what are the 2 end products of photosynthesis

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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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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Photosynthesis: Reactants and Products

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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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Basic products of photosynthesis

Evolution of the process, light intensity and temperature.

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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 ).

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What Are the Reactants & Products in the Equation for Photosynthesis?

Organelles Involved in Photosynthesis

Photosynthesis is the process by which plants, and some bacteria, use solar energy to produce sugar. This process converts light energy to chemical energy, which is stored in the sugars. This process is important for two reasons. First, photosynthesis provides the energy that is used by all other organisms to survive. Second, photosynthesis removes carbon dioxide from the atmosphere, replacing it with life-sustaining oxygen. The process involves three basic reactants and produces three key products.

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

The reactants for photosynthesis are light energy, water, carbon dioxide and chlorophyll, while the products are glucose (sugar), oxygen and water.

Photosynthesis Reactants

The photosynthetic process requires several simple reactants. Water is the first required reactant. The plant acquires water through its root system. The next required reactant is carbon dioxide. The plant absorbs this gas through its leaves. The final required reactant is light energy. The plant absorbs this energy through green pigments, called chlorophyll. This chlorophyll is located in the plant's chloroplasts.

Products of Photosynthesis

The photosynthetic process produces several products. The first product, and primary reason for the process, is simple sugar. This sugar, called glucose, is the end result of the conversion of solar energy to chemical energy. It represents stored energy that can be used by the plant, or consumed by other organisms. Oxygen is also a product of photosynthesis. This oxygen is released into the atmosphere through the plant’s leaves. Water is also a product of photosynthesis. This water is produced from the oxygen atoms in the carbon dioxide molecules. The oxygen molecules released into the atmosphere come exclusively from the original water molecules, not from the carbon dioxide molecules.

Light-Dependent Process

Photosynthesis is a two-stage process. The first stage is called the light-dependent process, or light reactions, because it requires sunlight. During this stage, light energy is converted into adenosine triphosphate (ATP) and NADPH. The ATP represents stored chemical energy. These products of the light reaction are then used by the plant during the second stage of the photosynthesis process.

Light-Independent Process

The second stage of the photosynthesis process is the light-independent process, or dark reactions. During this stage, the ATP and NADPH are used to break chemical bonds and form new ones. The bonds of the carbon dioxide molecules are broken; this allows the carbon atoms to be bonded to some of the water molecules to form glucose. The oxygen atoms from the carbon dioxide are bonded to free hydrogen atoms; this bonding produces water. The free oxygen atoms from the original water molecules are released to the atmosphere.

The Overall Process

When viewed as a whole, the photosynthetic process utilizes 12 water molecules, six carbon dioxide molecules and light energy to produce one glucose molecule, six water molecules and six oxygen molecules. This can be represented by the following chemical equation:

It is important to remember that the resulting oxygen is produced from the original water molecules, not the carbon dioxide. This distinction becomes important when considering anoxygenic photosynthesis.

Related Articles

How do plant cells obtain energy, what are light dependent reactions, what are light independent reactions, why is water important to photosynthesis, what happens in the light reaction of photosynthesis, what provides electrons for the light reactions, materials needed for photosynthesis, how does a plant convert light energy to chemical energy, phases of photosynthesis & its location, what is the end product of photosynthesis, when does respiration occur in plants, why do plants need the sun, difference between aerobic & anaerobic cellular respiration..., chemical ingredients of photosynthesis, what is the sun's role in photosynthesis, how oxygen gas is produced during photosynthesis, sequence stages in photosynthesis, what is nadph in photosynthesis, how does photosynthesis work in plants.

• University of Illinois at Urbana-Champaign; The Photosynthetic Process; John Whitmarsh, Ph.D., and Govindjee, Ph.D.

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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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8.2 The Light-Dependent Reaction of Photosynthesis

Learning objectives.

In this section, you will explore the following questions:

• How do plants absorb energy from sunlight?
• What are the differences between short and long wavelengths of light? What wavelengths are used in photosynthesis?
• How and where does photosynthesis occur within a plant?

