what is the definition of photosynthesis in plants

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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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• 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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Middle school biology - NGSS

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

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

Key points:

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

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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 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?
• 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 .

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). 

Related: What if humans had photosynthetic skin?

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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Daisy Dobrijevic joined  Space.com  in February 2022 as a reference writer having previously worked for our sister publication  All About Space  magazine as a staff writer. Before joining us, Daisy completed an editorial internship with the BBC Sky at Night Magazine and worked at the  National Space Centre  in Leicester, U.K., where she enjoyed communicating space science to the public. In 2021, Daisy completed a PhD in plant physiology and also holds a Master's in Environmental Science, she is currently based in Nottingham, U.K.

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Science News Explores

Explainer: how photosynthesis works.

Plants make sugar and oxygen with the power of water, carbon dioxide and sunlight

Green plants take in light from the sun and turn water and carbon dioxide into the oxygen we breathe and the sugars we eat.

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By Bethany Brookshire

October 28, 2020 at 6:30 am

Take a deep breath. Then thank a plant. If you eat fruit, vegetables, grains or potatoes, thank a plant too.  Plants and algae provide us with the oxygen we need to survive, as well as the carbohydrates we use for energy. They do it all through photosynthesis.

Photosynthesis is the process of creating sugar and oxygen from carbon dioxide, water and sunlight. It happens through a long series of chemical reactions. But it can be summarized like this: Carbon dioxide, water and light go in. Glucose, water and oxygen come out. (Glucose is a simple sugar.)

Photosynthesis can be split into two processes. The “photo” part refers to reactions triggered by light. “Synthesis” — the making of the sugar — is a separate process called the Calvin cycle.

Both processes happen inside a chloroplast. This is a specialized structure, or organelle, in a plant cell. The structure contains stacks of membranes called thylakoid membranes. That’s where the light reaction begins.

Let the light shine in

When light hits a plant’s leaves, it shines on chloroplasts and into their thylakoid membranes. Those membranes are filled with chlorophyll , a green pigment. This pigment absorbs light energy. Light travels as electromagnetic waves . The wavelength — distance between waves — determines energy level. Some of those wavelengths are visible to us as the colors we see . If a molecule, such as chlorophyll, has the right shape, it can absorb the energy from some wavelengths of light.

Chlorophyll can absorb light we see as blue and red. That’s why we see plants as green. Green is the wavelength plants reflect, not the color they absorb.

While light travels as a wave, it also can be a particle called a photon . Photons have no mass. They do, however, have a small amount of light energy.

When a photon of light from the sun bounces into a leaf, its energy excites a chlorophyll molecule. That photon starts a process that splits a molecule of water. The oxygen atom that splits off from the water instantly bonds with another, creating a molecule of oxygen, or O 2 . The chemical reaction also produces a molecule called ATP and another molecule called NADPH. Both of these allow a cell to store energy. The ATP and NADPH also will take part in the synthesis part of photosynthesis.

Notice that the light reaction makes no sugar. Instead, it supplies energy — stored in the ATP and NADPH — that gets plugged into the Calvin cycle. This is where sugar is made.

But the light reaction does produce something we use: oxygen. All the oxygen we breathe is the result of this step in photosynthesis, carried out by plants and algae (which are not plants ) the world over.

Give me some sugar

The next step takes the energy from the light reaction and applies it to a process called the Calvin cycle. The cycle is named for Melvin Calvin, the man who discovered it.

The Calvin cycle is sometimes also called the dark reaction because none of its steps require light. But it still happens during the day. That’s because it needs the energy produced by the light reaction that comes before it.

While the light reaction takes place in the thylakoid membranes, the ATP and NADPH it produces end up in the stroma. This is the space inside the chloroplast but outside the thylakoid membranes.

The Calvin cycle has four major steps:

• carbon fixation : Here, the plant brings in CO 2 and attaches it to another carbon molecule, using rubisco. This is an enzyme , or chemical that makes reactions move faster. This step is so important that rubisco is the most common protein in a chloroplast — and on Earth. Rubisco attaches the carbon in CO 2 to a five-carbon molecule called ribulose 1,5-bisphosphate (or RuBP). This creates a six-carbon molecule, which immediately splits into two chemicals, each with three carbons.
• reduction : The ATP and NADPH from the light reaction pop in and transform the two three-carbon molecules into two small sugar molecules. The sugar molecules are called G3P. That’s short for glyceraldehyde 3-phosphate (GLIH- sur-AAL-duh-hide 3-FOS-fayt).
• carbohydrate formation : Some of that G3P leaves the cycle to be converted into bigger sugars such as glucose (C 6 H 12 O 6 ).
• regeneration : With more ATP from the continuing light reaction, leftover G3P picks up two more carbons to become RuBP. This RuBP pairs up with rubisco again. They are now ready to start the Calvin cycle again when the next molecule of CO 2 arrives.

At the end of photosynthesis, a plant ends up with glucose (C 6 H 12 O 6 ), oxygen (O 2 ) and water (H 2 O). The glucose molecule goes on to bigger things. It can become part of a long-chain molecule, such as cellulose; that’s the chemical that makes up cell walls. Plants also can store the energy packed in a glucose molecule within larger starch molecules. They can even put the glucose into other sugars — such as fructose — to make a plant’s fruit sweet.

All of these molecules are carbohydrates — chemicals containing carbon, oxygen and hydrogen. (CarbOHydrate makes it easy to remember.) The plant uses the bonds in these chemicals to store energy. But we use the these chemicals too. Carbohydrates are an important part of the foods we eat, particularly grains, potatoes, fruits and vegetables.

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Photosynthesis

What is photosynthesis.

It is the process by which green plants, algae, and certain bacteria convert light energy from the sun into chemical energy that is used to make glucose. The word ‘photosynthesis’ is derived from the Greek word phōs, meaning ‘light’ and synthesis meaning ‘combining together.’

Jan Ingenhousz, the Dutch-born British physician and scientist, discovered the process of photosynthesis.

Where does Photosynthesis Occur

Photosynthesis takes place mainly in the leaves of green plants and also in the stems of herbaceous plants as they also contain chlorophyll. Sometimes it also occurs in roots that contain chlorophyll like in water chestnut and Heart-leaved moonseed. Apart from plants, photosynthesis is also found to occur in blue-green algae.

What Happens During Photosynthesis

It involves a chemical reaction where water, carbon dioxide, chlorophyll, and solar energy are utilized as raw materials (inputs) to produce glucose, oxygen, and water (outputs).

Stages of the Process

Photosynthesis occurs in two stages:

1) The Light-dependent Reaction

• Takes place in the thylakoid membranes of chloroplasts only during the day in the presence of sunlight
• High-energy phosphate molecules adenosine triphosphate ( ATP ) and the reducing agent NADPH are produced with the help of electron transport chain

2) The Light-independent or Dark Reaction ( Calvin cycle )

• Takes place in the stroma of chloroplast in the absence of light that helps to fix carbon
• ATP and NADPH produced in the light reaction are utilized along with carbon dioxide to produce sugar in the form of glucose

Factors Affecting the Rate of Photosynthesis

• Intensity of Light: The higher intensity of light increases the rate of photosynthesis
• Temperature:  Warmer the temperature, higher the rate of photosynthesis. The rate is highest between the temperatures of 25° to 35° C, after which it starts to decrease
• Concentration of Carbon dioxide: Higher concentration of carbon dioxide increases the rate of photosynthesis until it reaches a certain point, beyond which no further effects are found   

Although all the above factors together interact to affect the rate of photosynthesis, each of them individually is also capable of directly influencing the process without the other factors and thus called limiting factors.

Importance of Photosynthesis

It serves two main purposes that are essential to support life on earth:

• Producing food for organisms that depend on others for their nutrition such as humans along with all other animals
• Synthesizing oxygen by replacing carbon dioxide in the atmosphere

Ans. Photosynthesis is an endothermic reaction because it absorbs the heat of the sun to carry out the process.

Ans. The oxygen in photosynthesis comes from splitting the water molecules.

Ans. Chlorophyll is the main light-absorbing pigment in photosynthesis.

Ans. The role of water is to provide oxygen in the form of oxygen gas to the atmosphere.

Ans. Sunlight is the source of energy that drives photosynthesis.

Ans. The easiest way to measure the rate of photosynthesis is to quantify the carbon dioxide or oxygen levels using a data logger. The rate of photosynthesis can also be measured by determining the increase in the plant ’s biomass (weight).

Ans. Photosynthesis is an energy-requiring process occurring only in green plants, algae, and certain bacteria that utilizes carbon dioxide and water to produce food in the form of carbohydrates. In contrast, cellular respiration is an energy-releasing process found in all living organisms where oxygen and glucose are utilized to produce carbon dioxide and water.

Ans. Glucose produced in photosynthesis is used in cellular respiration to make ATP.

Article was last reviewed on Tuesday, April 21, 2020

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Biology Notes Online

Photosynthesis – Definition, Steps, Equation, Process, Diagram, Examples

Table of Contents

What is Photosynthesis?

• Photosynthesis is a fundamental biochemical process that harnesses the energy of light to synthesize glucose molecules. This intricate mechanism can be delineated into two primary stages. Initially, light energy is captured and transformed into chemical energy, stored within the molecules of adenosine triphosphate ( ATP ) and nicotinamide adenine dinucleotide phosphate (NADPH).
• Subsequently, these energy-rich cofactors participate in the Calvin Cycle, a series of reactions that facilitate the synthesis of organic molecules by assimilating carbon atoms from carbon dioxide (CO2). These organic molecules can either be utilized by mitochondria to generate ATP or amalgamated to yield glucose, sucrose, and other carbohydrates.
• Scientifically defined, photosynthesis is a cellular process employed by a myriad of organisms to transmute light energy into chemical energy. This stored chemical energy is embedded within organic compounds, which, upon metabolism via cellular respiration, release energy essential for the organism’s functions.
• Predominantly, the term “photosynthesis” alludes to oxygenic photosynthesis, characterized by the production of oxygen as a byproduct and the storage of some resultant chemical energy within carbohydrate molecules, including sugars, starch, and cellulose .
• This form of photosynthesis is executed by a majority of plants, algae, and cyanobacteria, collectively termed as photoautotrophs. Notably, photosynthesis plays a pivotal role in sustaining Earth’s atmospheric oxygen levels and furnishing the majority of biological energy requisite for Earth’s complex life forms.
• However, certain bacteria undergo anoxygenic photosynthesis, utilizing bacteriochlorophyll to cleave hydrogen sulfide, leading to the production of sulfur instead of oxygen. Furthermore, specific Archaea , such as Halobacterium, engage in a distinct form of non-carbon-fixing anoxygenic photosynthesis, leveraging simpler photopigments like retinal to absorb light and directly synthesize ATP . This archaic form of photosynthesis is postulated to be one of the earliest evolutionary adaptations on Earth.
• Regardless of the organism or method, photosynthesis invariably commences with the absorption of light energy by proteins known as reaction centers, which contain photosynthetic pigments or chromophores. In plants, these proteins, predominantly chlorophyll, are housed within organelles termed chloroplasts. During the light-dependent reactions, electrons are extracted from substances like water, resulting in the release of oxygen gas. The liberated hydrogen aids in the formation of NADPH and ATP .
• In plants, algae, and cyanobacteria, the Calvin cycle subsequently facilitates the synthesis of sugars. Here, atmospheric carbon dioxide is integrated into pre-existing organic carbon compounds, utilizing the ATP and NADPH generated earlier. In certain bacteria, alternative mechanisms achieve carbohydrate synthesis.
• Historically, the earliest photosynthetic organisms likely utilized reducing agents such as hydrogen or hydrogen sulfide. The advent of cyanobacteria marked a significant evolutionary milestone, as the surplus oxygen they generated significantly influenced Earth’s atmospheric composition, paving the way for the evolution of complex life forms.
• Presently, photosynthesis captures energy at an astounding rate of approximately 130 terawatts, surpassing the current global power consumption. Furthermore, photosynthetic organisms assimilate between 100–115 billion tons of carbon annually.
• In conclusion, photosynthesis is not only a cornerstone of life on Earth but also plays a crucial role in global climate processes by sequestering carbon dioxide. This intricate process, first identified by Jan Ingenhousz in 1779, remains a testament to nature’s ingenuity and efficiency.

Definition of Photosynthesis

Photosynthesis is the biological process by which plants, algae, and certain bacteria convert light energy into chemical energy, producing oxygen and organic compounds, primarily glucose, from carbon dioxide and water.

Experimental History

The intricate process of photosynthesis, which underpins life on Earth, has been the subject of extensive scientific inquiry over the centuries. This journey of discovery, refinement, and development has been marked by the contributions of numerous scientists, each building upon the work of their predecessors. Below is a summarized account of the experimental history of photosynthesis:

Where Does Photosynthesis take place?

Photosynthesis primarily occurs in the chloroplasts, specialized organelles found predominantly in plant leaves. These chloroplasts belong to a category of organelles known as plastids, which are membrane-bound structures responsible for various vital cellular functions.

• Chloroplast Structure : Chloroplasts are a type of primary plastid characterized by a double-membrane structure. They house the essential green pigment, chlorophyll, which plays a pivotal role in capturing light energy. In contrast, secondary plastids, found in certain plankton species, possess multiple membranes.
• Role of Chlorophyll : Chlorophyll pigments are responsible for absorbing light energy from the sun. Upon absorption, a chlorophyll molecule releases an electron, initiating the process of converting light energy into chemical energy.
• Reaction Centers : These are specialized complexes composed of pigments and proteins. They serve as the primary sites where light energy is transformed into chemical energy, marking the onset of electron transfer. The energy captured by the reaction centers is crucial for driving the subsequent biochemical reactions of photosynthesis.

In summary, photosynthesis is a complex process that takes place within the chloroplasts of plant cells. The chlorophyll pigments housed within these organelles are instrumental in capturing and converting light energy into a form that can be utilized by the plant for growth and sustenance.

Photosynthesis: a two-stage process

Photosynthesis, a fundamental biochemical process, can be delineated into two distinct stages. Contrary to the traditional classification of these stages as ‘light’ and ‘dark’ reactions, contemporary scientific understanding emphasizes that both stages are influenced by light, albeit in different capacities.

1. Photochemical Reaction Process (Light-Dependent Reactions):

In this initial stage, light energy, primarily from the sun, is harnessed and converted into chemical energy in the form of adenosine triphosphate ( ATP ). This process, known as photophosphorylation, is contingent upon the presence of light. During this phase:

• Photons are absorbed by photosynthetic pigments, initiating a series of electron transfer events.
• The energy derived from these events drives the synthesis of ATP and the electron carrier molecule, nicotinamide adenine dinucleotide phosphate (NADPH).
• Oxygen is released as a byproduct when water molecules are split.

2. Carbon Fixation Process (Light-Independent Reactions):

While this stage does not directly utilize light energy, it is influenced by the products of the light-dependent reactions. The primary objective here is the conversion of inorganic carbon into organic compounds. This energy-consuming, endergonic process can manifest in two distinct pathways:

• Carbon dioxide from the atmosphere is captured and integrated into existing organic molecules.
• The ATP and NADPH produced in the light-dependent reactions provide the energy and electrons, respectively, for the synthesis of glucose and other carbohydrates.
• Non-Calvin Cycle: This alternative pathway is exclusive to certain anoxygenic photosynthetic organisms. It diverges from the Calvin cycle in its mechanism of carbon fixation and the compounds produced.

In summation, photosynthesis is a two-stage process wherein light energy is first converted into chemical energy, which subsequently powers the synthesis of organic compounds from inorganic carbon. Both stages, while functionally distinct, are interdependent and collectively contribute to the sustenance of life on Earth.

Photosynthesis equations/reactions/formula

Photosynthesis, a fundamental biochemical process, varies between green plants and sulfur bacteria in terms of the reactants used and the products formed.

Oxygenic Photosynthesis in Plants:

In green plants, photosynthesis utilizes water and carbon dioxide, harnessing solar energy to produce glucose and oxygen. The overarching equation representing this process is:

6 CO 2 ​+6 H 2​ O +light energy→ C 6 ​ H 12 ​ O 6 ​+6 O 2​

Alternatively, it can be represented as:

6 CO 2 ​+12 H 2 ​ O +light energy→ C 6 ​ H 12 ​ O 6 ​+6 O 2​ +6 H 2 ​ O

This equation signifies that six molecules of carbon dioxide and twelve molecules of water, in the presence of light energy, yield one molecule of glucose, six molecules of oxygen, and six molecules of water. It’s noteworthy that while a triose (3-carbon molecule) is the direct product of photosynthesis, glucose, a hexose, is often depicted as the end product due to its foundational role in cellular processes. Additionally, the oxygen produced serves dual purposes: it is utilized by the plant during oxidative phosphorylation and is also released into the atmosphere, facilitating aerobic respiration in other organisms.

Anoxygenic Photosynthesis in Sulfur Bacteria:

Sulfur bacteria employ a distinct form of photosynthesis. Instead of water, they use hydrogen sulfide in conjunction with carbon dioxide. The general equation for this process is:

CO 2 ​+2 H 2 ​ S +light energy→( CH 2 ​ O )+ H 2 ​ O +2 S

This equation illustrates that carbon dioxide and hydrogen sulfide, under the influence of light energy, produce carbohydrates, water, and elemental sulfur.

In summation, photosynthesis, whether in plants or sulfur bacteria, is a series of intricate reactions that convert simple molecules into energy-rich compounds, using light as the primary energy source. The specific reactants and products differ based on the organism, but the core principle of harnessing light energy remains consistent.

Types of Photosynthesis

Photosynthesis, the fundamental process by which organisms convert light energy into chemical energy, manifests in various forms across different species. These diverse pathways are tailored to the specific environmental conditions and metabolic needs of the organisms. Here, we delve into the primary types of photosynthesis and their distinctive characteristics.

• Organisms : Predominantly found in cereals like wheat and rice, as well as in cotton, potatoes, and soybeans.
• Process : The enzyme Rubisco facilitates the fixation of CO2, producing a three-carbon molecule, 3-phosphoglyceric acid (3-PGA).
• Organisms : Plants such as sugarcane and maize.
• Process : CO2 is initially fixed into a four-carbon compound, oxaloacetate, which is subsequently converted to malate. This malate is transported to the bundle sheath cells, where it releases CO2. This CO2 is then utilized in the Calvin cycle, akin to the C3 pathway. Notably, C4 plants exhibit enhanced water-use efficiency in hot, arid conditions.
• Organisms : Adapted to extremely arid environments, plants like cacti and pineapples employ this pathway.
• Process : To mitigate water loss, these plants open their stomata during the cooler nighttime hours, absorbing CO2. This CO2 is fixed into organic acids, which are stored until daylight, when they are utilized in the light-dependent reactions of photosynthesis.
• Prokaryotic Photosynthesis : Executed by organisms without a defined nucleus, such as certain bacteria.
• Eukaryotic Photosynthesis : Conducted by organisms with a well-defined nucleus, including protists and green plants.
• Organisms : Cyanobacteria (prokaryotic) and protists like diatoms, dinoflagellates, and Euglena (eukaryotic). Additionally, green plants, spanning from algae to angiosperms, employ this pathway.
• Characteristic : Oxygen is evolved as a byproduct.
• Organisms : Exclusively prokaryotic, including green sulfur bacteria and purple bacteria.
• Characteristic : Oxygen is not released during the process.

In summary, photosynthesis, though universally critical for life on Earth, manifests in a myriad of forms, each tailored to the unique needs and environments of the photosynthesizing organisms.

Photosynthetic pigments

Photosynthetic pigments are specialized molecules that absorb and harness light energy, facilitating the conversion of this energy into chemical energy during the process of photosynthesis. These pigments are pivotal for the efficient absorption of light across various wavelengths.

1. Chlorophyll: Chlorophyll, predominantly green in color, is the primary pigment responsible for capturing light energy. Its salient features include:

• Nature: It is a lipid-based molecule.
• Location: Predominantly found within the thylakoid membranes of chloroplasts.
• Types: Several variants exist, including chlorophyll-a, b, c, and d. Among these, chlorophyll-a is the primary photosynthetic pigment.
• Structure: Chlorophyll-a, b, and d are derivatives of “chlorin,” while chlorophyll-c is a “porphyrin” derivative. A unique feature is the presence of a central magnesium ion (Mg^2+).
• Function: Chlorophyll is instrumental in capturing and storing solar energy, and it plays a pivotal role in the photochemical reactions of photosynthesis.

2. Carotenoids: Carotenoids, often yellow, red, or purple, work synergistically with chlorophyll. Their key characteristics are:

• Nature: These are lipid-soluble molecules.
• Types: Over 150 variants of carotenoids have been identified.
• Forms: They exist as simple hydrocarbons (e.g., beta-carotene) or oxygenated hydrocarbons (e.g., lutein).
• Function: Carotenoids assist in energy transfer, act as free-radical scavengers, and provide photoprotection by quenching excess energy.

3. Phycobilins: Distinct from chlorophyll and carotenoids, phycobilins are present in specific oxygenic photosynthetic organisms, particularly cyanobacteria and red algae.

• Types: Notable variants include Phycoerythrobilin, Phycocyanobilins, and Allophycocyanobilins.
• Structure: These pigments possess a tetrapyrrole structure and do not require magnesium ions.
• Location: Being water-soluble, phycobilins, in conjunction with proteins, form phycobiliproteins. These proteins aggregate into clusters known as phycobilisomes, which adhere to membranes.
• Function: Phycobilins are primarily involved in resonance energy transfer.

4. Bacteriorhodopsin: Exclusive to halobacteria, bacteriorhodopsin is a pigment that consists of a protein linked to a retinal prosthetic group. It plays a role in light absorption, leading to proton expulsion from the cell.

In summary, photosynthetic pigments are integral to the process of photosynthesis, ensuring efficient light absorption and energy conversion. Each pigment type has a distinct role and absorption spectrum, collectively ensuring that a broad range of light wavelengths is harnessed for photosynthesis.

Structure Of Chlorophyll

Chlorophyll, the quintessential green pigment in plants, possesses a unique molecular structure that facilitates its primary function: the absorption of sunlight for photosynthesis.

• Central Composition : At the core of chlorophyll’s structure lies a magnesium atom, encircled by four nitrogen atoms. This configuration is pivotal for its light-absorbing properties.
• Hydrocarbon Tail : Attached to this core is a hydrocarbon tail, which anchors the molecule to the thylakoid membrane within the chloroplasts.
• Chlorophyll-b : This assists chlorophyll-a in capturing light energy and is found alongside it in many plants.
• Chlorophyll-c1 and c2 : Typically found in certain algae species.
• Chlorophyll-d : Present in some cyanobacteria, it absorbs energy from different wavelengths of light compared to chlorophyll-a.
• Chlorophyll-f : Unique for its ability to absorb near-infrared light, making it more efficient than chlorophyll-a in certain conditions.
• Distribution : While green plants predominantly contain chlorophyll-a and chlorophyll-b, other photosynthesizing organisms, like certain algae and cyanobacteria, have the other variants, allowing them to optimize light absorption in diverse environments.

In essence, the structure of chlorophyll, with its central magnesium atom and various molecular variants, is ingeniously designed to maximize the absorption of sunlight, driving the life-sustaining process of photosynthesis across diverse organisms.

Factors affecting photosynthesis

Photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy, is influenced by a myriad of both external and internal factors. A comprehensive understanding of these factors is pivotal for optimizing the photosynthetic efficiency of plants.

1. Light Intensity, Quality, and Duration:

• Sciophytes: Flourish under diffused light conditions. (e.g., Oxalis)
• Heliophytes: Thrive under direct sunlight. (e.g., Dalbergia)
• Quality: Photosynthetically Active Radiation (PAR) denotes the fraction of light that actively participates in photosynthesis, typically ranging between 400-700nm in wavelength.
• Duration: While the duration of light exposure doesn’t directly alter the rate of photosynthesis, it does influence the total photosynthetic output.

2. Temperature:

Temperature plays a pivotal role in enzymatic activities associated with photosynthesis. For C3 plants, the optimal temperature range lies between 20-25°C, while C4 plants exhibit peak efficiency between 30-45°C. Beyond these ranges, enzymatic activities can diminish, potentially hampering the photosynthetic rate.

3. Carbon Dioxide Concentration:

Carbon dioxide (CO2) is a primary substrate in the photosynthetic process. An increase in its concentration can enhance the photosynthetic rate in C3 plants. However, C4 plants, equipped with a CO2 enrichment mechanism, exhibit a plateau in their photosynthetic rate even with elevated CO2 levels. The CO2 Compensation Point represents a threshold where the illuminated plant part ceases to absorb CO2.

4. Water Availability:

Water is indispensable for photosynthesis, participating in both light-dependent and light-independent reactions. A deficiency can impede the electron flow in Photosystem II and disrupt the Calvin cycle, thereby affecting the overall photosynthetic efficiency.

5. Genetic Factors:

Intrinsic genetic factors can also influence photosynthesis. Variations in genes encoding for photosynthetic machinery can lead to differences in their efficiency and functionality. Some species have evolved unique mechanisms to enhance photosynthetic efficiency, adapting to their specific environmental conditions.

In conclusion, photosynthesis is a multifaceted process influenced by a confluence of environmental and genetic factors. Understanding these factors and their interplay can provide insights into optimizing photosynthetic efficiency, with potential implications for agriculture and bioenergy production.

Photosynthetic Membranes and Organelles

Photosynthesis, the fundamental process by which energy from sunlight is converted into chemical energy, is facilitated by specific pigment molecules that absorb photons of light. The efficiency of this process is contingent upon the absorption of light within a precise wavelength range, ensuring the optimal energy required for photosynthesis.

To achieve this specificity in light absorption, phototrophic organisms have evolved specialized structures known as reaction center proteins. These proteins house the pigment molecules and are strategically positioned within the membranes of the organisms to optimize light absorption.

• In prokaryotes, the photosynthetic machinery is embedded directly within the cell or thylakoid membranes present in the cytosol.
• Unlike eukaryotes, prokaryotes lack specialized organelles like chloroplasts. Instead, their photosystems are integrated within the cellular architecture, ensuring efficient light capture and energy conversion.
• Eukaryotic organisms, such as green plants, possess specialized organelles known as chloroplasts. These chloroplasts are the hubs of photosynthetic activity.
• Within the chloroplasts, the thylakoid membranes house the photosystems. These membranes are laden with chlorophyll and other pigments, facilitating the absorption of light and the subsequent conversion of this energy into chemical forms.

In essence, the spatial organization of pigment molecules within specific membranes and organelles is a testament to the evolutionary adaptations of organisms to harness light energy efficiently. This intricate arrangement ensures that photosynthesis proceeds optimally, sustaining life on Earth.

Organelle for Photosynthesis

• The chloroplast is a pivotal organelle in eukaryotic cells, serving as the primary site for photosynthesis. Eukaryotic organisms, which encompass a diverse range of life forms, rely on chloroplasts to harness light energy and convert it into chemical energy.
• A typical plant cell is endowed with approximately 10 to 100 chloroplasts, underscoring their significance in the photosynthetic process. Delving deeper into the structure of the chloroplast, one encounters the thylakoids. These are specialized, membrane-bound compartments housed within the chloroplast.
• The thylakoid is not exclusive to eukaryotic chloroplasts; it is also found in the cytosol of cyanobacteria. However, it’s worth noting that while cyanobacteria possess thylakoids, they lack chloroplasts as a distinct organelle. The thylakoid is instrumental in the initial stages of photosynthesis, specifically the light-dependent or photochemical reactions.
• This compartment is intricately structured, comprising the membrane, lumen, and lamellae. Embedded within the thylakoid membranes are chlorophyll molecules, the green pigments responsible for capturing light energy.
• These molecules play a central role in the absorption and conversion of light energy, initiating the cascade of reactions that culminate in the synthesis of organic molecules. In summary, the chloroplast, with its resident thylakoids, stands as the cornerstone of photosynthesis in eukaryotic organisms, orchestrating the intricate processes that transform light into life-sustaining energy.

Process/ Steps of Photosynthesis – Mechanisms of Photosynthesis

Photosynthesis, a cornerstone of plant physiology, is a systematic process that facilitates the conversion of light energy into chemical energy stored in organic molecules. This intricate mechanism can be elucidated through the following sequential stages:

• Light Absorption: Within the chloroplasts, thylakoid membranes house chlorophyll molecules and other pigments. These molecules are adept at capturing light energy. Once absorbed, this energy facilitates the extraction of electrons from a donor, typically water. This electron removal results in the formation of oxygen. The primary electron acceptor in this phase is quinine (Q), akin to CoQ present in the electron transport chain.
• Electron Transport: Post the initial absorption, the electrons are relayed from the primary electron acceptor to a series of molecular intermediaries located within the thylakoid membrane. The culmination of this transfer sees the electrons being accepted by NADP+, the terminal electron acceptor. Concurrently, as electrons traverse the membrane, protons are actively extricated, engendering a proton gradient across the membrane.
• ATP Synthesis: Leveraging the established proton gradient, protons traverse from the thylakoid lumen back to the stroma via the F0F1 complex. This movement is instrumental in the phosphorylation of ADP, resulting in the generation of ATP . This phase mirrors the ATP synthesis observed in the mitochondrial electron transport chain.
• Carbon Reduction: With the energy and electrons furnished by NADP and ATP from the preceding steps, carbon dioxide undergoes a reduction process, culminating in the formation of six-carbon sugar molecules. It’s imperative to note that while the initial three stages are contingent on light, rendering them “light reactions”, the carbon reduction step operates independently of light, earning it the designation of “dark reactions”.

In summation, photosynthesis is a meticulously orchestrated sequence of events, harmonizing light-dependent and light-independent reactions to produce organic compounds vital for plant sustenance and growth.

Types/ Stages/ Parts of photosynthesis

Photosynthesis can be split into two stages that are based on the use of light energy

1. Light-dependent reactions

Photosynthesis, a pivotal biochemical process, encompasses a series of reactions that convert light energy into chemical energy. The light-dependent reactions, as the name suggests, are contingent on the presence of light and primarily transpire within the thylakoid membranes of chloroplasts. These reactions can be systematically delineated into the following stages:

1. Photon Absorption and Light Harvesting

The initial phase involves the capture of photons by chlorophyll molecules, accessory pigments, and associated proteins, collectively termed photoreceptors. These photoreceptors are organized into intricate assemblies, comprising a photosynthetic reaction center, core antenna complexes, and light-harvesting complexes (LHC). The core antenna and LHC, constituted by accessory pigments and chlorophyll-bound proteins, function as photon traps, capturing diverse wavelengths of light. Sequentially, the absorbed photon energy is channeled towards the photosynthetic reaction center.

Two distinct photosynthetic reaction centers are present in plants, green algae, and cyanobacteria:

• Photosystem I (PSI): Primarily utilizing chlorophyll a, PSI is excited by light with a peak wavelength of 700 nanometers (P700).
• Photosystem II (PSII): Incorporating both chlorophyll a and b, PSII can absorb light up to a wavelength of 680 nanometers (P680).

2. Electron Transport Dynamics:

Photon absorption culminates in the elevation of an electron to a heightened energy state, engendering a negatively charged radical. This unstable state prompts the electron’s spontaneous transfer to a proximate acceptor molecule, rendering the photoreceptor positively charged. Subsequent replenishment of the photoreceptor is achieved through electrons derived either from water or another electron transfer chain.

Electron transfer ensues through a series of complexes:

• PSI (Plastocyanin-Ferredoxin Oxidoreductase): Here, the excited electron from P700 is relayed to plastocyanin (PC), which subsequently donates the electron to ferredoxin (Fd). Concurrently, NADP+ is reduced to NADPH in the stroma.
• PSII: The excited P680 electron is sequentially transferred to pheophytin and plastoquinone. The resultant plastoquinol diffuses to the Cytochrome b6f complex. The oxygen-evolving complex (OEC) facilitates the replenishment of P680 by catalyzing water oxidation, releasing oxygen and protons.
• Cytochrome b6f Complex: Serving as a bridge between the photosystems, this complex facilitates linear electron flow, adhering to the Z scheme. The electron transfer is concomitant with proton translocation, engendering a proton gradient vital for ATP synthesis.

3. Photophosphorylation:

Two pathways exist for ATP synthesis:

• Z Scheme Pathway (Non-Cyclic Photophosphorylation): The proton gradient established during electron transfer drives ATP synthesis via ATP-H+ synthase, converting ADP to ATP .
• Cyclic Photophosphorylation: Here, electron flow is circumscribed between PSI and the Cytochrome b6f complex. The resultant proton gradient similarly facilitates ATP synthesis.

In essence, light-dependent reactions are a harmonious interplay of photon absorption, electron transport, and ATP synthesis, laying the foundation for the subsequent light-independent reactions of photosynthesis.

Wavelengths of light involved and their absorption

Light, a fundamental driver of photosynthesis, is composed of a spectrum of wavelengths, each with its distinct properties. The entirety of this spectrum, spanning from 390 to 760 nanometers (nm), constitutes the visible light spectrum perceivable by the human eye. However, not all these wavelengths are equivalently harnessed by photosynthetic organisms.

Within the broad spectrum of visible light lies a critical subset termed PAR, or Photosynthetically Active Radiation. This segment, ranging from 400 to 760 nm, is of paramount importance to photosynthetic processes. Within PAR, specific wavelengths play distinct roles:

• Blue Light (470-500 nm): This segment of the spectrum is actively absorbed and utilized by photosynthetic organisms. It plays a pivotal role in phototropic responses and chlorophyll production, thereby influencing plant growth and development.
• Red Light (660-760 nm): Another crucial segment for photosynthesis, red light is absorbed efficiently by chlorophyll pigments, driving the photosynthetic process.
• Green Light (500-580 nm): Contrary to the active absorption of blue and red lights, green light is predominantly reflected by plants. This reflection imparts the characteristic green hue to most plants. It’s worth noting that while the green light is majorly reflected, it is not entirely unused; a fraction is absorbed, albeit less efficiently than blue or red light.
• Blue-Green Light: While the spectrum does encompass blue-green wavelengths, it is the blue light, not the blue-green, that is harnessed for photosynthesis.

In summation, while the visible spectrum is vast, photosynthetic organisms exhibit selectivity in the wavelengths they absorb and utilize. This selective absorption and reflection not only drive the photosynthetic process but also influence the very appearance of plants in our environment.

Absorption spectrum and action spectrum

In the realm of photosynthesis, understanding the interaction between light and pigments is paramount. Two critical spectra, the absorption spectrum and the action spectrum, provide insights into this interaction. These spectra elucidate the efficiency of different wavelengths in the photosynthetic process and the role of specific pigments.

• Definition: The absorption spectrum is a graphical representation that delineates the efficiency with which a specific pigment absorbs various wavelengths of light.
• Graphical Representation: On the X-axis, the graph plots the wavelengths of light (measured in nanometers/nm), while the Y-axis represents the percentage of light absorption by the pigment.
• Characteristics: Each pigment possesses a unique absorption spectrum, making it a signature representation of that pigment. For instance, chlorophyll-a and chlorophyll-b have distinct absorption peaks, indicating their preferential absorption of specific wavelengths.
• Example: Chlorophyll-a predominantly absorbs light at 430 nm (blue) and 660 nm (red), with a higher absorption efficiency at 660 nm. In contrast, chlorophyll-b exhibits optimal absorption at 430 nm (blue) and 660 nm (red), with a pronounced peak at 430 nm.
• Definition: The action spectrum offers a depiction of the effectiveness of different light wavelengths in instigating the photosynthetic process.
• Graphical Representation: The X-axis plots the wavelengths of light (in nanometers/nm), while the Y-axis showcases the rate of photosynthesis, typically quantified by the amount of oxygen released.
• Interrelation with Absorption Spectrum: Overlaying the action spectrum with the absorption spectrum of a pigment can elucidate the contribution of specific wavelengths to photosynthetic efficiency and productivity.
• Significance: While the absorption spectrum can be determined for any photosynthetic pigment, the action spectrum is specifically associated with the primary photochemical reaction-performing pigment, chlorophyll-a. This pigment is located at the reaction center, where the evolution of oxygen gas, indicative of photosynthetic activity, predominantly occurs. Given its direct link to the excitation of the chlorophyll-a molecule, the action spectrum is exclusively attributed to this pigment.

In summary, while the absorption spectrum provides insights into the light-absorbing capabilities of pigments, the action spectrum reveals the functional efficacy of these absorbed wavelengths in driving photosynthesis. Together, these spectra offer a comprehensive understanding of the intricate interplay between light and photosynthetic pigments.

What actually happens in the Light-dependent reaction

The light-dependent reaction is a pivotal phase in photosynthesis, transpiring within the chloroplasts. This process is initiated by the absorption of light energy and culminates in the synthesis of ATP and NADPH, which are quintessential for the subsequent light-independent reactions. Here’s a detailed elucidation of the events that transpire during the light-dependent reaction:

• Upon the absorption of a photon by a chlorophyll molecule, specifically P680, the molecule becomes photoexcited and releases an electron.
• This event marks the commencement of the photochemical electron flow.
• The excited electron is initially relayed to the D1/D2 protein complex.
• Subsequently, it is transferred to a modified chlorophyll variant and then to “pheophytin.”
• The electron journey continues as it moves to plastoquinone A and eventually to plastoquinone B.
• The orchestrated electron flow sets in motion an electron transport chain, which plays a pivotal role in the light-dependent reactions.
• One of the primary outcomes of this electron flow is the reduction of NADP to NADPH. This molecule, NADPH, is instrumental in the subsequent light-independent reactions of photosynthesis.
• Concurrently, the electron flow engenders a proton gradient across the chloroplast membrane.
• The established proton gradient is harnessed by the ATP synthase enzyme.
• Utilizing this gradient, ATP synthase facilitates the phosphorylation of ADP to generate ATP .
• The synthesized ATP serves as an energy reservoir for the ensuing light-independent reactions.

In essence, the light-dependent reaction is a meticulously orchestrated sequence of events that harnesses light energy to produce ATP and NADPH. These molecules are indispensable for the sustenance of the photosynthetic process and the plant’s overall energy requirements.

Water photolysis

Water photolysis, also known as the oxygen-evolving process, is a fundamental mechanism within the photosynthetic pathway. This process is responsible for replenishing the electron deficit experienced by the chlorophyll molecule during the initial stages of photosynthesis. Here’s a comprehensive overview of water photolysis:

• During photosynthesis, the chlorophyll molecule loses an electron upon photon absorption. To sustain the continuity of the photosynthetic electron transport chain, this electron deficit must be addressed.
• The mechanism that compensates for this electron loss is the photolysis of water molecules, facilitated by the “oxygen-evolving complex” situated in the thylakoid membrane.
• As a consequence of water photolysis, oxygen is evolved. This process not only replenishes the lost electron to the chlorophyll molecule but also results in the liberation of oxygen gas, a byproduct of photosynthesis.
• The origin of the oxygen released during photosynthesis was a subject of scientific debate. Initial hypotheses posited that the oxygen atom from CO2 might be the source of the evolved oxygen.
• However, through collaborative research, the mystery was unraveled. C.B. Van Niel, studying purple photosynthetic bacteria, provided indirect evidence suggesting that the oxygen source was water molecules, not CO2.
• This assertion was further corroborated by Ruben, Hassid, and Kamen, who employed isotopic studies to furnish direct evidence that the oxygen evolved during photosynthesis indeed originates from H2O molecules.
• The photolysis process involves the hydrolysis of two water molecules, culminating in the release of one molecule of oxygen gas. This can be represented by the following equation for the light-dependent reactions: 2 H 2​ O +2 N A D P ++3 A D P +3 P i + l i g h t →2 N A D P H +2 H ++3 A TP + O 2​

In essence, water photolysis is a pivotal process in photosynthesis, ensuring the continuity of the electron transport chain and facilitating the release of oxygen, which is vital for aerobic life forms on Earth.

In the realm of photosynthesis, the photochemical reactions can be categorized into two primary types: cyclic and non-cyclic reactions. These reactions are distinguished by the involvement and flow of electrons through photosystems.

• This reaction involves solely Photosystem I (PS1).
• Upon photon absorption, the P700 chlorophyll molecule in PS1 becomes excited. The excited electron then traverses a sequence of molecules: from Fe-S to Ferredoxin, followed by Plastoquinone, the Cytochrome b6f complex, and finally to Plastocyanin.
• Given the exclusive involvement of PS1, the electron flow forms a loop, rendering it cyclic. This process culminates in what is termed cyclic phosphorylation.
• This reaction predominantly occurs in the stroma lamellae, especially when light with a wavelength exceeding 680nm is available.
• This reaction encompasses both Photosystem I (PS1) and Photosystem II (PS2).
• In PS2, the absorption of a photon excites the P680 chlorophyll molecule. This excitement leads to the loss of an electron, which is subsequently transferred to pheophytin.
• The electron then embarks on a unique trajectory, often visualized as a zigzag or ‘Z’ pattern, hence the name “Z-Scheme.”
• Within this Z-Scheme, the electron undergoes a series of redox reactions, culminating in the reduction of NADP+ to NADPH.
• Concurrently, the chemiosmotic potential is established by pumping protons across the membrane into the thylakoid lumen. This gradient drives the synthesis of ATP .

In summary, the Z-Scheme is a crucial component of the non-cyclic photochemical reactions in photosynthesis. It delineates the intricate electron flow through both photosystems, facilitating the production of essential energy molecules, NADPH and ATP , vital for the subsequent stages of photosynthesis.

Cyclic vs. Non-cyclic phosphorylation

In the intricate process of photosynthesis, photochemical reactions play a pivotal role. These reactions can be broadly categorized into cyclic and non-cyclic phosphorylation. Each type has distinct characteristics and functions. Here’s a detailed comparison between the two:

Key Insights:

• Cyclic Phosphorylation: This process involves only Photosystem I (PS1). As the name suggests, the electron flow is cyclic, meaning the electrons return to their original position after completing the cycle. Notably, this process does not lead to the oxidation of water or the generation of oxygen gas. Its primary function is to produce ATP .
• Non-cyclic Phosphorylation: This is a more complex process involving both Photosystem I (PS1) and Photosystem II (PS2). Here, electrons are transferred from water molecules to NADP+, resulting in the production of NADPH. This process leads to the oxidation of water, releasing oxygen gas as a byproduct. Both ATP and NADPH are produced, which are essential for the subsequent stages of photosynthesis.

In essence, while both cyclic and non-cyclic phosphorylation contribute to the production of ATP , only non-cyclic phosphorylation results in the generation of NADPH and oxygen gas, making it integral to the overall photosynthetic process.

2. Light independent reactions (Calvin cycle)

The Calvin Cycle, also known as the light-independent reactions, is a crucial phase of photosynthesis that operates in the stroma of chloroplasts. Contrary to its name, this cycle doesn’t directly rely on light; however, it is dependent on the ATP and NADPH produced during the light-dependent reactions.

• Carbon Fixation: The cycle commences with the fixation of a single carbon dioxide molecule to a five-carbon sugar called ribulose 1,5-bisphosphate. This reaction is facilitated by the enzyme ribulose 1,5-bisphosphate carboxylase, commonly referred to as rubisco. The immediate product is an unstable six-carbon compound, which rapidly splits into two molecules of 3-phosphoglycerate.
• Reduction Phase: The 3-phosphoglycerate molecules undergo a series of enzymatic reactions. Initially, ATP donates a phosphate group to 3-phosphoglycerate, forming 1,3-bisphosphoglycerate. Subsequently, NADPH provides electrons, converting 1,3-bisphosphoglycerate into glyceraldehyde 3-phosphate. While a portion of the produced glyceraldehyde 3-phosphate contributes to the synthesis of glucose and other sugars, the majority is utilized to regenerate ribulose 1,5-bisphosphate.
• Regeneration of Ribulose 1,5-bisphosphate: The remaining glyceraldehyde 3-phosphate undergoes a complex series of enzymatic reactions, resulting in the production of ribulose 1,5-bisphosphate. This regeneration ensures the continuity of the Calvin Cycle.

Overall Reaction: 3 C O 2​+9 A TP +6 N A D P H +6 H +→ g l ycer a l d e h y d e −3− p h os p ha t e ( G 3 P )+9 A D P +8 P i +6 N A D P ++3 H 2​ O

To synthesize one molecule of glucose, which contains six carbon atoms, the Calvin Cycle must operate six times, fixing six molecules of carbon dioxide.

In essence, the Calvin Cycle is a metabolic pathway that transforms carbon dioxide and other compounds into glucose, providing energy and structural integrity to plants. This intricate process underscores the importance of both light-dependent and light-independent reactions in sustaining life on Earth.

Order and kinetics of Photosynthesis

Photosynthesis, a fundamental biological process, is an intricate sequence of events that culminates in the conversion of light energy into chemical energy in the form of glucose. Understanding the order and kinetics of photosynthesis is crucial to unraveling the mechanisms that drive this essential phenomenon. This informative discourse provides insight into the sequential stages and time scales involved in the photosynthetic process, as outlined below.

Stage 1: Energy Transfer in Antenna Chlorophyll (Thylakoid Membranes)

The inception of photosynthesis begins with the absorption of light energy by chlorophyll and other pigments located in the antenna complex of thylakoid membranes. This critical step occurs with astonishing rapidity, unfolding on the femtosecond to picosecond timescale. During this minuscule time frame, the excited electrons within the chlorophyll molecules undergo rapid energy transfer, initiating the photosynthetic cascade.

Stage 2: Transfer of Electrons in Photochemical Reactions (Thylakoid Membranes)

Following energy absorption, the second stage encompasses the transfer of these energized electrons through a series of photochemical reactions within the thylakoid membranes. This process operates at a slightly longer timescale, ranging from picoseconds to nanoseconds. As electrons shuttle through protein complexes, such as Photosystem II and Photosystem I , they undergo redox reactions that ultimately result in the generation of ATP and the reduction of NADP+ to NADPH.

Stage 3: Electron Transport Chain and ATP Synthesis (Thylakoid Membranes)

The third phase of photosynthesis involves the electron transport chain, which propels electrons through a series of membrane-bound protein complexes. This intricate molecular machinery operates on a timescale spanning from microseconds to milliseconds. As electrons flow through the transport chain, protons are pumped across the thylakoid membrane, establishing a proton gradient that fuels the synthesis of ATP via chemiosmotic coupling. This stage is pivotal in harnessing the energy from light and converting it into a biologically useful form.

Stage 4: Carbon Fixation and Export of Stable Products

The culmination of photosynthesis transpires in the fourth stage, where the acquired ATP and NADPH molecules, along with carbon dioxide, are utilized for the fixation of carbon into organic compounds. This final, but no less intricate, phase operates on a timescale ranging from milliseconds to seconds. The Calvin-Benson cycle, a series of enzyme-catalyzed reactions, assimilates carbon dioxide and generates sugars, primarily glucose, which serve as the ultimate product of photosynthesis. These stable products are subsequently exported to various parts of the plant for energy storage and growth.

In conclusion, the order and kinetics of photosynthesis encompass a meticulously orchestrated sequence of events, spanning a wide range of time scales from femtoseconds to seconds. This process showcases the remarkable efficiency of nature in harnessing light energy to sustain life on Earth, underlining its significance in the realm of biological science.

Carbon Concentrating Mechanisms in Photosynthesis

In the realm of photosynthesis, carbon concentrating mechanisms (CCMs) play a pivotal role in optimizing the carbon fixation process, especially in environments with fluctuating carbon dioxide (CO2) levels. These mechanisms are primarily observed in certain angiosperm families and are categorized based on their operational strategies.

1. C4 Photosynthesis: The C4 pathway, also known as the Hatch and Slack cycle, is a specialized mechanism observed in approximately 4% of angiosperm families, notably Poaceae and Cyperaceae. It was elucidated by scientists Hatch and Slack, who studied its manifestation in maize plants.

• Mechanism: In C4 plants, photosynthesis is spatially separated into two cell types: mesophyll cells and bundle sheath cells. The initial CO2 fixation occurs in the mesophyll cells, where CO2 is combined with phosphoenolpyruvate (PEP) by the enzyme PEP carboxylase, producing a four-carbon compound, oxaloacetic acid or malate. This compound is then transported to the bundle sheath cells, where it undergoes decarboxylation, releasing CO2. This CO2 is subsequently fixed into glucose through the conventional C3 cycle.
• Significance: The C4 mechanism is an adaptive strategy for plants in semi-arid regions. Under high temperatures and light conditions, these plants can efficiently fix CO2, even when stomata are partially closed to minimize water loss. This spatial separation reduces the oxygenase activity of RuBisCo, thereby decreasing photorespiration and enhancing carbon fixation.

2. CAM Photosynthesis: Crassulacean Acid Metabolism (CAM) is another carbon concentrating mechanism predominantly found in xerophytes like cacti and succulents, with around 16,000 species employing this strategy.

• Mechanism: Unlike C4 plants that exhibit spatial separation, CAM plants demonstrate a temporal separation of CO2 uptake and fixation. During the night, when the stomata are open, CO2 is fixed into malate by PEP carboxylase. During the day, when the stomata are closed, malate is decarboxylated to release CO2, which is then fixed through the C3 cycle.
• Significance: This mechanism allows CAM plants to efficiently conduct photosynthesis under water-limited conditions, as they can take up CO2 during cooler nights and minimize water loss during the day.

Aquatic Adaptations: In aquatic environments, cyanobacteria exhibit a unique carbon concentrating mechanism. They possess specialized structures called carboxysomes, which enrich the CO2 concentration around the RuBisCo enzyme. The enzyme carbonic anhydrase within these carboxysomes can release CO2 from dissolved bicarbonate ions, ensuring efficient carbon fixation.

In summary, carbon concentrating mechanisms are adaptive strategies that enhance the efficiency of photosynthesis under varying environmental conditions. Whether through spatial or temporal separation, or specialized cellular structures, these mechanisms ensure optimal carbon fixation, catering to the diverse needs of plants across different habitats.

Regulation of the cycle

Photosynthesis is not possible in the night, however, glycolysis, a process that utilizes the same reactions as those in the Calvin-Benson cycles, with the exception of the reverse, takes place. This means that certain steps in the cycle would be inefficient when they are allowed to take place in darkness, as they could impede the process of glycolysis. In this regard, certain enzymes in the Calvin-Benson cycle can be “turned off” (i.e. they become inactive) in darkness.

In the absence of sunlight, changes in physiological conditions often require adjustments to the rate of reaction in the Calvin-Benson cycle such that enzymes that are involved in some reactions alter their catalytic activities. These changes in enzyme activity are typically caused through changes in the levels of chloroplast components such as reduced ferredoxin and acids and the soluble components (e.g., Pi and magnesium ions).

Products of Photosynthesis

Photosynthesis, the fundamental process by which plants convert light energy into chemical energy, yields a variety of essential products that sustain life on Earth. These products can be categorized based on the specific reactions involved:

• ATP (Adenosine Triphosphate) : A primary energy currency of cells, facilitating energy transfer for various cellular processes.
• NADPH (Nicotinamide Adenine Dinucleotide Phosphate) : A coenzyme that carries electrons, crucial for the synthesis of organic molecules.
• Oxygen (O2) : Released into the atmosphere as a byproduct when water molecules are split.
• Protons (H+ ions) : These play a role in creating a proton gradient across the thylakoid membrane, driving ATP synthesis.
• Glyceraldehyde-3-Phosphate (G3P) : A three-carbon sugar molecule, which is a precursor to glucose and other carbohydrates.
• Protons (H+ ions) : Involved in the reduction of 3-phosphoglycerate to G3P.
• Glucose ( Carbohydrates ) : The primary energy storage molecule, which can be further converted into other organic compounds or used for energy by organisms.
• Water (H2O) : Some water molecules are produced during the Calvin cycle.
• Oxygen (O2) : A vital byproduct released into the atmosphere, supporting aerobic respiration in organisms.
• Sulfur : Specifically produced in photosynthetic sulfur bacteria, contributing to the sulfur cycle in ecosystems.

These products, especially glucose and oxygen, are fundamental to the survival and growth of most organisms on Earth.

Process of Photosynthesis – Overview

Photosynthesis, a vital physiological process, transpires within specialized cellular structures termed chloroplasts. These organelles house chlorophyll, the green pigment responsible for the characteristic hue of plant leaves. The leaf’s lamina facilitates the absorption of both sunlight and carbon dioxide, essential components for photosynthesis.

This intricate process can be delineated into two primary phases based on light dependency:

• Temporal Occurrence : As the name suggests, these reactions are contingent upon sunlight and predominantly occur during daylight hours.
• Location : The thylakoid membrane, within the chloroplast, is the site for these reactions.
• Grana : Situated inside the thylakoid, grana are sac-like structures that capture and store light.
• Photosystem-I (PS-I)
• Photosystem-II (PS-II)
• Electron Excitation : Upon photon absorption by chlorophyll within the reaction center, an electron is excited and subsequently released.
• Energy Conversion : This phase culminates in the conversion of solar energy into chemical energy, yielding ATP and NADPH.
• Chemical Representation : 2H2O + 2NADP+ + 3 ADP + 3Pi → O2 + 2NADPH + 3ATP
• Alternative Names : