why is photosynthesis important?

Photosynthesis is important because it is the only reaction that exists in living things that takes carbon from the atmosphere (in the form of carbon dioxide) and converts it into a form that can be used by living organisms, glucose. Glucose is needed for an important reaction called respiration, which provides energy for all processes in metabolism. 

The carbon in glucose can also be converted into all the different types of biological molecules that are used in the plant for growth and metabolism, such as carbohydrates, lipids and proteins. These can then be passed on to all other types of organisms through feeding relationships. Plants are the producers at the start of every food chain and photosynthesis is essential to allow them to carry out this role. 

This diagram shows the uses of glucose within a plant, remembering that glucose is made as part of the photosynthesis reaction

What product from photosynthesis is used to make cellulose?

Glucose is also used to make cellulose, which is an important structural carbohydrate found in plant cell walls. Cellulose differs from starch not only in its structure, but also in the type of glucose it is made from. Starch is made from an isomer of glucose called alpha glucose, whereas cellulose is made from beta glucose. 

In cellulose the beta glucose units, called monomers, are positioned so that every other glucose is flipped 180° from the previous one in the chain. This allows the glucose monomers to form cross-linkages of hydrogen bonds between the chains, which increases the strength of the cellulose fibres; this is very important for its function of protecting and supporting the cell. 

This diagram shows the structure of cellulose where each beta glucose molecule is flipped 180o

More information: Cellulose (AQA A Level Biology)

What type of reaction is photosynthesis? Is photosynthesis endothermic or exothermic?

Photosynthesis is an endothermic reaction because it takes in energy from its surroundings in the form of light energy. There is a common misconception that endothermic reactions only take in heat energy and feel cold to the touch but any kind of energy can be used in an endothermic reaction. 

Factors affecting photosynthesis

The three main factors that affect the rate of photosynthesis are:

temperature,

light intensity, and

carbon dioxide concentration. 

How does temperature affect the rate of photosynthesis?

Temperature affects the rate of photosynthesis because the reaction is catalysed by enzymes. The rate of enzyme action increases with temperature because the reactants gain kinetic energy and so collide more frequently with the active site of the enzymes, forming more enzyme-substrate complexes. If the temperature rises too high it can cause the enzymes to become denatured and they are no longer able to function.

This graph shows the effect of temperature on rate of photosynthesis

How does light intensity affect the rate of photosynthesis?

Light intensity affects the rate of photosynthesis because light energy is a requirement for the reaction of photosynthesis. As the light intensity increases so does the rate of photosynthesis. However, this does not continue forever and eventually the rate of photosynthesis levels out because another factor limits the rate. 

This graph shows the effect of light intensity on the rate of photosynthesis

How does carbon dioxide concentration affect the rate of photosynthesis?

This graph shows the effect of carbon dioxide concentration on the rate of photosynthesis

What name is given to a factor which is preventing any increase in photosynthesis?

A factor which prevents an increase in photosynthesis is called a "limiting factor of photosynthesis".

Limiting factors of photosynthesis : A limiting factor of photosynthesis is a factor, such as carbon dioxide concentration or light intensity, that prevents the rate of photosynthesis from increasing because it is in short supply. 

Let’s use an analogy: let’s say you’re trying to bake as many cupcakes as possible for a cake stall at a local fundraising event. You go into your cupboard and search for the ingredients but you find you only have six eggs. In this scenario the maximum amount of cupcakes you can make depends on the amount of eggs you have. The number of eggs is the limiting factor. If you go out and buy more eggs you may then find that you only have enough sugar to make a certain amount of cupcakes, or perhaps a limited supply of flour. Each of these factors could act as a limiting factor in this scenario. 

Instead of cupcakes we can apply this to photosynthesis. If there isn’t enough carbon dioxide in the environment, the rate of photosynthesis can’t increase any further than the maximum rate dictated by the carbon dioxide. This is the limiting factor. 

Where does photosynthesis take place? 