Connection for AP ® Courses

Photosynthesis consists of two stages: the light-dependent reactions and the light-independent reactions or Calvin cycle. The light-dependent reactions occur when light is available. The overall equation for photosynthesis shows that is it a redox reaction; carbon dioxide is reduced and water is oxidized to produce oxygen:

The light-dependent reactions occur in the thylakoid membranes of chloroplasts, whereas the Calvin cycle occurs in the stroma of chloroplasts. Embedded in the thylakoid membranes are two photosystems (PS I and PS II), which are complexes of pigments that capture solar energy. Chlorophylls a and b absorb violet, blue, and red wavelengths from the visible light spectrum and reflect green. The carotenoid pigments absorb violet-blue-green light and reflect yellow-to-orange light. Environmental factors such as day length and temperature influence which pigments predominant at certain times of the year. Although the two photosystems run simultaneously, it is easier to explore them separately. Let’s begin with photosystem II.

A photon of light strikes the antenna pigments of PS II to initiate photosynthesis. In the noncyclic pathway, PS II captures photons at a slightly higher energy level than PS I. (Remember that shorter wavelengths of light carry more energy.) The absorbed energy travels to the reaction center of the antenna pigment that contains chlorophyll a and boosts chlorophyll a electrons to a higher energy level. The electrons are accepted by a primary electron acceptor protein and then pass to the electron transport chain also embedded in the thylakoid membrane. The energy absorbed in PS II is enough to oxidize (split) water, releasing oxygen into the atmosphere; the electrons released from the oxidation of water replace the electrons that were boosted from the reaction center chlorophyll. As the electrons from the reaction center chlorophyll pass through the series of electron carrier proteins, hydrogen ions (H + ) are pumped across the membrane via chemiosmosis into the interior of the thylakoid. (If this sounds familiar, it should. We studied chemiosmosis in our exploration of cellular respiration in Cellular Respiration.) This action builds up a high concentration of H+ ions, and as they flow through ATP synthase, molecules of ATP are formed. These molecules of ATP will be used to provide free energy for the synthesis of carbohydrate in the Calvin cycle, the second stage of photosynthesis. The electron transport chain connects PS II and PS I. Similar to the events occurring in PS II, this second photosystem absorbs a second photon of light, resulting in the formation of a molecule of NADPH from NADP + . The energy carried in NADPH also is used to power the chemical reactions of the Calvin cycle.

Information presented and the examples highlighted in the section support concepts and learning objectives outlined in Big Idea 2 of the AP ® Biology Curriculum Framework, as shown in the table. The learning objectives listed in the Curriculum Framework provide a transparent foundation for the AP ® Biology course, an inquiry-based laboratory experience, instructional activities, and AP ® exam questions. A learning objective merges required content with one or more of the seven science practices.

Teacher Support

This section deals with the first half of photosynthesis. These reactions capture light energy and store it in chemicals for short periods of time to fuel the second half of photosynthesis. This is also where free oxygen can be released, but carbon dioxide is not captured or fixed.

The Science Practice Challenge Questions contain additional test questions for this section that will help you prepare for the AP exam. These questions address the following standards: [APLO 2.5][APLO 2.16][APLO 2.18][APLO 1.9][APLO 1.32][APLO 4.14][APLO 2.2][APLO 2.3][APLO 2.23][APLO 1.15][APLO 1.29]

How can light be used to make food? When a person turns on a lamp, electrical energy becomes light energy. Like all other forms of kinetic energy, light can travel, change form, and be harnessed to do work. In the case of photosynthesis, light energy is converted into chemical energy, which photoautotrophs use to build carbohydrate molecules ( Figure 8.9 ). However, autotrophs only use a few specific components of sunlight.

What Is Light Energy?

Everybody knows what a rainbow is, but some students may not be able to connect it to actual light sources. Obtain some way of refracting light, such as a prism, and use it to separate the components of several light sources, such as an older, incandescent light bulb, a new fluorescent type of light bulb and actual sunlight.

When discussing the electromagnetic spectrum, include the fact that when someone sets a radio station to its number, such as 92.1 or 1450 on the dial, they are really setting the radio to the specific wavelength of spectrum used by the station.

The sun emits an enormous amount of electromagnetic radiation (solar energy). Humans can see only a fraction of this energy, which portion is therefore referred to as “visible light.” The manner in which solar energy travels is described as waves. Scientists can determine the amount of energy of a wave by measuring its wavelength , the distance between consecutive points of a wave. A single wave is measured from two consecutive points, such as from crest to crest or from trough to trough ( Figure 8.10 ).

Visible light constitutes only one of many types of electromagnetic radiation emitted from the sun and other stars. Scientists differentiate the various types of radiant energy from the sun within the electromagnetic spectrum. The electromagnetic spectrum is the range of all possible frequencies of radiation ( Figure 8.11 ). The difference between wavelengths relates to the amount of energy carried by them.

Each type of electromagnetic radiation travels at a particular wavelength. The longer the wavelength (or the more stretched out it appears in the diagram), 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 a heavy 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 electromagnetic spectrum ( Figure 8.11 ) shows several types of electromagnetic radiation originating from the sun, including X-rays and ultraviolet (UV) rays. The higher-energy waves can penetrate tissues and damage cells and DNA, explaining why both X-rays and UV rays can be harmful to living organisms.

Absorption of Light

Stress the differences in the amount of energy at each wavelength, and the usefulness of the wavelengths for energy capture. Discuss what is in a “grow light” (artificial light source for plants grown indoors).

Light energy initiates the process of photosynthesis when pigments absorb the light. Organic pigments, whether in the human retina or the chloroplast thylakoid, have a narrow range of energy levels that they can absorb. Energy levels lower than those represented by red light are insufficient to raise an orbital electron to a populatable, excited (quantum) state. Energy levels higher than those in blue light will physically tear the molecules apart, called bleaching. So retinal pigments can only “see” (absorb) 700 nm to 400 nm light, which is therefore called visible light. For the same reasons, plants pigment molecules absorb only light in the wavelength range of 700 nm to 400 nm; plant physiologists refer to this range for plants as photosynthetically active radiation.

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 the colors to the human eye. The visible light portion of the electromagnetic spectrum shows the 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 ( Figure 8.12 ).

Understanding Pigments

Concentrate on the types and functions of chlorophylls and carotenoids that are found in leaves. Discuss how all of them are always there even though they are not visible in the summer. They are visible in the fall.

Ask the class what color coats people tend to wear in the summer and in the winter. Discuss why they do this.

Different kinds of pigments exist, and each absorbs only certain wavelengths (colors) of visible light. Pigments reflect or transmit the wavelengths they cannot absorb, making them appear in the corresponding color.

Chlorophylls and carotenoids are the two major classes of photosynthetic pigments found in plants and algae; each class has multiple types of pigment molecules. There are five major chlorophylls: a , b , c and d and a related molecule found in prokaryotes called bacteriochlorophyll. Chlorophyll a and chlorophyll b are found in higher plant chloroplasts and will be the focus of the following discussion.

With dozens of different forms, carotenoids are a much larger group of pigments. The carotenoids found in fruit—such as the red of tomato (lycopene), the yellow of corn seeds (zeaxanthin), or the orange of an orange peel (β-carotene)—are used as advertisements to attract seed dispersers. In photosynthesis, carotenoids function as photosynthetic pigments that are very efficient molecules for the disposal of excess energy. When a leaf is exposed to full sun, the light-dependent reactions are required to process an enormous amount of energy; if that energy is not handled properly, it can do significant damage. Therefore, many carotenoids reside in the thylakoid membrane, absorb excess energy, and safely dissipate that energy as heat.

Each type of pigment can be identified by the specific pattern of wavelengths it absorbs from visible light, which is the absorption spectrum . The graph in Figure 8.13 shows the absorption spectra for chlorophyll a , chlorophyll b , and a type of carotenoid pigment called β-carotene (which absorbs blue and green light). Notice how each pigment has a distinct set of peaks and troughs, revealing a highly specific pattern of absorption. Chlorophyll a absorbs wavelengths from either end of the visible spectrum (blue and red), but not green. Because green is reflected or transmitted, chlorophyll appears green. Carotenoids absorb in the short-wavelength blue region, and reflect the longer yellow, red, and orange wavelengths.

Many photosynthetic organisms have a mixture of pigments; using them, the organism can absorb energy from a wider range of wavelengths. Not all photosynthetic organisms have full access to sunlight. Some organisms grow underwater where light intensity and quality decrease and change with depth. 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 absorb most of the sunlight and scatter the remaining solar radiation ( Figure 8.14 ).

