overall summary equation for photosynthesis

The Balanced Chemical Equation for Photosynthesis

Photosynthesis Overall Chemical Reaction

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Photosynthesis is the process in plants and certain other organisms that uses the energy from the sun to convert carbon dioxide and water into glucose (a sugar) and oxygen.

Here is the balanced equation for the overall reaction:

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

Where: CO 2  = carbon dioxide   H 2 O = water light is required C 6 H 12 O 6  = glucose O 2  = oxygen

Explanation

In words, the equation may be stated as: Six carbon dioxide molecules and six water molecules react to produce one glucose molecule and six oxygen molecules .

The reaction requires energy in the form of light to overcome the activation energy needed for the reaction to proceed. Carbon dioxide and water don't spontaneously convert into glucose and oxygen .

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Photosynthesis

Reviewed by: BD Editors

Photosynthesis Definition

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

Photosynthesis Equation

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

Stages of Photosynthesis

The light reactions.

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

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

The Calvin Cycle

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

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

Products of Photosynthesis

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

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

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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.

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• BCcampus Open Publishing - Concepts of Biology – 1st Canadian Edition - Overview of Photosynthesis
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• 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.

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.

Photosynthesis – Equation, Formula & Products

Core concepts.

In this tutorial, you will learn all about photosynthesis . We begin with an introduction to photosynthesis and its balanced chemical equation. Then, we analyze the two key stages involved in this process and take a look at the final products. Lastly, we consider the different types of photosynthesis.

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Introduction to Photosynthesis

The process by which plants and other organisms convert light energy (sunlight) into chemical energy (glucose) is known as photosynthesis. Sunlight powers a series of reactions that use water and carbon dioxide to synthesize glucose and release oxygen as a byproduct. Energy is stored in the chemical bonds of glucose and can be later harvested to fuel the organism’s activities through cellular respiration or fermentation .

Photosynthesis is an endergonic process because it requires an input of energy from the surroundings in order for a chemical change to take place. Furthermore, photosynthesis is a reduction-oxidation (redox) reaction , meaning that it involves the transfer of electrons between chemical species. During the process, carbon dioxide is reduced (i.e., gains electrons) to form glucose, and water is oxidized (i.e., loses electrons) to form molecular oxygen.

The complex process of photosynthesis takes place in chloroplasts (i.e., membrane-bound organelles in plant and algal cells). Chloroplasts have an outer membrane and an inner membrane. The stroma is the fluid-filled space within the inner membrane; it surrounds flattened sac-like structures known as thylakoids. Thylakoids consist of a thylakoid space (lumen) surrounded by a thylakoid membrane. The thylakoid membrane contains photosystems, which are large complexes of proteins and pigments. There are two types of photosystems: photosystem I (PSI) and photosystem II (PSII).

Chemical Equation for Photosynthesis

The overall balanced equation for photosynthesis is commonly written as 6 CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6 O 2 (shown below). In other words, six molecules of carbon dioxide and six molecules of water react in the presence of sunlight to produce one molecule of glucose (a six-carbon sugar) and six molecules of oxygen. 

Stages of Photosynthesis

There are two main stages of photosynthesis: the light-dependent reactions and the Calvin cycle.

Light-Dependent Reactions

The light-dependent reactions use light energy to make ATP (an energy-carrying molecule) and NADPH (an electron carrier) for use in the Calvin cycle. In addition, oxygen is released as a result of the oxidation of water. In plants and algae, the light-dependent reactions take place in the thylakoid membrane of chloroplasts. The most common form of the light-dependent reactions is a process known as non-cyclic photophosphorylation. This process involves two key steps: ATP synthesis (via photosystem II) and NADPH synthesis (via photosystem I).