Photosynthesis takes place in the leaves of plants. Within the leaves there is a specialised layer of cells called the palisade mesophyll layer, containing palisade cells. Although the palisade cells are specialised for photosynthesis, there are other cells in the leaf that can photosynthesise as well, such as the spongy mesophyll cells. It is important to have as many chloroplasts as possible in the leaf cells to reduce the amount of light that passes through the leaf without being absorbed by a chloroplast. 

This diagram shows the structure of a leaf and a typical plant cell

Which part of a plant cell absorbs light for photosynthesis?

These leaf cells are packed full of chloroplasts which contain the green pigment chlorophyll. The chlorophyll is where the enzymes that catalyse the reaction of photosynthesis are found. 

How is a leaf adapted for photosynthesis? 

Leaves are adapted for photosynthesis in many ways, such as:

Large surface area for absorbing light and carbon dioxide

Veins in the leaf support the cells to be held up to the light, they also contain vascular bundles with xylem vessels that carry water to the leaf for the reaction of photosynthesis

They are very thin to reduce the diffusion distance for carbon dioxide, which enters through the stomata on the base of the leaf, but must diffuse through to reach the palisade mesophyll at the top of the leaf

Large numbers of chlorophyll in the specialised cells of the leaf

The upper and lower epidermis of the leaf are thin and transparents to allow as much light as possible into the leaf

The spongy layer contains air spaces to allow the gasses carbon dioxide,oxygen and water vapour, to diffuse through the leaf space easily, whereas the palisade cells are packed tightly together at the top of the leaf to ensure very little light passes through the leaf without going through a palisade cell

The stomata are positioned on the bottom of the leaf (for most species of plant) to ensure the carbon dioxide can enter the leaf whilst also protecting against excess evaporation / water loss from the leaf

More information: Plant Tissues (AQA GCSE Biology)

What substance is tested for to see if photosynthesis has occurred in a leaf?

Starch is tested for to see if photosynthesis has occurred in a leaf. If the leaf contains starch it indicates that photosynthesis is happening and if it is not found then it indicates that photosynthesis is not happening. 

The reason for this is because glucose from photosynthesis is stored as starch after photosynthesis has taken place. Glucose must be stored as starch in the leaf cells because otherwise the glucose would lower the water potential of the cell and cause water to move into the cell by osmosis. Starch is insoluble and so does not affect the water potential of the cells. If the leaf is unable to photosynthesise (for example, if it is being kept in a dark space) the starch in the leaf is broken down and the glucose is released and used in the cell for respiration. 

The practical investigation steps shown in the image below describes how this test is carried out:

Learn More About Photosynthesis

Photosynthetic Reaction (AQA GCSE Biology)

Chloroplast Structures & their Functions (AQA A Level Biology)

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Written by Emma Archbold

Prior to working at SME, Emma was a Biology teacher for 5 years. During those years she taught three different GCSE exam boards and two A-Level exam boards, gaining a wide range of teaching expertise in the subject. Emma particularly enjoys learning about ecology and conservation. Emma is passionate about making her students achieve the highest possible grades in their exams by creating amazing revision resources!

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photosynthesis

[ foh-t uh - sin -th uh -sis ]

• the complex process by which carbon dioxide, water, and certain inorganic salts are converted into carbohydrates by green plants, algae, and certain bacteria, using energy from the sun and chlorophyll .

/ ˌfəʊtəʊsɪnˈθɛtɪk; ˌfəʊtəʊˈsɪnθɪsɪs /

• (in plants) the synthesis of organic compounds from carbon dioxide and water (with the release of oxygen) using light energy absorbed by chlorophyll
• the corresponding process in certain bacteria