When studying a photosynthetic organism, scientists can determine the types of pigments present by generating absorption spectra. An instrument called a spectrophotometer can differentiate which wavelengths of light a substance can absorb. Spectrophotometers measure transmitted light and compute from it the absorption. By extracting pigments from leaves and placing these samples into a spectrophotometer, scientists can identify which wavelengths of light an organism can absorb. Additional methods for the identification of plant pigments include various types of chromatography that separate the pigments by their relative affinities to solid and mobile phases.

How Light-Dependent Reactions Work

Photosystems I and II can be confusing. Obtain diagrams of both systems and use them to go through the steps of the pathways. Discuss why some plants use the cyclic form of the systems and some the linear form. Discuss why oxygen is released during one pathway, but not the other.

The overall function of light-dependent reactions is to convert solar energy into chemical energy in the form of NADPH and ATP. This chemical energy supports the light-independent reactions and fuels the assembly of sugar molecules. The light-dependent reactions are depicted in Figure 8.15 . Protein complexes and pigment molecules work together to produce NADPH and ATP.

The actual step that converts light energy into chemical energy takes place in a multiprotein complex called a photosystem , two types of which are found embedded in the thylakoid membrane, photosystem II (PSII) and photosystem I (PSI) ( Figure 8.16 ). The two complexes differ on the basis of what they oxidize (that is, the source of the low-energy electron supply) and what they reduce (the place to which they deliver their energized electrons).

Both photosystems have the same basic structure; a number of antenna pigments to which the chlorophyll molecules are bound surround the reaction center where the photochemistry takes place. Each photosystem is serviced by the light-harvesting complex , which passes energy from sunlight to the reaction center; it consists of multiple antenna pigments that contain a mixture of 300–400 chlorophyll a and b molecules as well as other pigments like carotenoids. The absorption of a single photon or distinct quantity or “packet” of light by any of the chlorophylls pushes that molecule into an excited state. In short, the light energy has now been captured by biological molecules but is not stored in any useful form yet. The energy is transferred from chlorophyll to chlorophyll until eventually (after about a millionth of a second), it is delivered to the reaction center. Up to this point, only energy has been transferred between molecules, not electrons.

Visual Connection

• carbon dioxide

The reaction center contains a pair of chlorophyll a molecules with a special property. Those two chlorophylls can undergo oxidation upon excitation; they can actually give up an electron in a process called a photoact . It is at this step in the reaction center, this step in photosynthesis, that light energy is converted into an excited electron. All of the subsequent steps involve getting that electron onto the energy carrier NADPH for delivery to the Calvin cycle where the electron is deposited onto carbon for long-term storage in the form of a carbohydrate.PSII and PSI are two major components of the photosynthetic electron transport chain , which also includes the cytochrome complex . The cytochrome complex, an enzyme composed of two protein complexes, transfers the electrons from the carrier molecule plastoquinone (Pq) to the protein plastocyanin (Pc), thus enabling both the transfer of protons across the thylakoid membrane and the transfer of electrons from PSII to PSI.

The reaction center of PSII (called P680 ) delivers its high-energy electrons, one at the time, to the primary electron acceptor , and through the electron transport chain (Pq to cytochrome complex to plastocyanine) to PSI. P680’s missing electron is replaced by extracting a low-energy electron from water; thus, water is split and PSII is re-reduced after every photoact. Splitting one H 2 O molecule releases two electrons, two hydrogen atoms, and one atom of oxygen. Splitting two molecules is required to form one molecule of diatomic O 2 gas. About 10 percent of the oxygen is used by mitochondria in the leaf to support oxidative phosphorylation. The remainder escapes to the atmosphere where it is used by aerobic organisms to support respiration.

As electrons move through the proteins that reside between PSII and PSI, they lose energy. That energy is used to move hydrogen atoms from the stromal side of the membrane to the thylakoid lumen. Those hydrogen atoms, plus the ones produced by splitting water, accumulate in the thylakoid lumen and will be used to synthesize ATP in a later step. Because the electrons have lost energy prior to their arrival at PSI, they must be re-energized by PSI, hence, another photon is absorbed by the PSI antenna. That energy is relayed to the PSI reaction center (called P700 ). P700 is oxidized and sends a high-energy electron to NADP + to form NADPH. Thus, PSII captures the energy to create proton gradients to make ATP, and PSI captures the energy to reduce NADP + into NADPH. The two photosystems work in concert, in part, to guarantee that the production of NADPH will roughly equal the production of ATP. Other mechanisms exist to fine tune that ratio to exactly match the chloroplast’s constantly changing energy needs.