• Step 1 (ATP Synthesis): Pigments in photosystem II (such as chlorophylls) absorb light and energize electrons. A proton gradient is formed as these excited electrons travel down an electron transport chain and release energy that pumps hydrogen ions from the stroma to the thylakoid lumen. The splitting of water molecules through photolysis produces hydrogen ions (as well as oxygen molecules) that further contribute to this electrochemical gradient. As hydrogen ions flow down their gradient (i.e., back across the thylakoid membrane and into the stroma), they travel through an enzyme known as ATP synthase. ATP synthase catalyzes the formation of adenosine triphosphate (ATP) using ADP (adenosine diphosphate) and inorganic phosphate (P i ).
• Step 2 (NADPH Synthesis): Electrons are transferred to photosystem I and energized by the light absorbed by PSI pigments. The electrons reach the end of the electron transport chain and are passed to an enzyme known as ferredoxin-NADP + reductase (FNR). FNR catalyzes the reaction by which NADP + is reduced to NADPH.

Calvin Cycle

The Calvin cycle (also referred to as the light-independent reactions) takes place in the stroma of chloroplasts and is not directly dependent on sunlight. Instead, this stage utilizes the products of the light-dependent reactions (ATP and NADPH), along with carbon dioxide, to synthesize glucose. The Calvin cycle consists of three basic steps: carbon fixation, reduction, and regeneration.

• Step 1 (Carbon Fixation): RuBisCO (the most abundant enzyme on Earth) catalyzes the carboxylation of ribulose-1,5-biphosphate (RuBP) by carbon dioxide to produce an unstable six-carbon compound. This six-carbon compound is then readily converted into two molecules of 3-phosphoglyceric acid (3-PGA).
• Step 2 (Reduction): An enzyme known as phosphoglycerate kinase catalyzes the phosphorylation of 3-PGA by ATP to produce 1,3-biphosphoglyceric acid (1,3-BPG) and ADP. Next, another enzyme (glyceraldehyde 3-phosphate dehydrogenase) catalyzes the reduction of 1,3-BPG by NADPH to produce glyceraldehyde 3-phosphate (G3P) and NADP + .
• Step 3 (Regeneration): Every turn of the Calvin cycle produces two molecules of G3P. Therefore, six turns of the cycle produce twelve molecules of G3P. Two of these G3P molecules exit the cycle and are used to synthesize one molecule of glucose. Meanwhile, the other ten molecules of G3P remain in the cycle and are used to regenerate six RuBP molecules. The regeneration of RuBP requires ATP, but it allows the cycle to continue.

Products of Photosynthesis

The major product of photosynthesis is glucose, a simple sugar with the molecular formula C 6 H 12 O 6 . Plants and other photosynthetic organisms use glucose for numerous functions, including those listed below.

• Cellular Respiration: Glucose is broken down in order to produce ATP (which can be used to fuel other cellular activities) through a process known as cellular respiration.
• Biosynthesis of Starch and Cellulose: Glucose molecules can be linked together to form complex carbohydrates such as starch and cellulose. Plants and other organisms use starch to store energy and cellulose to support/rigidify their cell walls.
• Protein Synthesis: Glucose can be combined with nitrates (from the soil) to produce amino acids, which can then be used to build proteins.

In addition, oxygen is released into the atmosphere during the process of photosynthesis. Plants (along with many other organisms) use oxygen to carry out aerobic respiration.

Types of Photosynthesis

There are three main types of photosynthesis: C3, C4, and CAM (crassulacean acid metabolism). They differ in the way that they manage photorespiration, a wasteful process that occurs when the enzyme rubisco acts on oxygen instead of carbon dioxide. Photorespiration competes with the Calvin cycle and decreases the efficiency of photosynthesis (by wasting energy and using up fixed carbon).

C3 Photosynthesis

The majority of plants use C3 photosynthesis, a process in which no special features or adaptations are used to combat photorespiration. Hot, dry climates are not ideal for C3 plants (e.g., rice, wheat, and barley) because of the increased rate of photorespiration, which is due to the buildup of oxygen that occurs when plants close their stomata (leaf pores) in order to prevent water loss.