/ fō′tō-sĭn ′ thĭ-sĭs /

• The process by which green plants, algae, diatoms, and certain forms of bacteria make carbohydrates from carbon dioxide and water in the presence of chlorophyll, using energy captured from sunlight by chlorophyll, and releasing excess oxygen as a byproduct. In plants and algae, photosynthesis takes place in organelles called chloroplasts . Photosynthesis is usually viewed as a two-step process. First, in the light reactions , the energy-providing molecule ATP is synthesized using light energy absorbed by chlorophyll and accessory pigments such as carotenoids and phycobilins, and water is broken apart into oxygen and a hydrogen ion, with the electron of the hydrogen transferred to another energy molecule, NADPH. The ATP and NADPH molecules power the second part of photosynthesis by the transfer of electrons. In these light-independent or dark reactions , carbon is broken away from carbon dioxide and combined with hydrogen via the Calvin cycle to create carbohydrates. Some of the carbohydrates, the sugars, can then be transported around the organism for immediate use; others, the starches, can be stored for later use.
• Compare chemosynthesis See Note at transpiration
• Use by green plants of the energy in sunlight to carry out chemical reactions , such as the conversion of carbon dioxide into oxygen . Photosynthesis also produces the sugars that feed the plant.

Derived Forms

• ˌphotosynˈthetically , adverb
• photosynthetic , adjective

Other Words From

• pho·to·syn·thet·ic [ foh-t, uh, -sin-, thet, -ik ] , adjective
• photo·syn·theti·cal·ly adverb
• non·photo·syn·thetic adjective

Word History and Origins

Origin of photosynthesis 1

A Closer Look

Compare meanings.

How does photosynthesis compare to similar and commonly confused words? Explore the most common comparisons:

• chemosynthesis vs. photosynthesis
• photosynthesis vs. cellular respiration
• photorespiration vs. photosynthesis

Example Sentences

Specifically, he was interested in the protein-based "reaction centers" in spinach leaves that are the basic mechanism for photosynthesis—the chemical process by which plants convert carbon dioxide into oxygen and carbohydrates.

Algae and plants use photosynthesis to turn sunlight into food.

According to the Washington Post, this happens because as the days shorten and turn frigid, it’s not worth it for some trees to expend energy to conduct photosynthesis.

In a steady state, most of the energy captured by photosynthesis is used up by the furnace of respiration and metabolism burning on Earth’s surface by its infrared layer of life.

There’s no sunlight beneath half a mile of ice, so of course there’s no photosynthesis.

Nevertheless, it was required, and at least it was more fun than studying algebra or photosynthesis.

Re-solarizing the food chain should be our goal in every way—taking advantage of the everyday miracle that is photosynthesis.

As the microbes moved toward the light to carry out photosynthesis, they projected the image of the stencil.

Timiriazeff, in his Croonian Lecture, was the first to see the connexion between photosynthesis and the Lagado research.

On the other hand, their ancestors, the green or yellow mastigota, form new plasm by photosynthesis like true cells.

There the miracle of life consists merely of the chemical process of plasmodomism by photosynthesis.

Like von Baeyer's hypothesis, this assumes that formaldehyde and oxygen are the first products of photosynthesis.

In general, starch is the final product of photosynthesis in most green plants; but there are many exceptions to this.

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Reviewed by: BD Editors

Plant Definition

Plants are multicellular organisms in the kingdom Plantae that use photosynthesis to make their own food. There are over 300,000 species of plants; common examples of plants include grasses, trees, and shrubs. Plants have an important role in the world’s ecosystems. They produce most of the world’s oxygen, and are important in the food chain, as many organisms eat plants or eat organisms which eat plants. The study of plants is called botany.

Plant Characteristics

Plants are autotrophs; they produce their own food. They do so via photosynthesis, which is the process of making nutrients such as sugars from light energy and carbon dioxide. Photosynthesis occurs in cell organelles called chloroplasts, which contain chlorophyll and carotenoids, molecules that absorb light energy and change it into a usable form. Heterotrophs, on the other hand, are organisms that cannot make their own food and must eat other organisms to survive. Many heterotrophs eat plants. Other heterotrophs eat animals that have eaten plants. Plants are primary producers in many ecosystems, giving them a vital role in the survival of many other organisms. In addition, oxygen is a byproduct of photosynthesis, and many organisms depend on oxygen to survive. We couldn’t live without plants.