Generating an Energy Carrier: ATP

Discuss the similarities between ATP production in the light dependent reactions and in cellular respiration.

As in the intermembrane space of the mitochondria during cellular respiration, the buildup of hydrogen ions inside the thylakoid lumen creates a concentration gradient. The passive diffusion of hydrogen ions from high concentration (in the thylakoid lumen) to low concentration (in the stroma) is harnessed to create ATP, just as in the electron transport chain of cellular respiration. The ions build up energy because of diffusion and because they all have the same electrical charge, repelling each other.

To release this energy, hydrogen ions will rush through any opening, similar to water jetting through a hole in a dam. In the thylakoid, that opening is a passage through a specialized protein channel called the ATP synthase. The energy released by the hydrogen ion stream allows ATP synthase to attach a third phosphate group to ADP, which forms a molecule of ATP ( Figure 8.16 ). The flow of hydrogen ions through ATP synthase is called chemiosmosis because the ions move from an area of high to an area of low concentration through a semi-permeable structure.

Link to Learning

Visit this site and click through the animation to view the process of photosynthesis within a leaf.

• Electrons from PS I cause the reduction of NADPH to NADP + .
• Electrons from PSII cause the reduction of NADP + to NADPH.
• Electrons from PS I cause the reduction of NADP + to NADPH.
• Electrons are gained which causes the oxidation of NADP + .

Everyday Connection for AP® Courses

If the stomata were sealed, what would happen to oxygen ( O 2 ) and carbon dioxide ( CO 2 ) levels in a photosynthesizing leaf?

• O 2 levels would increase and CO 2 levels would decrease.
• CO 2 levels would increase and O 2 levels would decrease.
• O 2 and CO 2 levels would both decrease.
• O 2 and CO 2 levels would both increase.

Science Practice Connection for AP® Courses

Think about it.

On a hot, dry day, plants close their stomata to conserve water. Predict the impact of this on photosynthesis and justify your prediction.

The Think About It question is an application of Learning Objective 4.4 and Science Practice 6.4 because students are making a prediction about how interactions of cellular organelles and structures affect the rate of photosynthesis.

Possible answer:

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Scientists Discover ‘Dark Oxygen’ on the Ocean Floor Generated—Surprisingly—by Lumps of Metal

Researchers found that electric currents from polymetallic nodules are behind this alchemy—the same minerals that deep-sea miners are targeting

Twelve thousand feet under the ocean surface is a world of eternal midnight. No sunlight can penetrate to this depth to promote photosynthesis, so no plants are producing oxygen there. Yet, the life-supporting gas is abundant in this darkness-cloaked region, thanks to an unlikely oxygen factory: potato-sized, “battery rocks” on the seafloor.

New research published this week in the journal Nature Geoscience reveals that nature has devised a way to produce oxygen without the involvement of plants. It’s “an amazing and unexpected finding,” Daniel Jones , a researcher at the National Oceanography Center in the United Kingdom who wasn’t involved in the study, tells CNN ’s Katie Hunt.

Previously, scientists had understood oxygen to be the product of life itself, namely created by photosynthesizing autotrophs such as plants and algae. But the new study overturns that simplistic narrative. In fact, the discovery was so astonishing that, when lead author Andrew Sweetman first measured this “dark oxygen” in the Pacific Ocean’s Clarion-Clipperton Zone in 2013, he dismissed it outright.

“I just ignored it, because I’d been taught—you only get oxygen through photosynthesis,” Sweetman, an ecologist with the Scottish Association for Marine Science, tells Victoria Gill of BBC News . “Eventually, I realized that for years I’d been ignoring this potentially huge discovery.”

Tracing the origins of ‘dark oxygen’

Sweetman was part of a research team aiming to measure how much oxygen was being consumed by organisms at the bottom of the ocean. What he saw in the seawater scooped from the deep was a rise in oxygen levels, instead of the predicted decrease. Initially, he thought his sensors were faulty and sent them back to their manufacturer for recalibration—four to five times. 