C4 Photosynthesis

C4 photosynthesis reduces photorespiration by performing the initial carbon dioxide fixation and Calvin cycle in two different cell types. This process utilizes an additional enzyme known as phosphoenolpyruvate (PEP) carboxylase. PEP carboxylase does not react with oxygen (unlike rubisco) and is able to catalyze a reaction between carbon dioxide and PEP in the mesophyll cells to produce the intermediate four-carbon compound oxaloacetate. Oxaloacetate is then reduced to malate and transported to bundle sheath cells. In these cells, malate undergoes decarboxylation, forming a special compartment for the concentration of carbon dioxide around rubisco.

As a result, the Calvin cycle can proceed as normal, and an opportunity for rubisco to bind to oxygen is prevented. C4 plants (e.g., maize and sugarcane) have a competitive advantage over C3 plants in hot, dry environments where the benefits of reduced photorespiration outweigh the additional energy costs associated with C4 photosynthesis.

CAM Photosynthesis

Crassulacean acid metabolism, also known as CAM photosynthesis, reduces photorespiration by performing the initial carbon dioxide fixation and Calvin cycle at separate times. CAM plants (e.g., cactus and pineapple) open their stomata at night, allowing carbon dioxide to enter the leaf. The carbon dioxide is converted to oxaloacetate by PEP carboxylase, the same enzyme used in C4 photosynthesis. Oxaloacetate is subsequently reduced to malate, which is stored as malic acid in vacuoles .

During the day (when light is readily available), CAM plants close their stomata and prepare for the Calvin cycle. Malate is transported into chloroplasts and broken down to release carbon dioxide, which is heavily concentrated around the enzyme rubisco. Similar to C4 photosynthesis, crassulacean acid metabolism is an energetically expensive process. However, it is quite useful for plants in hot, arid climates that need to minimize photorespiration and conserve water.

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Photosynthesis Equation: What Is It? How Does It Work?

General Education

The word photosynthesis comes from two Greek words: photo, meaning “light”, and synthesis, meaning “put together.” Looking at that those two roots, we have a good idea of what happens during the chemical process of photosynthesis: plants put together water and carbon dioxide with light to create glucose and oxygen.

In this article, we’ll break down what photosynthesis is, why photosynthesis is important, and discuss the chemical equation for photosynthesis: what it is and what each part of it means.

What Is Photosynthesis?

Put simply, photosynthesis is how plants, algae, and certain types of bacteria harness energy from sunlight to create chemical energy for themselves to live.

There are two main types of photosynthesis: oxygenic photosynthesis and anoxygenic photosynthesis. Oxygenic photosynthesis is more common—that’s the type we see in plants and algae. Anoxygenic photosynthesis mainly occurs in bacteria.

In oxygenic photosynthesis, plants use light energy to combine carbon dioxide (CO2) and water (H2O). This chemical reaction produces carbohydrates for the plants to consume and oxygen, which is released back into the air.

Anoxygenic photosynthesis is very similar, but it doesn’t produce oxygen. We’ll be focusing on the more common type of photosynthesis, oxygenic photosynthesis, for the rest of this article.

Why Is Photosynthesis Important?

Photosynthesis is important for a few reasons:

First, it produces energy that plants need to live. The resulting carbohydrates provide plants with the energy to grow and live.

Second, photosynthesis helps take in the carbon dioxide produced by breathing organisms and convert that into oxygen, which is then reintroduced back into the atmosphere. Basically, with photosynthesis, plants are helping produce the oxygen that all living things need to breathe and survive.

Photosynthesis Equation

Here is the chemical equation for photosynthesis:

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

Photosynthesis Formula Breakdown

Now that we know what the photosynthesis equation is, let’s break down each piece of the photosynthesis formula.

On the reactants side, we have:

6CO2 = Six molecules of carbon dioxide

12H2O = Twelve molecules of water

Light Energy = Light from the sun

On the products side, we have:

C6H12O6 = glucose

6O2 = six molecules of oxygen

6H2O = six molecules of water

As we learned earlier, the glucose will be used by the plant as energy. The oxygen and water will be released back into the atmosphere to help other living things.

What You Need to Know About the Photosynthesis Formula

During photosynthesis, plants use light energy to combine carbon dioxide and water to produce glucose, oxygen, and water.

Photosynthesis is important because it provides plants with the energy they need to survive. It also releases needed oxygen and water back into the atmosphere.

