what is the end result in photosynthesis

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Photosynthesis

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Photosynthesis Definition

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

Photosynthesis Equation

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

Stages of Photosynthesis

The light reactions.

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

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

The Calvin Cycle

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

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

Products of Photosynthesis

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

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

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Development of the idea

Overall reaction of photosynthesis.

• Basic products of photosynthesis
• Evolution of the process
• Light intensity and temperature
• Carbon dioxide
• Internal factors
• Energy efficiency of photosynthesis
• Structural features
• Light absorption and energy transfer
• The pathway of electrons
• Evidence of two light reactions
• Photosystems I and II
• Quantum requirements
• The process of photosynthesis: the conversion of light energy to ATP
• Elucidation of the carbon pathway
• Carboxylation
• Isomerization/condensation/dismutation
• Phosphorylation
• Regulation of the cycle
• Products of carbon reduction
• Photorespiration
• Carbon fixation in C 4 plants
• Carbon fixation via crassulacean acid metabolism (CAM)
• Differences in carbon fixation pathways
• The molecular biology of photosynthesis

Why is photosynthesis important?

What is the basic formula for photosynthesis, which organisms can photosynthesize.

photosynthesis

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• Table Of Contents

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

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

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

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

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

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

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

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

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

General characteristics

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

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

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

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

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

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Photosynthetic Cells

Cells get nutrients from their environment, but where do those nutrients come from? Virtually all organic material on Earth has been produced by cells that convert energy from the Sun into energy-containing macromolecules. This process, called photosynthesis, is essential to the global carbon cycle and organisms that conduct photosynthesis represent the lowest level in most food chains (Figure 1).

What Is Photosynthesis? Why Is it Important?

Most living things depend on photosynthetic cells to manufacture the complex organic molecules they require as a source of energy. Photosynthetic cells are quite diverse and include cells found in green plants, phytoplankton, and cyanobacteria. During the process of photosynthesis, cells use carbon dioxide and energy from the Sun to make sugar molecules and oxygen. These sugar molecules are the basis for more complex molecules made by the photosynthetic cell, such as glucose. Then, via respiration processes, cells use oxygen and glucose to synthesize energy-rich carrier molecules, such as ATP, and carbon dioxide is produced as a waste product. Therefore, the synthesis of glucose and its breakdown by cells are opposing processes.

However, photosynthesis doesn't just drive the carbon cycle — it also creates the oxygen necessary for respiring organisms. Interestingly, although green plants contribute much of the oxygen in the air we breathe, phytoplankton and cyanobacteria in the world's oceans are thought to produce between one-third and one-half of atmospheric oxygen on Earth.

What Cells and Organelles Are Involved in Photosynthesis?

Chlorophyll A is the major pigment used in photosynthesis, but there are several types of chlorophyll and numerous other pigments that respond to light, including red, brown, and blue pigments. These other pigments may help channel light energy to chlorophyll A or protect the cell from photo-damage. For example, the photosynthetic protists called dinoflagellates, which are responsible for the "red tides" that often prompt warnings against eating shellfish, contain a variety of light-sensitive pigments, including both chlorophyll and the red pigments responsible for their dramatic coloration.

What Are the Steps of Photosynthesis?

Photosynthesis consists of both light-dependent reactions and light-independent reactions . In plants, the so-called "light" reactions occur within the chloroplast thylakoids, where the aforementioned chlorophyll pigments reside. When light energy reaches the pigment molecules, it energizes the electrons within them, and these electrons are shunted to an electron transport chain in the thylakoid membrane. Every step in the electron transport chain then brings each electron to a lower energy state and harnesses its energy by producing ATP and NADPH. Meanwhile, each chlorophyll molecule replaces its lost electron with an electron from water; this process essentially splits water molecules to produce oxygen (Figure 5).

Once the light reactions have occurred, the light-independent or "dark" reactions take place in the chloroplast stroma. During this process, also known as carbon fixation, energy from the ATP and NADPH molecules generated by the light reactions drives a chemical pathway that uses the carbon in carbon dioxide (from the atmosphere) to build a three-carbon sugar called glyceraldehyde-3-phosphate (G3P). Cells then use G3P to build a wide variety of other sugars (such as glucose) and organic molecules. Many of these interconversions occur outside the chloroplast, following the transport of G3P from the stroma. The products of these reactions are then transported to other parts of the cell, including the mitochondria, where they are broken down to make more energy carrier molecules to satisfy the metabolic demands of the cell. In plants, some sugar molecules are stored as sucrose or starch.

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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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ENCYCLOPEDIC ENTRY

Photosynthesis.

Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.

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Learning materials, instructional links.

• Photosynthesis (Google doc)

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

The process

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

Chlorophyll

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

Light-dependent Reactions vs. Light-independent Reactions

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

C3 and C4 Photosynthesis

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

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What Is Produced As a Result of Photosynthesis?

