what is the final product and main goal of photosynthesis

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What Is the End Product of Photosynthesis?

Describe What a Photosystem Does for Photosynthesis

Humans and most other animals need certain things to survive. Oxygen is one of them, and the carbohydrate glucose is another. Fortunately for them, plants (and certain bacteria and algae) produce both of these as the result of a complex process known as photosynthesis.

The Formula

The formula associated with the process of photosynthesis is

6H 2 O + 6CO 2 = C 6 H 12 O 6 + 6O 2 .

This formula tells you is that six molecules of water plus six molecules of carbon dioxide will produce one molecule of glucose plus six molecules of oxygen. This entire process goes through two distinct stages before it is completed. The first stage is a light-dependent process and the second stage is a light-independent process.

Light Dependent

In the light-dependent process, the electrons of the chloroplasts (special organelles used to carry out photosynthesis) are excited into a higher energy state when they are bombarded with light. These excited electrons cause a series of reactions that produce adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). ATP and NADPH are then used to make carbon bonds in the light-independent process. Water molecules present in the light-dependent process are split. Their oxygen molecules are released into the atmosphere.

Light Independent

Recall the splitting of the water molecules in the light-dependent process that released oxygen molecules into the atmosphere. Since water is H 2 0, there is still a hydrogen atom remaining. This hydrogen atom is used in the light-independent process when plants take carbon dioxide from the atmosphere. The carbon dioxide and hydrogen become bound together through a process called carbon fixation, which forms a non-specific carbohydrate.

Photophosphorylation

Photophosphorylation is the process by which light energy produces NADPH. Special pigments found in the plant’s cells known as chlorophyll make this process possible. The two main types of chlorophyll are chlorophyll A and chlorophyll B. In simple terms, the electrons of water molecules present in chlorophyll B become excited by the presence of light. Chlorophyll B takes one of these excited electrons splitting the H 2 O molecule into H + and O -2 . O -2 is converted into O 2 and released into the atmosphere. The excited electron is attached to a primary electron receptor, and through a series of complex reactions forms NADPH. NADPH is the energy carrier used in carbon fixation.

The Calvin Cycle

Plants produce glucose in a process known as the Calvin cycle. The carbon dioxide captured in the light-independent process is processed in this cycle. For every six molecules of carbon dioxide captured and put into the cycle, one molecule of glucose is produced. The chemical that captures the carbon dioxide for use in the Calvin cycle is ribulose biphosphate.

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5.1: Overview of Photosynthesis

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All living organisms on earth consist of one or more cells. Each cell runs on the chemical energy found mainly in carbohydrate molecules (food), and the majority of these molecules are produced by one process: photosynthesis. Through photosynthesis, certain organisms convert solar energy (sunlight) into chemical energy, which is then used to build carbohydrate molecules. The energy used to hold these molecules together is released when an organism breaks down food. Cells then use this energy to perform work, such as cellular respiration .

The energy that is harnessed from photosynthesis enters the ecosystems of our planet continuously and is transferred from one organism to another. Therefore, directly or indirectly, the process of photosynthesis provides most of the energy required by living things on earth. Photosynthesis also results in the release of oxygen into the atmosphere. In short, to eat and breathe, humans depend almost entirely on the organisms that carry out photosynthesis.

CONCEPT IN ACTION

Click the following link to learn more about photosynthesis.

Solar Dependence and Food Production

Some organisms can carry out photosynthesis, whereas others cannot. An autotroph is an organism that can produce its own food. The Greek roots of the word autotroph mean “self” ( auto ) “feeder” ( troph ). Plants are the best-known autotrophs, but others exist, including certain types of bacteria and algae (Figure \(\PageIndex{1}\)). Oceanic algae contribute enormous quantities of food and oxygen to global food chains. Plants are also photoautotrophs, a type of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemical energy in the form of carbohydrates. All organisms carrying out photosynthesis require sunlight.