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• Biology Article

Photosynthesis

Photosynthesis is a process by which phototrophs convert light energy into chemical energy, which is later used to fuel cellular activities. The chemical energy is stored in the form of sugars, which are created from water and carbon dioxide.

Table of Contents

• What is Photosynthesis?
• Site of photosynthesis

What Is Photosynthesis in Biology?

The word “ photosynthesis ” is derived from the Greek words  phōs  (pronounced: “fos”) and σύνθεσις (pronounced: “synthesis “) Phōs means “light” and σύνθεσις   means, “combining together.” This means “ combining together with the help of light .”

Photosynthesis also applies to other organisms besides green plants. These include several prokaryotes such as cyanobacteria, purple bacteria and green sulfur bacteria. These organisms exhibit photosynthesis just like green plants.The glucose produced during photosynthesis is then used to fuel various cellular activities. The by-product of this physio-chemical process is oxygen.

A visual representation of the photosynthesis reaction

• Photosynthesis is also used by algae to convert solar energy into chemical energy. Oxygen is liberated as a by-product and light is considered as a major factor to complete the process of photosynthesis.
• Photosynthesis occurs when plants use light energy to convert carbon dioxide and water into glucose and oxygen. Leaves contain microscopic cellular organelles known as chloroplasts.
• Each chloroplast contains a green-coloured pigment called chlorophyll. Light energy is absorbed by chlorophyll molecules whereas carbon dioxide and oxygen enter through the tiny pores of stomata located in the epidermis of leaves.
• Another by-product of photosynthesis is sugars such as glucose and fructose.
• These sugars are then sent to the roots, stems, leaves, fruits, flowers and seeds. In other words, these sugars are used by the plants as an energy source, which helps them to grow. These sugar molecules then combine with each other to form more complex carbohydrates like cellulose and starch. The cellulose is considered as the structural material that is used in plant cell walls.

Where Does This Process Occur?

Chloroplasts are the sites of photosynthesis in plants and blue-green algae.  All green parts of a plant, including the green stems, green leaves,  and sepals – floral parts comprise of chloroplasts – green colour plastids. These cell organelles are present only in plant cells and are located within the mesophyll cells of leaves.

Also Read:  Photosynthesis Early Experiments

Photosynthesis Equation

Photosynthesis reaction involves two reactants, carbon dioxide and water. These two reactants yield two products, namely, oxygen and glucose. Hence, the photosynthesis reaction is considered to be an endothermic reaction. Following is the photosynthesis formula:

Unlike plants, certain bacteria that perform photosynthesis do not produce oxygen as the by-product of photosynthesis. Such bacteria are called anoxygenic photosynthetic bacteria. The bacteria that do produce oxygen as a by-product of photosynthesis are called oxygenic photosynthetic bacteria.

Structure Of Chlorophyll

The structure of Chlorophyll consists of 4 nitrogen atoms that surround a magnesium atom. A hydrocarbon tail is also present. Pictured above is chlorophyll- f,  which is more effective in near-infrared light than chlorophyll- a

Chlorophyll is a green pigment found in the chloroplasts of the  plant cell   and in the mesosomes of cyanobacteria. This green colour pigment plays a vital role in the process of photosynthesis by permitting plants to absorb energy from sunlight. Chlorophyll is a mixture of chlorophyll- a  and chlorophyll- b .Besides green plants, other organisms that perform photosynthesis contain various other forms of chlorophyll such as chlorophyll- c1 ,  chlorophyll- c2 ,  chlorophyll- d and chlorophyll- f .

Also Read:   Biological Pigments

Process Of Photosynthesis

At the cellular level,  the photosynthesis process takes place in cell organelles called chloroplasts. These organelles contain a green-coloured pigment called chlorophyll, which is responsible for the characteristic green colouration of the leaves.

As already stated, photosynthesis occurs in the leaves and the specialized cell organelles responsible for this process is called the chloroplast. Structurally, a leaf comprises a petiole, epidermis and a lamina. The lamina is used for absorption of sunlight and carbon dioxide during photosynthesis.

Structure of Chloroplast. Note the presence of the thylakoid

“Photosynthesis Steps:”

• During the process of photosynthesis, carbon dioxide enters through the stomata, water is absorbed by the root hairs from the soil and is carried to the leaves through the xylem vessels. Chlorophyll absorbs the light energy from the sun to split water molecules into hydrogen and oxygen.
• The hydrogen from water molecules and carbon dioxide absorbed from the air are used in the production of glucose. Furthermore, oxygen is liberated out into the atmosphere through the leaves as a waste product.
• Glucose is a source of food for plants that provide energy for  growth and development , while the rest is stored in the roots, leaves and fruits, for their later use.
• Pigments are other fundamental cellular components of photosynthesis. They are the molecules that impart colour and they absorb light at some specific wavelength and reflect back the unabsorbed light. All green plants mainly contain chlorophyll a, chlorophyll b and carotenoids which are present in the thylakoids of chloroplasts. It is primarily used to capture light energy. Chlorophyll-a is the main pigment.

The process of photosynthesis occurs in two stages:

• Light-dependent reaction or light reaction
• Light independent reaction or dark reaction

Stages of Photosynthesis in Plants depicting the two phases – Light reaction and Dark reaction

Light Reaction of Photosynthesis (or) Light-dependent Reaction

• Photosynthesis begins with the light reaction which is carried out only during the day in the presence of sunlight. In plants, the light-dependent reaction takes place in the thylakoid membranes of chloroplasts.
• The Grana, membrane-bound sacs like structures present inside the thylakoid functions by gathering light and is called photosystems.
• These photosystems have large complexes of pigment and proteins molecules present within the plant cells, which play the primary role during the process of light reactions of photosynthesis.
• There are two types of photosystems: photosystem I and photosystem II.
• Under the light-dependent reactions, the light energy is converted to ATP and NADPH, which are used in the second phase of photosynthesis.
• During the light reactions, ATP and NADPH are generated by two electron-transport chains, water is used and oxygen is produced.

The chemical equation in the light reaction of photosynthesis can be reduced to:

2H 2 O + 2NADP+ + 3ADP + 3Pi → O 2 + 2NADPH + 3ATP

Dark Reaction of Photosynthesis (or) Light-independent Reaction

• Dark reaction is also called carbon-fixing reaction.
• It is a light-independent process in which sugar molecules are formed from the water and carbon dioxide molecules.
• The dark reaction occurs in the stroma of the chloroplast where they utilize the NADPH and ATP products of the light reaction.
• Plants capture the carbon dioxide from the atmosphere through stomata and proceed to the Calvin photosynthesis cycle.
• In the Calvin cycle , the ATP and NADPH formed during light reaction drive the reaction and convert 6 molecules of carbon dioxide into one sugar molecule or glucose.

The chemical equation for the dark reaction can be reduced to:

3CO 2 + 6 NADPH + 5H 2 O + 9ATP → G3P + 2H+ + 6 NADP+ + 9 ADP + 8 Pi

* G3P – glyceraldehyde-3-phosphate

Calvin photosynthesis Cycle (Dark Reaction)

Also Read:  Cyclic And Non-Cyclic Photophosphorylation

Importance of Photosynthesis

• Photosynthesis is essential for the existence of all life on earth. It serves a crucial role in the food chain – the plants create their food using this process, thereby, forming the primary producers.
• Photosynthesis is also responsible for the production of oxygen – which is needed by most organisms for their survival.

Frequently Asked Questions

1. what is photosynthesis explain the process of photosynthesis., 2. what is the significance of photosynthesis, 3. list out the factors influencing photosynthesis., 4. what are the different stages of photosynthesis, 5. what is the calvin cycle, 6. write down the photosynthesis equation..

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Please What Is Meant By 300-400 PPM

PPM stands for Parts-Per-Million. It corresponds to saying that 300 PPM of carbon dioxide indicates that if one million gas molecules are counted, 300 out of them would be carbon dioxide. The remaining nine hundred ninety-nine thousand seven hundred are other gas molecules.

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