10 Facts on Photosynthesis

All living things consume energy in order to survive. Animals get their energy from the food they eat, but plants must absorb energy in a different way. Though plants use their roots to pull water and some nutrients from soil, the majority of plants' energy comes from the sun. Plants are able to convert sunlight into usable energy, in the form of glucose, due to the structure of their cells and a process called photosynthesis.

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

Plants get most of the energy they need to survive via a two-stage process called photosynthesis. In the first stage, called the light-dependent reaction, sunlight is converted into two molecules. In the second stage, called the light-independent reaction, these molecules work together to form and synthesize glucose. Glucose is a sugar that plants use for energy.

How Photosynthesis Works

The cells of plants and animals differ slightly, in structure. For example, certain plant cells contain organelles called plastids, which help the cells store energy. Chloroplasts are plastids that contain the green pigment chlorophyll. This pigment is responsible for absorbing sunlight during the process of photosynthesis.

Photosynthesis is a two-stage process. The first stage of photosynthesis is called the light-dependent reaction because sunlight must be present in order for the reaction to occur. During this stage, chloroplasts absorb and trap sunlight, converting it into chemical energy. Specifically, the light is converted into two molecules to be used during the second stage of photosynthesis. These two molecules are nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP).

The second stage of photosynthesis is called the light-independent reaction because sunlight is not necessary for it to occur. In this stage, the two molecules formed during the light-dependent reaction work together to produce glucose. Hydrogen atoms from NADPH help to form the glucose, while ATP provides the energy necessary to synthesize it.

The Importance of Glucose

Glucose is a sugar that many plants, animals and fungi use for energy. In plants, glucose is produced as a result of photosynthesis. Plants need the energy glucose provides in order to grow and reproduce. Glucose is also required for the process of cellular respiration, in which plants convert carbon dioxide from the air into oxygen.

Because plants rely on sunlight to make glucose, inadequate sunlight can be a problem for plants that live in shady or cloudy areas. To deal with this problem, most plants store glucose inside their bodies to use when sunlight is scarce. Plants usually store glucose as starch. Starch granules can be found inside plant cells, in organelles called amyloplasts.

Without glucose, plants would not have the energy necessary to grow, reproduce or carry out cellular respiration. This means that without glucose, plant life could not exist on Earth.

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• University of Illinois: Photosynthesis
• UCSB ScienceLine: How Are Respiration and Photosynthesis Related?

About the Author

Maria Cook is a freelance and fiction writer from Indianapolis, Indiana. She holds an MFA in Creative Writing from Butler University in Indianapolis. She has written about science as it relates to eco-friendly practices, conservation and the environment for Green Matters.

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5.1 Overview of Photosynthesis

Learning objectives.

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

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

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

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

Link to Learning

Click the following link to learn more about photosynthesis.

Solar Dependence and Food Production

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

Heterotrophs are organisms incapable of photosynthesis that must therefore obtain energy and carbon from food by consuming other organisms. The Greek roots of the word heterotroph mean “other” ( hetero ) “feeder” ( troph ), meaning that their food comes from other organisms. Even if the food organism is another animal, this food traces its origins back to autotrophs and the process of photosynthesis. Humans are heterotrophs, as are all animals. Heterotrophs depend on autotrophs, either directly or indirectly. Deer and wolves are heterotrophs. A deer obtains energy by eating plants. A wolf eating a deer obtains energy that originally came from the plants eaten by that deer. The energy in the plant came from photosynthesis, and therefore it is the only autotroph in this example ( Figure 5.3 ). Using this reasoning, all food eaten by humans also links back to autotrophs that carry out photosynthesis.

Everyday Connection

Photosynthesis at the grocery store.

Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle contains hundreds, if not thousands, of different products for customers to buy and consume ( Figure 5.4 ).

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

Main Structures and Summary of Photosynthesis

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

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

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

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

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

Visual Connection

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

The Two Parts of Photosynthesis

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

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What Are the Products of Photosynthesis?

Result of Photosynthesis in Plants

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Photosynthesis is the name given to the set of chemical reactions performed by plants to convert energy from the sun into chemical energy in the form of sugar. Specifically, plants use energy from sunlight to react carbon dioxide and water to produce sugar ( glucose ) and oxygen . Many reactions occur, but the overall chemical reaction for photosynthesis is:

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

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

Key Takeaways

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

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

Intermediate Products of Photosynthesis

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

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

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

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

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

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

Factors That Affect the Rate of Photosynthesis

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

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

What Is Not a Product of Photosynthesis?

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

• Bidlack, J.E.; Stern, K.R.; Jansky, S. (2003). Introductory Plant Biology . New York: McGraw-Hill. ISBN 978-0-07-290941-8.
• Blankenship, R.E. (2014). Molecular Mechanisms of Photosynthesis (2nd ed.). John Wiley & Sons. ISBN 978-1-4051-8975-0.
• Reece J.B., et al. (2013). Campbell Biology . Benjamin Cummings. ISBN 978-0-321-77565-8.
• Examples of Chemical Reactions in Everyday Life
• A to Z Chemistry Dictionary
• Phases of the Bacterial Growth Curve
• Photosynthesis Basics - Study Guide
• Photosynthesis Vocabulary Terms and Definitions
• The Photosynthesis Formula: Turning Sunlight into Energy
• Calvin Cycle Steps and Diagram
• 10 Fascinating Photosynthesis Facts
• Chloroplast Function in Photosynthesis
• Chlorophyll Definition and Role in Photosynthesis
• What Is the Primary Function of the Calvin Cycle?
• The Balanced Chemical Equation for Photosynthesis
• All About Photosynthetic Organisms
• Thylakoid Definition and Function
• Simple Chemical Reactions
• An Introduction to Types of Respiration

What is photosynthesis?

