the end products of photosynthesis include

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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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Photosynthesis

1. Photosynthesis is the process plants use to make their own food.

Like all living things, plants need energy to carry out the processes that keep them alive. They get this energy from food. Humans and most other animals are heterotrophs, meaning we have to consume other organisms—plants, other animals, or some combination of the two—for food. However, plants are autotrophs, meaning they create their own food.

Plants use sunlight to convert water and carbon dioxide into glucose and oxygen in a process called photosynthesis . In biology, this information is often expressed using a chemical equation .

Chemical equations typically show the molecules that enter the reaction (the reactants ) to the left and the molecules that result from the reaction (the products ) to the right, separated by an arrow that indicates a reaction taking place.

[Reactants] → [Products]

You can think of the reactants as the ingredients for preparing a meal and the products as the different dishes in that meal.

With that in mind, let’s take a look at the chemical equation for photosynthesis:

Sunlight + 6 CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6 O 2 CO 2 = carbon dioxide H 2 O = water C 6 H 12 O 6 = glucose O 2 = oxygen * Sometimes, you’ll see sunlight, or a symbol indicating the sun, over the arrow in the equation.

Therefore, to produce one molecule of glucose (and 6 molecules of oxygen gas), a plant needs 6 molecules of carbon dioxide and 6 molecules of water.

2. The reactants of photosynthesis are carbon dioxide and water.

We’ve established that plants need carbon dioxide (CO 2 ) and water (H 2 O) to produce their food, but where do these reactants come from and how do they get where they need to go inside the plant?

Plants take in carbon dioxide from the air through small openings in their leaves called stomata. Some plants (most monocots) have stomata on both sides of their leaves, and others (dicots and a few monocots) only have stomata on the underside, or lower epidermis.

Plants get water from the soil surrounding their roots, and water gets to the leaves by traveling through the xylem, part of the plant’s vascular system. In leaves, the xylem and phloem are contained in the vascular bundle.

Once inside the leaf, the carbon dioxide and water molecules move into the cells of the mesophyll, the layer of ground tissue between the upper and lower epidermis. Within these cells, organelles called chloroplasts use the carbon dioxide and water to carry out photosynthesis.

3. Light energy from the sun initiates photosynthesis in the chloroplasts of plant cells.

Plant cells have special organelles called chloroplasts, which serve as the sites for the reactions that make up photosynthesis. Their thylakoid membranes contain a pigment called chlorophyll, which absorbs photons (light energy) from the sun, initiating the light-dependent reactions that take place within the thylakoids.

During these reactions, water molecules (H 2 O) are broken down. NADPH and ATP—high energy molecules that power the production of glucose—are produced during the light-dependent reactions, as well. Electrons and hydrogen ions from the water are used to build NADPH. Hydrogen ions also power the conversion of ADP to ATP.

4. The products of photosynthesis are glucose and oxygen.

Did you know that oxygen is actually a waste product of photosynthesis? Although the hydrogen atoms from the water molecules are used in the photosynthesis reactions, the oxygen molecules are released as oxygen gas (O 2 ). (This is good news for organisms like humans and plants that use oxygen to carry out cellular respiration!) Oxygen passes out of the leaves through the stomata.

The light-independent reactions of photosynthesis—also known as the Calvin cycle—use enzymes in the stroma, along with the energy-carrying molecules (ATP and NADPH) from the light-dependent reactions, to break down carbon dioxide molecules (CO 2 ) into a form that is used to build glucose.The mitochondria in the plant’s cells use cellular respiration to break glucose down into a usable form of energy (ATP), which fuels all the plant’s activities.

After the light-independent reactions, glucose is often made into larger sugars like sucrose or carbohydrates like starch or cellulose. Sugars leave the leaf through the phloem and can travel to the roots for storage or to other parts of the plant, where they’re used as energy to fuel the plant’s activities.

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What Are the Products of Photosynthesis?

Result of Photosynthesis in Plants

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

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

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

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

Key Takeaways

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

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

Intermediate Products of Photosynthesis

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

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

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

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

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

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

Factors That Affect the Rate of Photosynthesis

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

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

What Is Not a Product of Photosynthesis?

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

• Bidlack, J.E.; Stern, K.R.; Jansky, S. (2003). Introductory Plant Biology . New York: McGraw-Hill. ISBN 978-0-07-290941-8.
• Blankenship, R.E. (2014). Molecular Mechanisms of Photosynthesis (2nd ed.). John Wiley & Sons. ISBN 978-1-4051-8975-0.
• Reece J.B., et al. (2013). Campbell Biology . Benjamin Cummings. ISBN 978-0-321-77565-8.
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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.

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Basic products of photosynthesis

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

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

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

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

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

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

Factors that influence the rate of photosynthesis

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

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

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

The process

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

Chlorophyll

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

Light-dependent Reactions vs. Light-independent Reactions

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

C3 and C4 Photosynthesis

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

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Related Resources

• 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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Module 6: Metabolic Pathways

An overview of photosynthesis, learning outcomes.