In 2021, the opportunity came for Sweetman to return to the same spot, this time to survey the seabed for a deep-sea mining firm called the Metals Company. Using a different technique, Sweetman’s team once again measured dramatic increases in dissolved oxygen, writes Scientific American ’s Allison Parshall. He finally had good grounds to take the numbers seriously—and motivation to hunt for the oxygen’s real source.

First came a process of elimination. The scientists ruled out the possibility that microbes were behind the act: In lab tests simulating the seafloor, the researchers killed off any organisms in the water with mercury chloride. Yet the oxygen levels still rose.

That region of the CCZ was dotted with rock-like lumps known as polymetallic nodules, which form when metals such as manganese and cobalt precipitate out of the water and coalesce around shell fragments or shark teeth. Scientists zeroed in on these metals as the source of the oxygen, but they still weren’t sure how they created the gas. For instance, the oxygen wasn’t due to radioactive substances in the nodules splitting water molecules or the decomposition of oxygen-containing minerals like manganese oxide.

A breakthrough came when Sweetman was watching a documentary about deep-sea mining in a hotel bar in São Paulo, Brazil. According to CNN, he heard a character calling the nodules “a battery in a rock.” An idea zinged into his brain: Could the oxygen be generated electrochemically?

If you put a standard AA battery into saltwater, you’ll observe bubbles and hear a fizz—that’s the generation of hydrogen and oxygen gases as the electricity splits water molecules, a process known as electrolysis. The researchers suspected the same thing was happening in the deep ocean , thanks to the polymetallic nodules. Indeed, voltage measurements on the nodule surface confirmed the rocks carried as much juice as 0.95 volts. It was a little short of the theoretical requisite of 1.5 volts for seawater electrolysis, but the researchers suspected that the nodules clustering together helped the reaction overcome this hurdle.

This “is one of the most fascinating things [I and my lab] have ever worked on,” Franz Geiger , a physical chemist at Northwestern University and co-author of the paper, tells Scientific American .

The naturally occurring rock-batteries force scientists to broaden the theories of life’s evolutionary trajectory. Scientists had assumed that complex life evolved after photosynthesizing cyanobacteria cooked up enough oxygen on early Earth . Perhaps life could have leveled up in pockets, feeding off oxygen in unlikely places.

“I think we therefore need to revisit questions like: Where could aerobic life have begun?” Sweetman tells Live Science ’s Sascha Pare. The same process could also be playing out in other ocean worlds, such as Enceladus and Europa.

Targets for deep-sea mining

Whether they had a hand in shaping life’s evolution or not, the nodules are important to marine life today. A 2013 survey of the CCZ found that half of the documented megafauna species—those large enough for the naked eye to make out—were present only on the nodules. The deep sea remains a poorly studied region for biodiversity, with up to two thirds of its dwellers still unknown to science.

However, the CCZ is already attracting interest for its deep-sea mining potential. The very nodules that perform this oxygen-generating alchemy are also a mining target for their richness in rare earth metals . These elements, which include cobalt, nickel, copper and manganese, are important constituents in batteries, smartphones, wind turbines and solar panels.

Deep-sea mining , which is still in an experimental phase rather than a full-scale industry, has garnered immense backlash. So far, 27 countries and 52 corporations have pledged support for a moratorium on deep sea mining. More than 800 scientists and policy experts have petitioned against the practice. Mining activities in international waters, such as the CCZ, are regulated by the International Seabed Authority, which issues permits for mining exploration.

The Metals Company, the same firm that sponsored the new study, was the first to receive authorization for a mining trial in 2022, to the surprise and dismay of conservationists. To date, 16 deep-sea mining contracts have been awarded to private companies to survey approximately 400,000 square miles of the seafloor in the CCZ.

Studies like Sweetman’s are important to uncover the full scale of what’s at stake. “I don’t see this study as something that will put an end to mining,” he tells BBC News. But what researchers can do, he adds, is gather the data that can help stakeholders make informed decisions, and possibly spark new ideas about how to minimize the fallout, if—or when—the industry ever gets off the ground.

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Shi En Kim | | READ MORE

Shi En Kim is a Washington, D.C.-based freelance science journalist. Her work has appeared in  National Geographic ,  Scientific American , the  Atlantic ,  Popular Science  and others. In 2021, she interned at  Smithsonian  magazine as an AAAS Mass Media Fellow.