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

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

How does photosynthesis start?

• Location of photosynthesis

Light-dependent reactions

• The Calvin cycle

Types of photosynthesis

Additional resources.

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

Types of photosynthetic processes

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

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

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

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

The Photosynthesis equation

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

The oxygenic photosynthesis equation is: 

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

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

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

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

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

How is carbon dioxide and oxygen exchanged?

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

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

How do plants absorb sunlight for photosynthesis?

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

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

Related: What if humans had photosynthetic skin?

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

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

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

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

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

Where in the plant does photosynthesis take place?

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

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

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

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

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

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

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

Light-independent reactions: The Calvin cycle

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

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

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

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

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

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

C3 photosynthesis

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

C4 photosynthesis

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

CAM photosynthesis

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

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

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

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Photosynthesis

Part of Science Biology

What is photosynthesis?

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Animals need to eat food to get their energy. All animals, including humans, eat food that was, or is, a plant or an animal.

But green plants and algae can use light energy to make their own food! This process called photosynthesis .

Almost all life on Earth depends upon this process.

Why is photosynthesis so important?

Photosynthesis is really important for animals, including humans because

• without photosynthesis we wouldn’t have food because it converts energy from the sun into chemical energy for the food chains.
• photosynthesis keeps the levels of oxygen and carbon dioxide in the atmosphere in balance – without it we would very quickly run out of oxygen.

Photosynthesis is really important for the plant because it provides the plant with food:

• some of the glucose is used immediately, to give the plant energy in the process of respiration.
• some of the glucose is changed into starch and stored in all parts of the plant. When it is needed, it is converted back into glucose.

Adaptations of the leaf

In most plants photosynthesis happens in the leaves. Leaves have adapted so that photosynthesis takes place efficiently. The table describes some of its adaptations:

A leaf usually has a large surface area, so that it can absorb a lot of light. It's top surface is protected from water loss, disease and weather damage by a waxy cuticle, which does not stop light entering the leaf.

The upper part of the leaf is where the light falls, and it contains many cells called palisade cells. This has many chloroplasts, with lots of chlorophyll to trap as much light as possible. It is shaped like a tall box which helps pack them closely together.

Carbon dioxide

Plants get the carbon dioxide they need from the air through their leaves. It moves by diffusion through small holes in the underside of the leaf called stomata. Guard cells control the size of the stomata so that the leaf does not lose too much water in hot, windy or dry conditions.

The lower part of the leaf is a spongy layer with loose-fitting cells. Between the cells in this layer there are 'air spaces' - a bit like a sponge. These allow the gases to diffuse through the leaf.Stomata let carbon dioxide enter the leaf, and let the oxygen produced in photosynthesis leave the leaf easily. In many plants, stomata are open during the day and closed at night.

The water needed for photosynthesis is absorbed through the roots and transported through tubes to the leaf.The roots have a type of cell called a root hair cell. These project out from the root into the soil, and have a big surface area and thin walls. This lets water pass into them easily.Note that root cells do not contain chloroplasts, as they are normally in the dark and cannot carry out photosynthesis.

Results Only the areas of the leaf that were originally green tested positive for starch. The discoloured areas tested negative. As the green areas contained chlorophyll and the white did not, this proves that chlorophyll is needed for photosynthesis.

Investigating the production of oxygen

Food Chains

• count 1 of 11

Gas Exchange and Respiration

• count 2 of 11

• count 3 of 11

Photosynthesis powers our world, but what fuels this fundamental process?

Palo Alto, CA— It’s hard to overstate the importance of photosynthesis , the biochemical pathway by which plants, algae, and certain bacteria convert the Sun’s energy into the organic material that feeds the entire living biosphere. But there are still aspects of the photosynthetic function that scientists are working to understand. Expanding their knowledge could help improve agriculture and fight climate change.

Photosynthesis provides the foundation for life on Earth by making our atmosphere oxygen rich; it also sequesters carbon pollution from human activity and forms the basis of the food chain.

“On a molecular level, photosynthesis has two components,” explained Carnegie Science algae expert Adrien Burlacot. “There’s the sunlight-powered splitting of water molecules, which produces the energy molecules that are used by all cells, and the fixation of carbon dioxide from the atmosphere into organic material, or biomass, which consumes chemical energy.”

He added: “But there’s a disconnect that has caused decades of debate. This is because the chemical energy needed to power the second half of this process—the transformation of carbon dioxide into biomass—is different than the energy currency created by splitting water molecules. And the processes involved in converting the basic energy molecules into the energy used to synthesize sugars are still mysterious.”