• Identify the reactants and products of photosynthesis

Photosynthesis is a multi-step process that requires sunlight, carbon dioxide (which is low in energy), and water as substrates (Figure 1). After the process is complete, it releases oxygen and produces glyceraldehyde-3-phosphate (GA3P), simple carbohydrate molecules (which are high in energy) that can subsequently be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy and the energized carbon that all living things need to survive.

Figure 1. Photosynthesis uses solar energy, carbon dioxide, and water to produce energy-storing carbohydrates. Oxygen is generated as a waste product of photosynthesis.

The following is the chemical equation for photosynthesis (Figure 2):

Figure 2. The basic equation for photosynthesis is deceptively simple. In reality, the process takes place in many steps involving intermediate reactants and products. Glucose, the primary energy source in cells, is made from two three-carbon GA3Ps.

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

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. 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 in the mesophyll. Chloroplasts have a double membrane envelope (composed of an outer membrane and an inner membrane). 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 3, 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).

Practice Question

Figure 3. Photosynthesis takes place in chloroplasts, which have an outer membrane and an inner membrane. Stacks of thylakoids called grana form a third membrane layer.

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

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 drive 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, 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 4 illustrates the components inside the chloroplast where the light-dependent and light-independent reactions take place.

Figure 4. Photosynthesis takes place in two stages: light dependent reactions and the Calvin cycle. Light-dependent reactions, which take place in the thylakoid membrane, use light energy to make ATP and NADPH. The Calvin cycle, which takes place in the stroma, uses energy derived from these compounds to make GA3P from CO 2 .

Photosynthesis at the Grocery Store

Figure 5. Foods that humans consume originate from photosynthesis. (credit: Associação Brasileira de Supermercados)

Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle (Figure 5) contains hundreds, if not thousands, of different products for customers to buy and consume.

Although there is a large variety, each item links 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) can be derived from algae or from oil, the fossilized remains of photosynthetic organisms. 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.

In Summary: An Overview of Photosynthesis

The process of photosynthesis transformed life on Earth. By harnessing energy from the sun, photosynthesis evolved to allow 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, called photoautotrophs, can perform photosynthesis; they require the presence of chlorophyll, a specialized pigment that absorbs certain portions 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 waste product 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.

• Biology 2e. Provided by : OpenStax. Located at : http://cnx.org/contents/[email protected] . License : CC BY: Attribution . License Terms : Access for free at https://openstax.org/books/biology-2e/pages/1-introduction

5.2 The Light-Dependent Reactions of Photosynthesis

Learning objectives.

• Explain how plants absorb energy from sunlight
• Describe how the wavelength of light affects its energy and color
• Describe how and where photosynthesis takes place within a plant

How can light be used to make food? It is easy to think of light as something that exists and allows living organisms, such as humans, to see, but light is a form of energy. Like all energy, light can travel, change form, and be harnessed to do work. In the case of photosynthesis, light energy is transformed into chemical energy, which autotrophs use to build carbohydrate molecules. However, autotrophs only use a specific component of sunlight ( Figure 5.8 ).

Link to Learning

Watch the process of photosynthesis within a leaf in this video.

What Is Light Energy?

The sun emits an enormous amount of electromagnetic radiation (solar energy). Humans can see only a fraction of this energy, which is referred to as “visible light.” The manner in which solar energy travels can be described and measured as waves. Scientists can determine the amount of energy of a wave by measuring its wavelength , the distance between two consecutive, similar points in a series of waves, such as from crest to crest or trough to trough ( Figure 5.9 ).

Visible light constitutes only one of many types of electromagnetic radiation emitted from the sun. The electromagnetic spectrum is the range of all possible wavelengths of radiation ( Figure 5.10 ). Each wavelength corresponds to a different amount of energy carried.

Each type of electromagnetic radiation has a characteristic range of wavelengths. The longer the wavelength (or the more stretched out it appears), the less energy is carried. Short, tight waves carry the most energy. This may seem illogical, but think of it in terms of a piece of moving rope. It takes little effort by a person to move a rope in long, wide waves. To make a rope move in short, tight waves, a person would need to apply significantly more energy.

The sun emits ( Figure 5.10 ) a broad range of electromagnetic radiation, including X-rays and ultraviolet (UV) rays. The higher-energy waves are dangerous to living things; for example, X-rays and UV rays can be harmful to humans.

Absorption of Light

Light energy enters the process of photosynthesis when pigments absorb the light. In plants, pigment molecules absorb only visible light for photosynthesis. The visible light seen by humans as white light actually exists in a rainbow of colors. Certain objects, such as a prism or a drop of water, disperse white light to reveal these colors to the human eye. The visible light portion of the electromagnetic spectrum is perceived by the human eye as a rainbow of colors, with violet and blue having shorter wavelengths and, therefore, higher energy. At the other end of the spectrum toward red, the wavelengths are longer and have lower energy.

Understanding Pigments

Different kinds of pigments exist, and each absorbs only certain wavelengths (colors) of visible light. Pigments reflect the color of the wavelengths that they cannot absorb.

All photosynthetic organisms contain a pigment called chlorophyll a , which humans see as the common green color associated with plants. Chlorophyll a absorbs wavelengths from either end of the visible spectrum (blue and red), but not from green. Because green is reflected, chlorophyll appears green.

Other pigment types include chlorophyll b (which absorbs blue and red-orange light) and the carotenoids. Each type of pigment can be identified by the specific pattern of wavelengths it absorbs from visible light, which is its absorption spectrum .

Many photosynthetic organisms have a mixture of pigments; between them, the organism can absorb energy from a wider range of visible-light wavelengths. Not all photosynthetic organisms have full access to sunlight. Some organisms grow underwater where light intensity decreases with depth, and certain wavelengths are absorbed by the water. Other organisms grow in competition for light. Plants on the rainforest floor must be able to absorb any bit of light that comes through, because the taller trees block most of the sunlight ( Figure 5.11 ).

How Light-Dependent Reactions Work

The overall purpose of the light-dependent reactions is to convert light energy into chemical energy. This chemical energy will be used by the Calvin cycle to fuel the assembly of sugar molecules.

The light-dependent reactions begin in a grouping of pigment molecules and proteins called a photosystem . Photosystems exist in the membranes of thylakoids. A pigment molecule in the photosystem absorbs one photon , a quantity or “packet” of light energy, at a time.

A photon of light energy travels until it reaches a molecule of chlorophyll. The photon causes an electron in the chlorophyll to become “excited.” The energy given to the electron allows it to break free from an atom of the chlorophyll molecule. Chlorophyll is therefore said to “donate” an electron ( Figure 5.12 ).

To replace the electron in the chlorophyll, a molecule of water is split. This splitting releases an electron and results in the formation of oxygen (O 2 ) and hydrogen ions (H + ) in the thylakoid space. Technically, each breaking of a water molecule releases a pair of electrons, and therefore can replace two donated electrons.

The replacing of the electron enables chlorophyll to respond to another photon. The oxygen molecules produced as byproducts find their way to the surrounding environment. The hydrogen ions play critical roles in the remainder of the light-dependent reactions.

Keep in mind that the purpose of the light-dependent reactions is to convert solar energy into chemical carriers that will be used in the Calvin cycle. In eukaryotes and some prokaryotes, two photosystems exist. The first is called photosystem II, which was named for the order of its discovery rather than for the order of the function.

After the photon hits, photosystem II transfers the free electron to the first in a series of proteins inside the thylakoid membrane called the electron transport chain. As the electron passes along these proteins, energy from the electron fuels membrane pumps that actively move hydrogen ions against their concentration gradient from the stroma into the thylakoid space. This is quite analogous to the process that occurs in the mitochondrion in which an electron transport chain pumps hydrogen ions from the mitochondrial stroma across the inner membrane and into the intermembrane space, creating an electrochemical gradient. After the energy is used, the electron is accepted by a pigment molecule in the next photosystem, which is called photosystem I ( Figure 5.13 ).

Generating an Energy Carrier: ATP

In the light-dependent reactions, energy absorbed by sunlight is stored by two types of energy-carrier molecules: ATP and NADPH. The energy that these molecules carry is stored in a bond that holds a single atom or group of atoms to the molecule. For ATP, it is a phosphate group, and for NADPH, it is a hydrogen atom. Recall that NADH was a similar molecule that carried energy in the mitochondrion from the citric acid cycle to the electron transport chain. When these molecules release energy into the Calvin cycle, they each lose either atoms or groups of atoms to become the lower-energy molecules ADP and NADP + .

The buildup of hydrogen ions in the thylakoid space forms an electrochemical gradient because of the difference in the concentration of protons (H + ) and the difference in the charge across the membrane that they create. This potential energy is harvested and stored as chemical energy in ATP through chemiosmosis, the movement of hydrogen ions down their electrochemical gradient through the transmembrane enzyme ATP synthase, just as in the mitochondrion.

The hydrogen ions are allowed to pass through the thylakoid membrane through an embedded protein complex called ATP synthase. This same protein generated ATP from ADP in the mitochondrion. The energy generated by the hydrogen ion stream allows ATP synthase to attach a third phosphate to ADP, which forms a molecule of ATP in a process called photophosphorylation. The flow of hydrogen ions through ATP synthase is called chemiosmosis, because the ions move from an area of high to low concentration through a semi-permeable structure.

Generating Another Energy Carrier: NADPH

The remaining function of the light-dependent reaction is to generate the other energy-carrier molecule, NADPH. As the electron from the electron transport chain arrives at photosystem I, it is re-energized with another photon captured by chlorophyll. The energy from this electron drives the formation of NADPH from NADP + and a hydrogen ion (H + ). Now that the solar energy is stored in energy carriers, it can be used to make a sugar molecule.

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