Plants are multicellular organisms with eukaryotic cells. A eukaryotic cell is a relatively large cell with a true nucleus and other organelles that perform specific functions. Plants, protists, fungi, and animals all have eukaryotic cells. Plant cells are distinguished by their cell walls containing cellulose, chloroplasts that perform photosynthesis, and a large central vacuole that holds water and keeps the plant turgid. Prokaryotic cells, on the other hand, are small with no true nucleus or organelles except ribosomes, which produce proteins. Bacteria and archaea have prokaryotic cells.

Many plants have vascular tissue, such as xylem and phloem, that carries water and nutrients throughout the plant. This is particularly important for plants that grow upwards; water needs to travel from the roots up the stem to the leaves. Vascular tissue is found in more “complex” plants. Plants are believed to have evolved from algae-like ancestors. Today, most modern-day algae are classified as bacteria, not plants. However, green algae, which also have cellulose in their cell walls and have chloroplasts that perform photosynthesis, are sometimes grouped with plants.

Plants reproduce both sexually and asexually and have what is known as alternation of generations. A haploid stage alternates with a diploid stage. Haploid is when cells contain one set of chromosomes, while diploid is when cells contain two sets. (For reference, humans are diploid but their gametes—sperm and eggs—are haploid). In plants, two haploid gametes join to form a diploid zygote. This diploid zygote divides through mitosis to become a multicellular organism. It is called the sporophyte, and at maturity, it asexually produces haploid spores. The haploid spores then germinate into multicellular organisms called gametophytes. Gametophytes produce haploid gametes, which fuse to make a diploid organism, and the alternation between diploid and haploid starts all over again.

Types of Plants

Charophytes.

Charophytes are complex green algae such as stoneworts. They have cells with chloroplasts, cell walls containing cellulose, and store starch, as plants do. They reproduce sexually and some have sperm with flagella (tails that allow them to move), just like some plants do. Some fossil stoneworts are very similar to modern day ones.

Bryophytes are nonvascular land plants. They do not have vascular tissue, which is tissue that transports water and nutrients. They are found both on land and in water. Common examples of bryophytes are mosses, liverworts, and hornworts. Bryophytes are generally very similar to algae in their lack of a vascular system. They do have parts similar to roots, stems, and leaves, but these are not the true roots, stems, and leaves found in vascular plants. Liverworts were probably the first land plants to evolve. Hornworts have features of both algae and plants, and mosses, the most well-known bryophytes, are the members of this group that are most similar to vascular plants.

Seedless Vascular Plants

Seedless vascular plants produce embryos that are not protected by seeds. Instead, they reproduce via spores. Members of this group include ferns, horsetails, quillworts, clubmosses, and spikemosses. These plants used to be called pteridophytes, but this turned out to be an inaccurate group because ferns and horsetails are more closely related to seed plants than to quillworts, clubmosses, and spikemosses. Seedless vascular plants flourished during the Devonian period and in Carboniferous forests.

Gymnosperms

Gymnosperms include conifers and related plants like ginkgoes and cycads. Gymnosperms have “naked seeds”; their seeds are not contained within an ovary as in flowering plants. Instead, their seeds grow on the surface of leaves, or in the case of conifers, modified structures like cones. The most common example of a gymnosperm is probably the pine tree and its pinecones. Ginkgoes are also well known for being essentially unchanged from ancient ginkgo plants found in fossils from 270 million years ago.

Angiosperms

Angiosperms are flowering plants. They are the most widespread plants today, and over 295,000 different species are known. Their reproductive organs are flowers, which have male parts like stamen and pollen, and female parts like the pistil. When flowers are pollinated, fruits develop containing seeds. Angiosperms have more complex vascular tissue than gymnosperms do.