When it comes to photosynthetic efficiency, organisms have wide variation in their capacity to transform sunlight into biomass. While a tree or a grass would typically be able to use between 0.5 and 1 percent of the sun’s energy, microalgae are able to use up to 5 percent of that energy.

“Photosynthesis in plants is very inefficient,” Burlacot added. “Because algae are much better at it, they hold important potential for understanding how to improve this fundamental process that underpins nearly every aspect of life on our planet.”

Part of the secret lies in algae harboring a special biochemical system for concentrating carbon dioxide within the photosynthetic apparatus. For the last couple of years, Burlacot’s lab has been investigating how algae power this carbon-concentrating ability by studying Chlamydomonas , a group of photosynthetic algae that are found around the globe in fresh and saltwater, moist soils, and even at the surface of snow. Recently, they expanded this to examine how the basic energy currency is converted to the chemical energy necessary for the carbon-fixation process itself in algae.

In a paper published in The Plant Cell , Burlacot’s team revealed that three biochemical energy circuits power carbon fixation in Chlamydomonas . Their work demonstrated that all three pathways can sustain high rates of sugar production. However, the three circuits were not all equally efficient.

“Two out of three pathways are wasting twice more energy than the most efficient one,” Burlacot said. “And—interestingly—the two most efficient pathways are not present in crop plants.”

Looking ahead, the group wants to elucidate the contributions of each of the three mechanisms and to build connections between these and similar pathways in other photosynthetic organisms. A big question remains on whether difference in photosynthetic efficiency between species could be related to the energy circuits that they are using.

“We are attempting to understand biochemical and biophysical steps of how algae capture carbon dioxide, which could enable us to improve the efficiency of important crop plants and to enhance carbon capture solutions,” Burlacot concluded. “More work is needed, and we are revealing the full story of how carbon fixation is fueled.”

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Will Cori Bush be ousted like Bowman? New poll shows her opponent leading by one point

WASHINGTON — Rep. Cori Bush, D-Mo., may be in trouble after a new poll found her opponent in the Democratic primary for Missouri's 1st Congressional District leading her by one point.

The poll, conducted by The Mellman Group between June 18 and June 22, found that St. Louis County Prosecuting Attorney Wesley Bell overcame a double-digit deficit in January to lead Bush 43% to 42%. Four percent of the survey respondents supported other candidates on the ballot while 11% were undecided. He has picked up support across various groups, the poll found, including among whites and Blacks, men and women and those under and over the age of 50. 

Bell also leads Bush in job performance and favorability ratings. Sixty-one percent of survey respondents gave Bell a positive rating on his job performance while only 49% gave Bush a positive rating. 60% of respondents are favorable towards Bush while 64% are favorable towards Bell. 

The poll, conducted among 400 voters in Missouri’s 1st Congressional District, has a margin of error of plus or minus 4.9 percentage points. Politico first obtained the poll. 

Bush is a member of “The Squad” made up of progressive congressional Democrats. The latest poll comes as Rep. Jamaal Bowman, D-N.Y., lost the Democratic primary for New York's 16 th  Congressional District to opponent George Latimer Tuesday, marking the first ouster of a member of the "Squad."

How will Karen Read’s trial end? Here’s what legal experts had to say.

As jury deliberations begin in karen read’s murder trial, several legal experts offered their takeaways and predictions in the sensational case..

By Abby Patkin

It’s a key question in the case that has launched a thousand theories: Will Karen Read walk free, or will she end up behind bars? 

It’s all up to jurors now. 

Deliberations began Tuesday after the prosecution and defense offered up their closing arguments . And following more than eight weeks of witness testimony, jurors are left with heated voicemails , crude texts , a broken taillight, and two vastly different theories of what happened to Boston Police Officer John O’Keefe. 

On the one hand, there’s the state’s argument that Read drunkenly and intentionally backed her SUV into O’Keefe — her boyfriend of two years — one snowy morning in Canton. Prosecutors allege the couple’s deteriorating relationship and Read’s jealousy drove her to kill as she dropped O’Keefe off at a house party sometime after midnight on Jan. 29, 2022.

More on Karen Read:

Jury deliberations are coming up in Karen Read’s murder trial. These are the possible outcomes.

A ‘tall blue wall’ or a ‘three-card monte’ trick karen read’s case in jury’s hands after closing arguments., watch: closing arguments in karen read’s murder trial.

Read’s lawyers have another theory: That O’Keefe walked into 34 Fairview Road that morning and was viciously beaten, attacked by the homeowners’ dog, and left to die in a blizzard. They say Read was framed in a conspiracy meant to protect a well-connected local family, and that law enforcement officials were in on the coverup.

Though the jury’s verdict remains undecided, several legal experts who spoke with Boston.com ahead of closing arguments agreed: For better or for worse, Read’s trial has left a lasting impression. 