Heterotrophs are organisms incapable of photosynthesis that must therefore obtain energy and carbon from food by consuming other organisms. The Greek roots of the word heterotroph mean “other” ( hetero ) “feeder” ( troph ), meaning that their food comes from other organisms. Even if the food organism is another animal, this food traces its origins back to autotrophs and the process of photosynthesis. Humans are heterotrophs, as are all animals. Heterotrophs depend on autotrophs, either directly or indirectly. Deer and wolves are heterotrophs. A deer obtains energy by eating plants. A wolf eating a deer obtains energy that originally came from the plants eaten by that deer. The energy in the plant came from photosynthesis, and therefore it is the only autotroph in this example (Figure \(\PageIndex{2}\)). Using this reasoning, all food eaten by humans also links back to autotrophs that carry out photosynthesis.

BIOLOGY IN ACTION: 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 contains hundreds, if not thousands, of different products for customers to buy and consume (Figure \(\PageIndex{3}\)).

Although there is a large variety, each item links back to photosynthesis. Meats and dairy products link to photosynthesis because the animals were fed plant-based foods. The breads, cereals, and pastas come largely from grains, which are the seeds of photosynthetic plants. What about desserts and drinks? All of these products contain sugar—the basic carbohydrate molecule produced directly from photosynthesis. The photosynthesis connection applies to every meal and every food a person consumes.

Main Structures and Summary of Photosynthesis

Photosynthesis requires sunlight, carbon dioxide, and water as starting reactants (Figure \(\PageIndex{4}\)). After the process is complete, photosynthesis releases oxygen and produces carbohydrate molecules, most commonly glucose. These sugar molecules contain the energy that living things need to survive.

The complex reactions of photosynthesis can be summarized by the chemical equation shown in Figure \(\PageIndex{5}\).

Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex, as in the way that the reaction summarizing cellular respiration represented many individual reactions. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the physical structures involved.

In plants, photosynthesis takes place primarily in leaves, which consist of many layers of cells and have differentiated top and bottom sides. The process of photosynthesis occurs not on the surface layers of the leaf, but rather in a middle layer called the mesophyll (Figure \(\PageIndex{6}\)). The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata.

In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast. In plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double (inner and outer) membrane. Within the chloroplast is a third membrane that forms stacked, disc-shaped structures called thylakoids. Embedded in the thylakoid membrane are molecules of chlorophyll, a pigment (a molecule that absorbs light) through which the entire process of photosynthesis begins. Chlorophyll is responsible for the green color of plants. The thylakoid membrane encloses an internal space called the thylakoid space. Other types of pigments are also involved in photosynthesis, but chlorophyll is by far the most important. As shown in Figure \(\PageIndex{6}\), a stack of thylakoids is called a granum, and the space surrounding the granum is called stroma (not to be confused with stomata, the openings on the leaves).

ART CONNECTION

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

The Two Parts of Photosynthesis

Photosynthesis takes place in two stages: the light-dependent reactions and the Calvin cycle. In the light-dependent reactions, which take place at the thylakoid membrane, chlorophyll absorbs energy from sunlight and then converts it into chemical energy with the use of water. The light-dependent reactions release oxygen from the hydrolysis of water as a byproduct. In the Calvin cycle, which takes place in the stroma, the chemical energy derived from the light-dependent reactions drives both the capture of carbon in carbon dioxide molecules and the subsequent assembly of sugar molecules. The two reactions use carrier molecules to transport the energy from one to the other. The carriers that move energy from the light-dependent reactions to the Calvin cycle reactions can be thought of as “full” because they bring energy. After the energy is released, the “empty” energy carriers return to the light-dependent reactions to obtain more energy.

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

Only certain organisms, called autotrophs, can perform photosynthesis; they require the presence of chlorophyll, a specialized pigment that can absorb light and convert light energy into chemical energy. Photosynthesis uses carbon dioxide and water to assemble carbohydrate molecules (usually glucose) and releases oxygen into the air. Eukaryotic autotrophs, such as plants and algae, have organelles called chloroplasts in which photosynthesis takes place.

Art Connections

Figure \(\PageIndex{6}\): On a hot, dry day, plants close their stomata to conserve water. What impact will this have on photosynthesis?

Levels of carbon dioxide (a reactant) will fall, and levels of oxygen (a product) will rise. As a result, the rate of photosynthesis will slow down.

Contributors and Attributions

Samantha Fowler (Clayton State University), Rebecca Roush (Sandhills Community College), James Wise (Hampton University). Original content by OpenStax (CC BY 4.0; Access for free at https://cnx.org/contents/b3c1e1d2-83...4-e119a8aafbdd ).

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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What Are the Products of Photosynthesis?

Photosynthesis is a set of chemical reactions that plants and other organisms use to make chemical energy in the form of sugar. Like any chemical reaction, photosynthesis has reactants and products . Overall, the reactants of photosynthesis are carbon dioxide and water, while the products of photosynthesis are oxygen and glucose (a sugar).

Here’s a closer look at the products of photosynthesis and the balanced equation for the reaction.

The reactants for photosynthesis are carbon dioxide and water, while the products are the sugar glucose and oxygen.

Balanced Chemical Equation for Photosynthesis

Photosynthesis actually involves many chemical reactions, but the net balanced equation is that six moles of carbon dioxide react with six moles of water to produce one mole of glucose and six moles of oxygen. Light from the Sun provides the activation energy for the reaction. Sometimes light is listed in the balanced equation as a reactant, but it’s usually omitted.

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

Carbon Dioxide + Water + Light → Glucose + Oxygen

Closer Look at the Products of Photosynthesis

Photosynthesis occurs in a series of steps that are classified as light-dependent reactions and light-independent reactions. Adding up the reactants and products of these reactions gives the overall equation for photosynthesis, but it’s good to know the inputs and outputs for each stage.

Light-Dependent Reactions

The light-dependent reactions or light reactions absorb certain wavelengths of light to make adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH). The light reactions occur in the chloroplast thylakoid membrane. The overall balanced equation 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

Light-Independent Reactions

While the light reactions use water, the light-independent reactions use carbon dioxide. The light-independent reactions are also called the dark reactions. These reactions do not require darkness, but they don’t depend on light to proceed. In plants, algae, and cyanobacteria, the dark reactions are called the Calvin cycle. Bacteria use different reactions, including the reverse Krebs cycle.

The overall balanced equation for the light-independent reactions (Calvin cycle) in plants 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

Finally, the three-carbon product from the Calvin cycle becomes glucose during the process of carbon fixation.

Other Products of Photosynthesis

Glucose is the direct product of photosynthesis, but plants turn most of the sugar into other compounds. These are indirect products. Linking glucose units forms starch and cellulose. Cellulose is a structural material. Plants store starch or link it to fructose (another sugar) to form sucrose (table sugar).

What Is Not a Product of Photosynthesis?

On an exam, you may need to identify which chemical is not a product of photosynthesis. For the overall process, choose any answer except “glucose” or “oxygen.” It’s good to know the overall reactants and products of the light reactions and dark reactions, in case you’re asked about them. The products of the light reactions are ATP , NADPH, protons, and oxygen. The products of the dark reactions are C 3 H 6 O 3 -phosphate, ADP, inorganic phosphate, NADP + , and water.

Where Does Photosynthesis Occur?

In addition to knowing the reactants and products of photosynthesis, you may need to know where photosynthesis occurs in different organisms.

• In plants, photosynthesis occurs in organelles called chloroplasts. Photosynthetic protists also contain chloroplasts. Leaves contain the highest concentration of chloroplasts in plants. Plants obtain carbon dioxide via diffusion through leaf stomata. Water comes from the roots and travels to the leaves via the xylem . Chlorophyll in chloroplasts absorbs solar energy. Oxygen from photosynthesis exits the plant via leaf stomata.
• Photosynthesis occurs in photosynthetic bacteria in the plasma membrane. Chlorophyll or related pigments are embedded in this membrane.
• 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.

Related Posts

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.

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

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?

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What Are the Products of Photosynthesis?

Result of Photosynthesis in Plants

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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 carbon dioxide and water to produce sugar ( glucose ) and oxygen . 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 these reactions 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 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 photosynthesis on a test, you may be asked to identify the products of the reaction. 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.
• Photosynthesis Basics - Study Guide
• Photosynthesis Vocabulary Terms and Definitions
• The Photosynthesis Formula: Turning Sunlight into Energy
• Calvin Cycle Steps and Diagram
• 10 Fascinating Photosynthesis Facts
• Chloroplast Function in Photosynthesis
• Chlorophyll Definition and Role in Photosynthesis
• What Is the Primary Function of the Calvin Cycle?
• The Balanced Chemical Equation for Photosynthesis
• All About Photosynthetic Organisms
• Examples of Chemical Reactions in Everyday Life
• Thylakoid Definition and Function
• Simple Chemical Reactions
• Chemosynthesis Definition and Examples
• An Introduction to Types of Respiration
• Learn About Diffusion

5.1 Overview of Photosynthesis

Learning objectives.

• Summarize the process of photosynthesis
• Explain the relevance of photosynthesis to other living things
• Identify the reactants and products of photosynthesis
• Describe the main structures involved in photosynthesis

All living organisms on earth consist of one or more cells. Each cell runs on the chemical energy found mainly in carbohydrate molecules (food), and the majority of these molecules are produced by one process: photosynthesis. Through photosynthesis, certain organisms convert solar energy (sunlight) into chemical energy, which is then used to build carbohydrate molecules. The energy used to hold these molecules together is released when an organism breaks down food. Cells then use this energy to perform work, such as cellular respiration.

The energy that is harnessed from photosynthesis enters the ecosystems of our planet continuously and is transferred from one organism to another. Therefore, directly or indirectly, the process of photosynthesis provides most of the energy required by living things on earth.

Photosynthesis also results in the release of oxygen into the atmosphere. In short, to eat and breathe, humans depend almost entirely on the organisms that carry out photosynthesis.

Link to Learning

Click the following link to learn more about photosynthesis.

Solar Dependence and Food Production

Some organisms can carry out photosynthesis, whereas others cannot. An autotroph is an organism that can produce its own food. The Greek roots of the word autotroph mean “self” ( auto ) “feeder” ( troph ). Plants are the best-known autotrophs, but others exist, including certain types of bacteria and algae ( Figure 5.2 ). Oceanic algae contribute enormous quantities of food and oxygen to global food chains. Plants are also photoautotrophs , a type of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemical energy in the form of carbohydrates. All organisms carrying out photosynthesis require sunlight.

Heterotrophs are organisms incapable of photosynthesis that must therefore obtain energy and carbon from food by consuming other organisms. The Greek roots of the word heterotroph mean “other” ( hetero ) “feeder” ( troph ), meaning that their food comes from other organisms. Even if the food organism is another animal, this food traces its origins back to autotrophs and the process of photosynthesis. Humans are heterotrophs, as are all animals. Heterotrophs depend on autotrophs, either directly or indirectly. Deer and wolves are heterotrophs. A deer obtains energy by eating plants. A wolf eating a deer obtains energy that originally came from the plants eaten by that deer. The energy in the plant came from photosynthesis, and therefore it is the only autotroph in this example ( Figure 5.3 ). Using this reasoning, all food eaten by humans also links back to autotrophs that carry out 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 contains hundreds, if not thousands, of different products for customers to buy and consume ( Figure 5.4 ).

Although there is a large variety, each item links back to photosynthesis. Meats and dairy products link to photosynthesis because the animals were fed plant-based foods. The breads, cereals, and pastas come largely from grains, which are the seeds of photosynthetic plants. What about desserts and drinks? All of these products contain sugar—the basic carbohydrate molecule produced directly from photosynthesis. The photosynthesis connection applies to every meal and every food a person consumes.

Main Structures and Summary of Photosynthesis

Photosynthesis requires sunlight, carbon dioxide, and water as starting reactants ( Figure 5.5 ). After the process is complete, photosynthesis releases oxygen and produces carbohydrate molecules, most commonly glucose. These sugar molecules contain the energy that living things need to survive.

The complex reactions of photosynthesis can be summarized by the chemical equation shown in Figure 5.6 .

Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex, as in the way that the reaction summarizing cellular respiration represented many individual reactions. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the physical structures involved.

In plants, photosynthesis takes place primarily in leaves, which consist of many layers of cells and have differentiated top and bottom sides. The process of photosynthesis occurs not on the surface layers of the leaf, but rather in a middle layer called the mesophyll ( Figure 5.7 ). The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata .

In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast . In plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double (inner and outer) membrane. Within the chloroplast is a third membrane that forms stacked, disc-shaped structures called thylakoids . Embedded in the thylakoid membrane are molecules of chlorophyll , a pigment (a molecule that absorbs light) through which the entire process of photosynthesis begins. Chlorophyll is responsible for the green color of plants. The thylakoid membrane encloses an internal space called the thylakoid space. Other types of pigments are also involved in photosynthesis, but chlorophyll is by far the most important. As shown in Figure 5.7 , a stack of thylakoids is called a granum , and the space surrounding the granum is called stroma (not to be confused with stomata, the openings on the leaves).

Visual Connection

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

The Two Parts of Photosynthesis

Photosynthesis takes place in two stages: the light-dependent reactions and the Calvin cycle. In the light-dependent reactions , which take place at the thylakoid membrane, chlorophyll absorbs energy from sunlight and then converts it into chemical energy with the use of water. The light-dependent reactions release oxygen from the hydrolysis of water as a byproduct. In the Calvin cycle, which takes place in the stroma, the chemical energy derived from the light-dependent reactions drives both the capture of carbon in carbon dioxide molecules and the subsequent assembly of sugar molecules. The two reactions use carrier molecules to transport the energy from one to the other. The carriers that move energy from the light-dependent reactions to the Calvin cycle reactions can be thought of as “full” because they bring energy. After the energy is released, the “empty” energy carriers return to the light-dependent reactions to obtain more energy. The two-stage, two-location photosynthesis process was discovered by Joan Mary Anderson, whose continuing work over the subsequent decades provided much of our understanding of the process, the membranes, and the chemicals involved.

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• What is Photosynthesis

When you get hungry, you grab a snack from your fridge or pantry. But what can plants do when they get hungry? You are probably aware that plants need sunlight, water, and a home (like soil) to grow, but where do they get their food? They make it themselves!

Plants are called autotrophs because they can use energy from light to synthesize, or make, their own food source. Many people believe they are “feeding” a plant when they put it in soil, water it, or place it outside in the Sun, but none of these things are considered food. Rather, plants use sunlight, water, and the gases in the air to make glucose, which is a form of sugar that plants need to survive. This process is called photosynthesis and is performed by all plants, algae, and even some microorganisms. To perform photosynthesis, plants need three things: carbon dioxide, water, and sunlight.

Just like you, plants need to take in gases in order to live. Animals take in gases through a process called respiration. During the respiration process, animals inhale all of the gases in the atmosphere, but the only gas that is retained and not immediately exhaled is oxygen. Plants, however, take in and use carbon dioxide gas for photosynthesis. Carbon dioxide enters through tiny holes in a plant’s leaves, flowers, branches, stems, and roots. Plants also require water to make their food. Depending on the environment, a plant’s access to water will vary. For example, desert plants, like a cactus, have less available water than a lilypad in a pond, but every photosynthetic organism has some sort of adaptation, or special structure, designed to collect water. For most plants, roots are responsible for absorbing water. 

The last requirement for photosynthesis is an important one because it provides the energy to make sugar. How does a plant take carbon dioxide and water molecules and make a food molecule? The Sun! The energy from light causes a chemical reaction that breaks down the molecules of carbon dioxide and water and reorganizes them to make the sugar (glucose) and oxygen gas. After the sugar is produced, it is then broken down by the mitochondria into energy that can be used for growth and repair. The oxygen that is produced is released from the same tiny holes through which the carbon dioxide entered. Even the oxygen that is released serves another purpose. Other organisms, such as animals, use oxygen to aid in their survival. 

If we were to write a formula for photosynthesis, it would look like this: 

6CO 2 + 6H 2 O + Light energy → C 6 H 12 O 6 (sugar) + 6O 2 

The whole process of photosynthesis is a transfer of energy from the Sun to a plant. In each sugar molecule created, there is a little bit of the energy from the Sun, which the plant can either use or store for later. 

Imagine a pea plant. If that pea plant is forming new pods, it requires a large amount of sugar energy to grow larger. This is similar to how you eat food to grow taller and stronger. But rather than going to the store and buying groceries, the pea plant will use sunlight to obtain the energy to build sugar. When the pea pods are fully grown, the plant may no longer need as much sugar and will store it in its cells. A hungry rabbit comes along and decides to eat some of the plant, which provides the energy that allows the rabbit to hop back to its home. Where did the rabbit’s energy come from? Consider the process of photosynthesis. With the help of carbon dioxide and water, the pea pod used the energy from sunlight to construct the sugar molecules. When the rabbit ate the pea pod, it indirectly received energy from sunlight, which was stored in the sugar molecules in the plant. 

Humans, other animals, fungi, and some microorganisms cannot make food in their own bodies like autotrophs, but they still rely on photosynthesis. Through the transfer of energy from the Sun to plants, plants build sugars that humans consume to drive our daily activities. Even when we eat things like chicken or fish, we are transferring energy from the Sun into our bodies because, at some point, one organism consumed a photosynthetic organism (e.g., the fish ate algae). So the next time you grab a snack to replenish your energy, thank the Sun for it! 

This is an excerpt from the  Structure and Function  unit of our curriculum product line, Science and Technology Concepts TM  (STC). Please visit our publisher,  Carolina Biological , to learn more. 

[BONUS FOR TEACHERS] Watch "Photosynthesis: Blinded by the Light" to explore student misconceptions about matter and energy in photosynthesis and strategies for eliciting student ideas to address or build on them.

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Middle school biology - NGSS

Course: middle school biology - ngss   >   unit 3, photosynthesis in organisms.

• Understand: photosynthesis in organisms
• Apply: photosynthesis in organisms

Key points:

• Many organisms make their own food through photosynthesis . Plants, algae, and some unicellular organisms do photosynthesis.
• Photosynthesis is powered by energy from sunlight. This energy is used to rearrange atoms in carbon dioxide and water to make oxygen and sugars.
• Carbon dioxide and water are inputs of photosynthesis. These inputs come from the environment.
• The oxygen is released into the environment.
• The sugars can provide chemical energy . This energy can be used by the organism to live and grow. The sugars can also be used to build the organism’s structures, or they can be stored for later use.
• Photosynthesis is usually carried out in chloroplasts . Chloroplasts are cell structures that contain molecules called chlorophyll . Chlorophyll helps capture light energy.

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What Is the Final Product of Photosynthesis? Protein Starch Fat Mineral Salt

The correct option is b starch the correct option is b the explanation for the correct option: green plants are naturally autotrophic. they may produce their own food through the photosynthesis process. in the presence of chlorophyll pigment, the plant uses sunlight energy to manufacture food from carbon dioxide and water. glucose and oxygen are the end products of photosynthesis. a polysaccharide of glucose monomers is starch. plants store their food in the form of starch, which they produce through photosynthesis. the explanation for the incorrect option: option a: proteins are the polymer of amino acids. they are end products of translation. it helps in wound healing, growth, and development. option c: fats are made up of fatty acids and glycerol. it is one macromolecule and provides energy to the body. fats are high molecular weight and stored in the body. option d: micronutrients are nutrients that plants require in minute amounts. among them are micronutrients including boron, iron, chlorine, and molybdenum, to name a few. mineral salt absorption is normally accomplished by the application of metabolic energy. the active absorption of minerals is the name for this process. final answer: the final product of photosynthesis starch..

What is the end product of photosynthesis

Photosynthesis, Key to Life on Earth, Starts with a Single Photon

Using a complex cast of metal-studded pigments, proteins, enzymes, and co-enzymes, photosynthetic organisms can convert the energy in light into the chemical energy for life. And now, thanks to  a study published today in  Nature , we know that this organic chemical reaction is sensitive to the smallest quantity of light possible – a single photon.

The discovery solidifies our current understanding of photosynthesis and will help answer questions about how life works on the smallest of scales, where quantum physics and biology meet.

“A huge amount of work, theoretically and experimentally, has been done around the world trying to understand what happens after a photon is absorbed. But we realized that nobody was talking about the first step. That was still a question that needed to be answered in detail,” said co-lead author Graham Fleming, a senior faculty scientist in the Biosciences Area at Lawrence Berkeley National Laboratory (Berkeley Lab) and professor of chemistry at UC Berkeley.

In their study, Fleming, co-lead author Birgitta Whaley, a senior faculty scientist in the Energy Sciences Area at Berkeley Lab, and their research groups showed that a single photon can indeed initiate the first step of photosynthesis in photosynthetic purple bacteria. Because all photosynthetic organisms use similar processes and share an evolutionary ancestor, the team is confident that photosynthesis in plants and algae works the same way. “Nature invented a very clever trick,” Fleming said.

How living systems use light

Based on how efficient photosynthesis is at converting sunlight into energy-rich molecules, scientists have long assumed that a single photon was all it took to initiate the reaction, wherein photons pass energy to electrons that then trade places with electrons in different molecules, eventually creating the precursor ingredients for the production of sugars. After all, the sun doesn’t provide that many photons – only a thousand photons arrive at a single chlorophyll molecule per second on a sunny day – yet the process occurs reliably across the planet.

However, “no one had ever backed up that assumption with a demonstration,” said first author Quanwei Li, a joint postdoctoral researcher who develops new experimental techniques with quantum light in the Fleming and Whaley groups.

And, further complicating matters, a great deal of the research that has unraveled precise details about later steps of photosynthesis was performed by triggering photosynthetic molecules with powerful, ultra-fast laser pulses.

“There’s a huge difference in intensity between a laser and sunlight – a typical focused laser beam is a million times brighter than sunlight,” said Li. Even if you manage to produce a weak beam with an intensity matching that of sunlight, they are still very different due to quantum properties of light called photon statistics. Since no one has seen the photon get absorbed, we don’t know what difference it makes what kind of photon it is, he explained.

“But just like you need to understand each particle to build a quantum computer, we need to study the quantum properties of living systems to truly understand them, and to make efficient artificial systems that generate renewable fuels.” – Quanwei Li

Photosynthesis, like other chemical reactions, was first understood in bulk – meaning that we knew what the overall inputs and outputs were, and from that we could infer what interactions between individual molecules might look like. In the 1970s and 80s, advances in technology allowed scientists to directly study individual chemicals during reactions. Now, scientists are beginning to  explore the next frontier , the individual atom and subatomic particle scale, using even more advanced technologies.

From assumption to fact

Designing an experiment that would allow for observation of individual photons meant bringing together a unique team of theorists and experimentalists who combined cutting-edge tools from quantum optics and biology. “It was new for people who study photosynthesis, because they don’t normally use these tools, and it was new for people in quantum optics because we don’t normally think about applying these techniques to complex biological systems,” said Whaley, who is also a professor of chemical physics at UC Berkeley.

The scientists set up a photon source that generates a single pair of photons through a process called spontaneous parametric down-conversion. During each pulse, the first photon – “the herald” – was observed with a highly sensitive detector, which confirmed that the second photon was on its way to the assembled sample of light absorbing molecular structures taken from photosynthetic bacteria. Another photon detector near the sample was set up to measure the lower-energy photon that is emitted by the photosynthetic structure after it absorbed the second “heralded” photon of the original pair.  

The light absorbing structure used in the experiment, called the LH2, has been studied extensively. It is known that photons at the 800 nanometer (nm) wavelength get absorbed by a ring of 9 bacteriochlorophyll molecules in LH2, causing energy to be passed to a second ring of 18 bacteriochlorophyll molecules which can emit fluorescent photons at 850 nm. In the native bacteria, the energy from the photons would continue transferring to subsequent molecules until it is used to initiate the chemistry of photosynthesis. But in the experiment, when the LH2s had been separated from other cellular machinery, the detection of the 850 nm photon served as definitive sign that the process had been activated.  

“If you’ve only got one photon, it’s awfully easy to lose it. So that was the fundamental difficulty in this experiment and that’s why we use the herald photon,” said Fleming. The scientists analyzed more than 17.7 billion herald photon detection events and 1.6 million heralded fluorescent photon detection events to ensure that the observations could only be attributed to single-photon absorption, and that no other factors were influencing the results.

“I think the first thing is that this experiment has shown that you can actually do things with individual photons. So that’s a very, very important point,” said Whaley. “The next thing is, what else can we do? Our goal is to study the energy transfer from individual photons through the photosynthetic complex at the shortest possible temporal and spatial scales.”

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