Related Biology Terms

• Eukaryotic cell – A relatively large cell with a true nucleus and organelles.
• Chloroplast – An organelle found in plant cells that contains chlorophyll; it is where photosynthesis takes place.
• Organelle – A specialized structure within a cell that carries out a certain function in that cell.
• Alternation of generations – The alternation of diploid and haploid stages in a plant’s life cycle.

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C4 plant n., plural: C4 plants Definition: A plant that utilizes the C 4 carbon fixation pathway

Table of Contents

Carbon fixation is a process of taking carbon dioxide in order to synthesize sugar, such as glucose. Thus, carbon dioxide is a vital step in photosynthesis , together with photolysis ( light reactions ) and Calvin Cycle (dark reactions). In general, plants are grouped based on the mechanism used for fixing carbon. These plant groups are C3 , C4, and CAM plants . C3 plants utilize the C3 pathway (the initial step of the Calvin-Benson Cycle ), C4 plants employ the C4 pathway, and CAM plants use the Crassulacean acid metabolism pathway. Let us know more about them, especially the C4 plants!

C4 Plants Definition

A C4 plant fixes CO 2 into a molecule containing four carbon atoms before initiating the Calvin-Benson cycle of photosynthesis . The C4 pathway is also known as the Hatch–Slack pathway . It is one of three photosynthetic pathways of carbon fixation in plants that have been discovered. The C4 cycle was discovered by Marshall Davidson Hatch and Charles Roger Slack in the 1960s, thus, the name. According to this, some plants, when provided with 14CO 2 , aggregate the 14C label into four-carbon molecules first.

What is a C4 plant? In the mesophyll cell, CO 2 is coupled to the primary carbon dioxide acceptor in C4 plants phosphoenolpyruvate , resulting in the creation of a four-carbon molecule ( oxaloacetate ), which is then shuttled to the bundle sheath cell , where it is decarboxylated to free carbon dioxide for carbon assimilation in the C3 pathway .

Other types: C3 plants and CAM plant

The Calvin cycle begins with the fixation of carbon dioxide by RuBisCO, and plants that rely only on this “conventional” approach are referred to as C3 plants , after the three-carbon molecule ( 3-PGA ) generated as a consequence of the process. Rice, wheat, soybeans, and all trees are classed as C3 plants, accounting for nearly 85 % of all plant species in the world.

Cacti and pineapples, for example, employ the crassulacean acid metabolism (CAM) photosynthesis pathway to save water and reduce photorespiration while growing in dry areas. The name comes from the Crassulaceae family of plants, which is the first group of plants when scientists discovered the pathway. (Academy, 2022)

Watch this vid to learn the different anatomical and physiological properties of C3, C4, and CAM plants

• Going through the C4 carbon fixation pathway . This pathway is when the CO 2 is first bound to phosphoenolpyruvate in the mesophyll cell. Then, the process proceeds to the Calvin Cycle. (Thus, C4 plants go through the C3 pathway as well but C3 plants do not go through the C4 pathway but directly proceed to the C3 pathway)
• The C4 carbon fixation pathway results in the formation of a four-carbon compound (oxaloacetate).  The oxaloacetate is shuttled to the bundle sheath cell where it will be decarboxylated to liberate the CO 2 to be utilized in the C 3 pathway.
• Most C 4 plants have special leaf anatomy (called Kranz anatomy ) in which the vascular bundles are surrounded by bundle sheath cells. The Kranz anatomy facilitates the metabolite exchange between the two different cell types, specifically the mesophyll cells and the bundle sheath cells.
• Upon fixation of CO 2 into a 4-carbon compound in the mesophyll cells, this compound is transported to the bundle sheath cells where it will be decarboxylated. The CO 2 is re-fixed via the C 3 pathway.
• The enzyme involved in C4 carbon fixation is PEP carboxylase (for the reaction: PEP + CO 2 → oxaloacetate + Pi).
• The enzyme that catalyzes the first step of the CO 2 concentrating mechanism in C4 plants is the carbonic anhydrase (for the reaction: CO 2 → HCO 3 in the cytosol of mesophyll cell).
• In this mechanism, the tendency of RuBisCO (the first enzyme in the Calvin cycle ) to photorespire, or waste energy by having a high affinity to oxygen and thus, using oxygen to break down carbon compounds to CO 2 , is minimized.
• The additional step (C4 pathway) requires energy (ATP) that is used to regenerate PEP (when pyruvate is returned to the mesophyll cell for the C3 pathway). Thus, for every CO 2 shuttled to RuBisCO, there is a net cost of 1 ATP. Despite that, C4 plants through the C4 pathway are better adapted than C 3 plants in an environment with high daytime temperatures, intense sunlight, drought, or nitrogen or CO 2 limitation.
• Examples of C 4 plants include sugarcane, maize, sorghum, amaranth, etc.

Types of Photosynthesis

Anoxygenic photosynthesis and oxygenic photosynthesis are the two forms of photosynthesis in plants that occur in the environment. Although they both operate on very similar principles, oxygenic photosynthesis is the more prevalent type and may be found in plants, algae, and cyanobacteria . Anoxygenic photosynthesis , on the other hand, makes use of electron donors that are not water and does not result in the production of oxygen . Bacteria such as green sulfur bacteria and phototrophic purple bacteria are examples of organisms that undergo this procedure. (Dobrijevic, 2021)

Oxygenic photosynthesis and photorespiration

Oxygenic photosynthesis, the type of photosynthesis that prevails in plants, coevolved with photorespiration. Photorespiration may seem a wasteful process as it lowers photosynthesis efficiency by using O 2 and releasing CO 2 , which is one of the essential requirements in photosynthesis. However, photorespiration helps maintain the redox balance in plant cells. It is also a way for plants to convert phosphoglycolate, which is a toxic compound, into non-toxic metabolites. Furthermore, it serves as an energy sink (for ATP and NADH).

C4 Pathway and Photorespiration

In plants, there are two types of respiration: dark plant respiration and photorespiration . Photorespiration is a process that occurs in plants when they are exposed to light conditions and results in the loss of fixed carbon as carbon dioxide. It is sometimes referred to as the C2 cycle . Photorespiration makes use of three organelles, particularly, chloroplasts , peroxisomes , and mitochondria .

The oxidative photosynthetic carbon cycle is often referred to as photorespiration (or C2 cycle). It is one of the key metabolic steps in plants. The enzyme RuBisCO oxygenates RuBP ( R ibulose 1,5- b is p hosphate), absorbing part of the energy produced during photosynthesis. RuBisCO should react with RuBP to produce carbon dioxide (carboxylation), which is an essential step in the Calvin–Benson cycle.

Low activity of RuBisCO limits the rate of photosynthesis. (ScienceDaily, 2020) Roughly 25% of RuBisCO reaction (by the addition of oxygen to RuBP; oxygenation reaction) results in a product that cannot be utilized in the Calvin–Benson cycle. As a result of this process, photosynthesis efficiency is lowered. This is not a small decrease in efficiency as it could potentially reach up to 25% in C3 plants .

C4 Photosynthesis Evolution

Most terrestrial plants use the C3 pathway for carbon fixation. RuBisCO directly fixes CO 2 into C3 compounds in mesophyll cells. In C4 plants, carbon fixation includes additional step by first incorporating CO 2 into C4 compounds in the mesophyll cells, and then transported into the bundle sheath cells for decarboxylation, releasing CO 2 , and then using the C3 compounds into the Calvin Benson cycle.

The C3-C4 intermediate species are regarded as the species in this evolutionary transitionary phase, i.e., between C3 and C4 photosynthetic pathways.

The independent emergence of C4 plants within many Angiosperm clades is considered an example of convergent evolution . They are unrelated species but were able to evolve a similar trait, which, in this case, is the strategy for carbon fixation via the C4 pathway.

In the family Chenopodiaceae, this C4 plant family has the greatest number of C4 species and is the most diverse in C4 eudicot lineages. Although they share the same CO 2 -concentrating strategy, they have diverse Kranz anatomy, which led to the following distinct forms: salsoloid, suaedoid, kochioid, and atriplicoid . (Edwards, 2000)

How the C4 pathway evolved remains unclear although the colonization of C4 plants was apparently favored by environmental selection factors, such as atmospheric CO 2 depletion, intense light in open habitats, and high temperature.

The drop in atmospheric carbon dioxide and the emergence of seasonal climatic conditions (i.e., from warm and moist to slightly cooler conditions) at the Eocene/Oligocene boundary (∼45 to 25 million years ago) could be the necessary selection agent to favor C4 photosynthesis and drive the thriving of C4 plants, especially in drought-prone and saline habitats. (Kadereit, et al., 2012)

C4 Plant Process

In C4 plants, light-dependent activities and the Calvin cycle occur in distinct cells. Calvin cycle reactions occur in particular cells found around the leaf veins. In the spongy tissue of mesophyll cells, light-dependent reactions take place. In c4 plants, the Calvin cycle operates in bundle-sheath cells. Take into consideration the C4 cycle steps to see how this division is advantageous.

At the start, in the mesophyll cells, carbon dioxide is fixed, which leads to the formation of simple 4-carbon organic acids (oxaloacetate). These reactions are catalyzed by PEP carboxylase , which is a non-RuBisCO enzyme with no attraction for the amino acid O.

After this, oxaloacetate is converted to malate , a structurally similar chemical capable of passing through the membrane of bundle-sheath cells. When malate decomposes, a molecule of CO 2 is liberated from the bundle sheath. RuBisCO, like C3 photosynthesis, fixes carbon dioxide and transforms it into sugars through the Calvin cycle. The following is a C4 cycle diagram:

From the bundle sheath cells, ATP must be converted into the three-carbon “ ferry ” molecule and prepared for the next stage, which is to carry out another molecule of ambient carbon dioxide from the cell membrane. As a result of the ongoing pumping of carbon dioxide into adjacent bundle-sheath cells in the form of malate (malic acid), by the mesophyll cells, the level of carbon dioxide concentration remains high relative to oxygen, right around RuBisCO. Photorespiration is decreased as a consequence of this strategy.

About 3% of vascular plants use the C4 route; notable examples include sugarcane, crabgrass, and maize. While C4 plants can be found in abundance in hotter conditions, their numbers are dramatically reduced in cooler environments.

According to studies, if the temperature is high enough, the advantages of decreased photorespiration will very certainly balance the ATP cost of carbon dioxide transport from the mesophyll cell into the bundle-sheath cell. (Academy, 2022) Nevertheless, since C4 morphological and biochemical adaptations demand more energy and resources from the plant than C3 photosynthesis, wild-type C3 plants are usually more photosynthetically effective and efficient under colder conditions. (Modules, 2018)

However, since C4 plants tend to have higher photosynthetic performance because of having a C4 pathway in addition to the C3 pathway, especially in areas with high temperatures, modern research and technology in plant sciences have been employed to improve C3 plants’ photosynthetic performance. One of these strategies is to transfer the C4 traits to C3 plants. Through molecular or genetic engineering, important crops, such as rice and wheat, which are C3 plants could benefit from this. By recombinant DNA technology, the photosynthetic enzymes involved in the C4 pathway can be induced to express at high levels and in desired locations, for example by inducing cell-specific expression of photosynthetic genes in the bundle sheath of rice leaves. (Miyao, 2002) Predictive models implicate that rice yield could improve by generating C4 rice. (Hibberd et al., 2008)

C4 Plants Examples

Is maize a c4 plant?  Yes, it is a C4 plant. In fact, many crops are, such as sugar cane, maize, millet, sorghum, and switchgrass. They are commonly found in warm to high-temperature environments. Southwest Asia and Central Asia have been cited as the origin of at least 20 of the 38 lineages of C4 Eudicots apart from the C4 Monocots . (Rudov et al., 2020)

Try to answer the quiz below to check what you have learned so far about C4 plants.

Choose the best answer. 

Send Your Results (Optional)

• Academy, K. (2022). C3, C4, and CAM plants. Retrieved 26 March, 2022, from https://www.khanacademy.org/science/biology/photosynthesis-in-plants#photorespiration–c3-c4-cam-plants
• Dobrijevic, D. (2021). What is photosynthesis. Retrieved 26 March, 2022, from https://www.livescience.com/51720-photosynthesis.html
• Edwards, G. E., Kiirats, O., Laisk, A., & Okita, T. W. (2000). Requirements for the CO2-concentrating mechanism in C4 plants relative to limitations on carbon assimilation in rice**Citation: Sheehy JE, Mitchell PL, Hardy B, editors. 2000. Redesigning rice photosynthesis to increase yield. Proceedings of the Workshop on The Quest to Reduce Hunger: Redesigning Rice Photosynthesis, 30Nov.-3 Dec. 1999. Los Baños. Philippines. Makati City (Philippines): International Rice Research Institute and Amsterdam (The Netherlands): Elsevier Science B.V. 293 p. Redesigning Rice Photosynthesis to Increase Yield, Proceedings of the Workshop on the Quest to Reduce Hunger: Redesigning Rice Photosynthesis , 99–112. https://doi.org/10.1016/s0928-3420(00)80009-9
• Hibberd, J. M., Sheehy, J. E., & Langdale, J. A. (2008). Using C4 photosynthesis to increase the yield of rice—rationale and feasibility. Current Opinion in Plant Biology , 11(2), 228–231. https://doi.org/10.1016/j.pbi.2007.11.002
• Kadereit, G., Ackerly, D., and Pirie, M.D. (2012). A broader model for C4 photosynthesis evolution in plants inferred from the goosefoot family (Chenopodiaceae s.s.). Proceedings of the Royal Society B: Biological Sciences. https://royalsocietypublishing.org/doi/10.1098/rspb.2012.0440
• Modules, I. (2018). C3 and C4 photosynthesis. Retrieved 26 March, 2022, from https://serc.carleton.edu/integrate/teaching_materials/food_supply/student_materials/1167#:~:text=Examples%20of%20C4%20plants%20include,more%20photosynthetically%20efficient%20and%20productive.
• Nakamura, N., Iwano, M., Havaux, M., Yokota, A., & Munekage, Y. N. (2013). Promotion of cyclic electron transport around photosystem I during the evolution of NADP-malic enzyme-type C 4 photosynthesis in the genus Flaveria .  New Phytologist ,  199 (3), 832–842. https://doi.org/10.1111/nph.12296
• Nomura, M., Katayama, K., Nishimura, A., Ishida, Y., Ohta, S., Komari, T., Miyao-Tokutomi, M., Tajima, S., & Matsuoka, M. (2000).  Plant Molecular Biology ,  44 (1), 99–106. https://doi.org/10.1023/a:1006461812053
• Rudov, A., Mashkour, M., Djamali, M., & Akhani, H. (2020). A Review of C4 Plants in Southwest Asia: An Ecological, Geographical and Taxonomical Analysis of a Region With High Diversity of C4 Eudicots. Frontiers in Plant Science , 11. https://doi.org/10.3389/fpls.2020.546518
• ScienceDaily. (2020). Successful improvement of the catalytic activity of photosynthetic CO2 fixing enzyme Rubisco. ScienceDaily . https://www.sciencedaily.com/releases/2020/09/200915090123.htm
• ‌Topper. (2022). Difference between C3 and C4 Plant. Retrieved 26 March, 2022, from https://www.toppr.com/guides/biology/difference-between/c3-and-c4-plants/#:~:text=C3%20plants%20use%20the%20C3,the%20dark%20reaction%20of%20photosynthesis.&text=These%20plants%20are%20cool%2Dseason,commonly%20found%20in%20dry%20areas.

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Last updated on June 11th, 2022

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