“The entire case is unusual from my perspective — John O’Keefe is not the typical victim and Karen Read is not the typical defendant,” attorney Katherine Loftus said in an email interview. She pointed specifically to Read’s unprecedented media campaign and accusations of a coverup and “lazy police work.” 

“It is truly a story that would not be believed if it was written as fiction,” Loftus added. “I expect that this trial will cause divisions and arguments amongst friends and families for many years to come.”

Legal experts’ takeaways on the trial

Daniel Medwed , a criminal law professor at Northeastern University, noted the growing public fascination in Read’s case. 

“It seems to have morphed from largely a local story to one with national reverberations,” he said in an email interview. “I think the unique ingredients of the case — the death of a police officer, claims of a vast law enforcement cover-up, the prospect of a woman on trial, and the ample forensic and technological evidence — has created an enticing stew that almost everyone wants to consume.”

Read’s lawyers, he added, were impressive in their effective cross-examination of prosecution witnesses. Loftus likewise praised the defense for their “excellent job of attacking each witness and each piece of evidence.” She pointed to an old law school adage, “a brick is not a wall,” and said prosecutors have an uphill battle to keep their proverbial “wall” from crumbling.

One notable example of this came during the testimony of the lead Massachusetts State Police investigator, Trooper Michael Proctor, who admitted he “dehumanized” Read in vulgar texts sent to friends, family, and colleagues.

Rosanna Cavallaro , a professor of criminal law and evidence at Suffolk University Law School, said those texts — where Proctor called Read a “wack job c**t” and made light of her Crohn’s disease — “really significantly compromised” his testimony.

While prosecutors attempted to cushion the blow by introducing Proctor’s texts before the defense could, “the nature of the comments was so stark and I think surprising to the average juror that an investigator at a murder scene or a possible murder scene would be behaving in that way, or making comments that had that tone to them,” Cavallaro noted. 

What evidence will matter most to jurors?

Cavallaro said she was also struck by the dispute over the timestamp for witness Jennifer McCabe’s “hos long to die in cold” Google search.

McCabe told jurors she made the search at Read’s insistence shortly after the women found O’Keefe’s body around 6 a.m. on Jan. 29, 2022. Two digital forensics experts, Jessica Hyde and Ian Whiffin, testified that McCabe’s phone data puts the “hos long” search at 6:24 a.m.

But a defense expert, Richard Green, testified that McCabe made the search “at or before” 2:27 a.m. that day. Hyde and Whiffin both said the earlier timestamp actually indicates when McCabe first opened the browser tab.

“The average juror doesn’t have any insight of their own,” Cavallaro said. “The whole basis for expert testimony is that it’s a subject matter that’s beyond the average juror. That the average juror has to say, ‘OK, which of these experts seems to me to know what they’re doing?’”

Medwed, meanwhile, speculated the crash data and geolocation evidence might weigh heavily on jury deliberations, “both in terms of the defendant’s location at precise times and the ability of the technology to place Officer O’Keefe in specific locations.”

And Martin G. Weinberg , a prominent Boston-based criminal defense attorney, pointed back to Proctor’s texts.

“Jurors mirror the public,” he noted in an email interview. Some, he said, will be so offended by the messages “that they will find it very hard to trust that the remainder of the case was insulated from the bias and disrespect shown by the State Police lead investigator.”

Weinberg drew similarities to the O.J. Simpson murder trial, where jurors balked at Los Angeles Police Det. Mark Fuhrman’s “highly offensive racial bias.” 

“Other jurors will instead predictably focus on the multiple forensic experts that ADA [Adam] Lally pivoted his case around with apparent skill and precision,” Weinberg predicted. “How each side presents its arguments, first the lawyers in court and then the jurors in the sacred secrecy of jury deliberations, will determine the outcome.”

How will Karen Read’s trial end? 

Either way, Weinberg noted, “I doubt a fast verdict.”

According to Loftus, the length of the trial plays into the decision-making process.

“In addition to that, the case has become a lightning rod in the greater community, and it is hard to imagine that the same is not happening in the jury room,” Loftus said. “I anticipate we will know rather quickly whether they are struggling to come to a unanimous verdict — either they return swiftly, or alternatively, if the verdict takes longer, it often is an indication that the jurors cannot agree.”

The upcoming Fourth of July holiday may also mean jurors are antsy to reach a decision sooner than later, she noted. 

Still, the jury’s ultimate decision is anyone’s guess. 

Medwed, who weighed in before the defense rested its case, said one possibility is a split or “compromise” verdict where Read is convicted on some charges but acquitted on others. Read has pleaded not guilty to charges of second-degree murder, motor vehicle manslaughter while driving under the influence, and leaving the scene of a collision causing injury and death.

“I would be mildly surprised if she’s convicted on all charges given the holes in the case, but I may be wrong,” Medwed added. 

There’s no possibility that Read will be convicted of second-degree murder at this point, Loftus opined. While she acknowledged there’s a “small chance” Read could be found guilty of the manslaughter charge, she said this outcome is also unlikely. 

Given the circumstances, Cavallaro said it seems doubtful all 12 jurors will think the prosecution’s case is airtight.

“There’s been a bit of a side show with people outside of the criminal process taking a kind of extraordinary interest in it and drumming up controversy,” she said of Read’s case. “But at the end of the day, I think there’s a group of 12 people in there that are paying careful attention and that are going to be able to figure out whether or not … the state has met the very high burden that they’re required to meet.” 

Read’s next steps will depend on the verdict she receives. She could file an appeal in the event of a conviction, and Loftus noted that the defense team’s allegations of police misconduct may be key.

“Given that there have been no substantiated findings as of yet against any of the involved police witnesses, it would likely be an uphill battle,” she acknowledged. 

However, if any charges or findings result from the State Police internal affairs investigation into Proctor or the federal probe of the case, “it likely sparks at least an inquiry into the basis for an appeal at a later date,” Loftus said. 

A trickier question is whether prosecutors would retry Read’s case if a hung jury results in a mistrial. While Loftus suggested prosecutors would “most certainly take the ‘second bite at the apple,’” Medwed was more doubtful. 

“Retrials are notoriously difficult even in a run of the mill case because the passage of time makes the evidence less fresh and memories less reliable,” he said. “And this case is far from run of the mill. If new evidence emerges, though, that could change things.”

Regardless of the trial’s outcome, Weinberg said the “skilled lawyering” from Read’s attorneys “has hopefully had a positive effect even beyond this single trial.”

He pointed to law enforcement officers’ “solemn obligation” to follow best police practices and avoid stigmatizing a defendant, adding, “The burden of being accused as Ms. Read has of a profoundly serious offense requires no less.”

Loftus, meanwhile, described the trial as a “fascinating” window into the division pervasive in the U.S. today. 

“Similar to the desire to pick a ‘team’ in our current political environment, so is the desire to fight for Karen Read’s guilt or innocence, seemingly with no ability to waiver in between,” she said. “I expect that the fervor will eventually dissipate, but it is going to take some time before it completely subsides (if ever).”

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8.3: The Light-Dependent Reactions of Photosynthesis

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Learning Objectives

• Explain how plants absorb energy from sunlight
• Describe short and long wavelengths of light
• Describe how and where photosynthesis takes place within a plant

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 \(\PageIndex{1}\)). However, autotrophs only use a few specific components of sunlight.

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 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 \(\PageIndex{2}\)).

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 \(\PageIndex{3}\)). 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 \(\PageIndex{3}\)) 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

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 \(\PageIndex{4}\)).

Understanding Pigments

Different kinds of pigments exist, and each has evolved to absorb 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 \(\PageIndex{5}\) 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 \(\PageIndex{6}\)).

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

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 \(\PageIndex{7}\). 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 \(\PageIndex{7}\)). 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 proteins 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 proteins 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.

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 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

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 \(\PageIndex{8}\)). 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.

Interactive Link

View this video showing the process of photosynthesis within a leaf.

The pigments of the first part of photosynthesis, the light-dependent reactions, absorb energy from sunlight. A photon strikes the antenna pigments of photosystem II to initiate photosynthesis. The energy travels to the reaction center that contains chlorophyll a to the electron transport chain, which pumps hydrogen ions into the thylakoid interior. This action builds up a high concentration of ions. The ions flow through ATP synthase via chemiosmosis to form molecules of ATP, which are used for the formation of sugar molecules in the second stage of photosynthesis. Photosystem I absorbs a second photon, which results in the formation of an NADPH molecule, another energy and reducing power carrier for the light-independent reactions.

Review Questions

Which of the following structures is not a component of a photosystem?

• ATP synthase
• antenna molecule
• reaction center
• primary electron acceptor

How many photons does it take to fully reduce one molecule of NADP + to NADPH?

Which complex is not involved in the establishment of conditions for ATP synthesis?

• photosystem I
• photosystem II
• cytochrome complex

From which component of the light-dependent reactions does NADPH form most directly?

Free Response

Describe the pathway of electron transfer from photosystem II to photosystem I in light-dependent reactions.

Answer: A photon of light hits an antenna molecule in photosystem II, and the energy released by it travels through other antenna molecules to the reaction center. The energy causes an electron to leave a molecule of chlorophyll a to a primary electron acceptor protein. The electron travels through the electron transport chain and is accepted by a pigment molecule in photosystem I.

What are the roles of ATP and NADPH in photosynthesis?

Answer: Both of these molecules carry energy; in the case of NADPH, it has reducing power that is used to fuel the process of making carbohydrate molecules in light-independent reactions.

Art Connections

Figure \(\PageIndex{8}\): What is the source of electrons for the chloroplast electron transport chain?

• Carbon dioxide

Contributors and Attributions

Connie Rye (East Mississippi Community College), Robert Wise (University of Wisconsin, Oshkosh), Vladimir Jurukovski (Suffolk County Community College), Jean DeSaix (University of North Carolina at Chapel Hill), Jung Choi (Georgia Institute of Technology), Yael Avissar (Rhode Island College) among other contributing authors. Original content by OpenStax (CC BY 4.0; Download for free at http://cnx.org/contents/[email protected] ).

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Results Revealed Following Former Raider's No-Contest Plea in Domestic Violence Case

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• Las Vegas Raiders

Former Las Vegas Raiders edge rusher Chandler Jones has been given his punishment for his domestic violence charge from last year.

According to ESPN, which cited Clark County (Nevada) court documents, Jones pleaded no contest to the charge. As a result, he will not have to serve jail time if he is to obey the conditions of a suspended 90-day sentence. Those conditions include not having any contact with the victim, with the exception of Family Court orders.

Jones was arrested in September after violating a domestic violence temporary protective order. He was charged with a misdemeanor.

The following month, Jones violated the order again and was again arrested.

Per ESPN , Jones had been facing two misdemeanor charges before giving his plea, which dismissed one of the two. The second will be dismissed if he successfully makes it through his suspension without any violations.

The Raiders, who had signed Jones in March 22, released him after that first arrest.

Jones had played 15 games for the Silver and Black in that 2022 campaign, totaling 38 tackles, three for loss, 4.5 sacks, three passes defensed, a forced fumble and a touchdown.

The longtime NFL defensive end had been selected to four Pro Bowls prior to joining the Raiders. He played his first four seasons with the New England Patriots before spending six seasons with the Arizona Cardinals.

Jones, who has been out of the league since being released by Las Vegas, has posted 511 tackles, 121 tackles for loss, 112.0 sacks and two touchdowns in 11 seasons.

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Italy striker Mateo Retegui, speaking post-match, said: "It was a great satisfaction, we are very happy because we played against a team of great quality, demonstrating all our personality after the defeat against Spain.

"A striker always wants to score but we are a team. The important thing today was to draw and get through.

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"When you play with no fear and you have the game in your hands, it's completely different.

"The important thing is the attitude you put on the pitch. At this level, every team is more or less on the same level and the team that is more determined to win finally gets the better (result)."

Zaccagni: Goal was 'indescribable emotion'

Goalscorer Mattia Zaccagni opened up on the emotion of his goal, saying: "It was an indescribable emotion.

"Scoring the goal that helped the team to qualify, I'm so happy.

"(Riccardo) Calafiori gave (me) a fantastic ball, then the hug of the entire team, it was amazing."

Pongracic: Our best 'wasn't enough'

Croatia defender Marin Pongracic said: "It's hard to find the words after this. We are all very disappointed, this was like a big final match for us. We wanted that win more than anything else.

"Of course, we could have been in the better situation before this match, but we weren't, so we had to defeat Italy. We gave everything we could, but it wasn't enough.

"Maybe it's not a coincidence to concede a goal in the last moments of the match in two consecutive matches, especially against Albania. We need to do the deeper analysis of why is this happening. That's why it hurt even more after today.

"We are really sorry to our amazing fans, but we are sorry because of us even more. We know we could have done more than this with what we showed in today's match."

Spalletti: Italy substitutes were 'giants'

Italy boss Luciano Spalletti hailed the impact of his substitutes, saying: "The guys who came on are giants in terms of what they showed.

"Those that played for 10 mins were absolutely crucial, they kept the game in the balance, they did things perfectly."

More from Dalic on Modric substitution

Dalic, asked to explain why he brought off talismanic midfielder Luka Modric, added: "I think he scored a wonderful goal, it would have been a nice goal if he scored from 12 yards (too).

"I didn't want to waste him for more minutes, we needed to freshen things up in terms of personnel, he wasn't in any way tired.

"It was my decision, I wanted to bring someone on who was a bit fresher because Luka had given everything."

Zlatko Dalic: 'It really hurts'

Croatia boss Zlatko Dalic, speaking in his post-match press conference, said: "Yeah, it really hurts, it still hurts and it will still hurt over the coming weeks and months, it's not easy.

"You can't have eight minutes of added time in that game, eight minutes! It's a nonsense, I don't really want to get into it too much, we had a couple of penalties our way, don't want to cause a fuss, but Croatia needs to be respected, recognised, we played for almost three hours.

"Were it Spain, Portugal, Germany, no... As you know FIFA and UEFA, we're a small country, no one gives us too much thought so we have to stand up for ourselves.

"I want to thank the players, I want to thank the fanbase, we are delighted and very proud of them."

Full quotes from Luka Modric: ‘Football was merciless’

Luka Modric labelled football “cruel and merciless” after Croatia were all but eliminated from Euro 2024 by a 98th-minute Italy equaliser.

“We kept battling right until the end but unfortunately football was merciless tonight, football was cruel,” Modric said. “Not only today but also in our last game when we conceded a late goal (in the 95th minute against Albania).

“It’s hard when you lose like this to find the words to describe how you feel. Of course we need to bounce back but that’s the way it is. Perhaps it’s unfair because we all fought for Croatia from the first whistle to the last, the footballing gods don’t always smile on us.

“I’d also like to keep playing for ever, but there’ll probably come a time when I have to hang up my boots,” he added. “I’ll keep playing on but I don’t know for how much longer.”

Luka Modric: ‘Football was merciless’ as Italy equalise in 98th minute against Croatia

Euro 2024, Day 11 - Throwing Beers and Croatia Close to Tears

The heartbreakingly fine margins between success and failure were written across the face of Luka Modric on day 11 of Euro 2024 as Croatia were pretty much eliminated by conceding to Italy in the last act of their game.

All the while the beer cups rained down from the stands, more of that in a bit, on a day that witnessed the start of Barnabas Varga’s road to recovery with surgery after his sickening head clash on Sunday.

Plus, a continuing squabble involving England (who also advanced) and Spain becoming the first team to win three games from three, advancing as Group B winners.

Below, The Athletic 's writers explain the key talking points from today at the Euros.

Euro 2024 day 11 – Throwing beers, Modric close to tears, surgery for Varga, England’s noise

Zlatko Dalic: 'It was a great fight'

Defeated Croatia manager Zlatko Dalic, speaking after the match, said: "Last minute Albania, last minute today. I can only congratulate the guys on the fight, the willingness, the sacrifice they showed. But here it is, it's not our tournament.

"Croatia were good, especially in the first half. We didn't concede a goal, that's what we didn't manage to do against Spain and Albania. I can only congratulate the guys on a great fight.

"We've missed two penalties, we conceded two goals in injury time, that's what it is. A theory about going further?

"Well, we can't influence that, we had the situation in our hands. Thank you to the people who cheered us on, I'm sorry for them, I'm mostly disappointed because of that."

And what about goalscorer Mattia Zaccagni?

The Athletic

That one in the Croatia penalty area, of course, being the key one.

He only entered the match in the 81st minute, but the Lazio winger had quite the impact.

Where did Luka Modric take his touches?

Anatomy of a midfield masterclass.

Reminiscent of Alessandro Del Piero

The manner of Mattia Zaccagni's finish tonight, a right-footed, first-time curling effort from the left side of the penalty area, across the goalkeeper and into the top-right corner had echoes of another famous Italian goal.

Namely, Alessandro Del Piero's stunner against Germany in the 2006 World Cup semi-final.

When asked about the comparison, Zaccagni said: "Alex was my idol. I had his poster in my room and we saw each other before leaving for the Euros. Then we spoke again in recent days too, it was so exciting."

Come-from-behind FC

Bouncebackability, former Crystal Palace manager Iain Dowie used to call it.

That's twice now at this tournament alone Italy have come from behind to avoid defeat, after beating Albania 2-1 after conceding the quickest European Championship goal of all time.

Italy had only come from behind to avoid defeat in a Euros group stage match twice before - a 2-1 win against Bulgaria in 2004 and a 1-1 draw against Romania in 2008.

They've done it twice in three matches in Germany.

A look at the numbers

Croatia outperformed Italy for expected goals (xG) and shots on target, but Italy's goal at the end is the key figure.

Thanks to Duncan Alexander for the graphic.

Spalletti: 'I expect more from my players'

Italy boss Luciano Spalletti, speaking to RAI, said: "When games are decided like this, in the end everything becomes more exciting. No one believed it any more, but the players risked little and kept their heads clear.

"We have to congratulate them on how they reacted. In the first half we were sub-par. If we do so little, we accomplish little. A behaviour where you think about the result without believing you can win it. I expect more from my players. You have to find that balance.

"We have players who have the quality to play these games. But we make mistakes that are too trivial. We have superior qualities than what we have seen. We need to do more."

Di Lorenzo: 'This is a starting point for us'

Italy defender Giovanni Di Lorenzo, speaking to Italian TV channel RAI after the match, said: "It was a tough game, but the important thing was to get through the group, a difficult group. But we're happy, it's nice to draw and go through at the last minute.

"Maybe against Spain we gave this sense of fragility that a great team like ours shouldn't have. We definitely need to grow, even if in these tournaments the time to do so is not enough.

"Certainly in terms of play we can do better, but in terms of attitude we can't say anything. It's a point from which we have to start again."

Ivanusec: 'I am empty'

Modric's team-mate Luka Ivanusec said: “I'm empty, we don't know what to say.

“Until the last minute, we have everything and now I have no words. We are disappointed.”

Defender Marin Pongracic added: “Very sad. The desire was there. We gave them chances, it could have gone the other way.

“After half-time, we got up, took more risks, scored a goal and then, in the end, we concede a goal very cheaply.”

Luka Modric: 'Football is cruel'

Croatia's Luka Modric, speaking after the match, said: "I don't know what to tell you, football is sometimes cruel.

"It has been shown again, but well, what is there is there. We didn't deserve this goal.

"We didn't doubt the fans, we knew they were always with us, thank you. We're sorry that it wasn't that victory to go to the next round."

Cristiano Ronaldo vs Luka Modric

With tonight's goal, as well as becoming the tournament's oldest goalscorer in history, Luka Modric is now just the second player to score at four different European Championship tournaments, along with former Real Madrid team-mate Cristiano Ronaldo.

Ronaldo, currently on five, could make that six if he scores at this tournament.