Tundra Vegetation to Grow Taller, Greener Through 2100, NASA Study Finds

• August 6, 2024

Source: Erica McNamee, NASA Goddard Space Flight Center

Warming global climate is changing the vegetation structure of forests in the far north. It’s a trend that will continue at least through the end of this century, according to NASA researchers. The change in forest structure could absorb more of the greenhouse gas carbon dioxide (CO 2 ) from the atmosphere, or increase permafrost thawing, resulting in the release of ancient carbon. Millions of data points from the Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) and Landsat missions helped inform this latest research, which will be used to refine climate forecasting computer models.

Tundra landscapes are getting taller and greener. With the warming climate, the vegetation of forests in the far north is changing as more trees and shrubs appear. These shifts in the vegetation structure of boreal forests and tundra will continue for at least the next 80 years, according to NASA scientists in a recently published study. Boreal forests generally grow between 50 and 60 degrees north latitude, covering large parts of Alaska, Canada, Scandinavia, and Russia. The biome is home to evergreens such as pine, spruce, and fir. Farther north, the permafrost and short growing season of the tundra biome have historically made it hard to support large trees or dense forests. The vegetation in those regions has instead been made up of shrubs, mosses, and grasses. The boundary between the two biomes is difficult to discern. Previous studies have found high-latitude plant growth increasing and moving northward into areas that earlier were sparsely covered in the shrubs and grasses of the tundra. Now, the new NASA-led study finds an increased presence of trees and shrubs in those tundra regions and adjacent transitional forests, where boreal regions and tundra meet. This is predicted to continue until at least the end of the century.

“The results from this study advance a growing body of work that recognizes a shift in vegetation patterns within the boreal forest biome,” said Paul Montesano, lead author for the paper and research scientist at NASA Goddard’s Space Flight Center in Greenbelt, Maryland. “We’ve used satellite data to track the increased vegetation growth in this biome since 1984, and we found that it’s similar to what computer models predict for the decades to come. This paints a picture of continued change for the next 80 or so years that is particularly strong in transitional forests.” Scientists found predictions of “positive median height changes” in all tundra landscapes and transitional – between boreal and tundra – forests featured in this study. This suggests trees and shrubs will be both larger and more abundant in areas where they are currently sparse. “The increase of vegetation that corresponds with the shift can potentially offset some of the impact of rising CO 2 emissions by absorbing more CO 2 through photosynthesis,” said study co-author Chris Neigh, NASA’s Landsat 8 and 9 project scientist at Goddard. Carbon absorbed through this process would then be stored in the trees, shrubs, and soil. The change in forest structure may also cause permafrost areas to thaw as more sunlight is absorbed by the darker colored vegetation. This could release CO 2 and methane that has been stored in the soil for thousands of years. In their paper published in Nature Communications Earth & Environment in May, NASA scientists described the mixture of satellite data, machine learning, climate variables, and climate models they used to model and predict how the forest structure will look for years to come. Specifically, they analyzed nearly 20 million data points from NASA’s ICESat-2. They then matched these data points with tens of thousands of scenes of North American boreal forests between 1984 to 2020 from Landsat, a joint mission of NASA and the U.S. Geological Survey. Advanced computing capabilities are required to create models with such large quantities of data, which are called “big data” projects.

The ICESat-2 mission uses a laser instrument called lidar to measure the height of Earth’s surface features (like ice sheets or trees) from the vantage point of space. In the study, the authors examined these measurements of vegetation height in the far north to understand what the current boreal forest structure looks like. Scientists then modeled several future climate scenarios — adjusting to different scenarios for temperature and precipitation — to show what forest structure may look like in response. “Our climate is changing and, as it changes, it affects almost everything in nature,” said Melanie Frost, remote sensing scientist at NASA Goddard. “It’s important for scientists to understand how things are changing and use that knowledge to inform our climate models.”

• Categories: Benefits to People , Carbon and Climate , Feature-FrontPage , Forest Management , News

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AP®︎/College Biology

Course: ap®︎/college biology   >   unit 3.

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

The light-dependent reactions

• The Calvin cycle
• Photosynthesis evolution
• Photosynthesis review

Introduction

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

Overview of the light-dependent reactions

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

What is a photosystem?

Photosystem i vs. photosystem ii.

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

Photosystem II

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

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

Additional references:

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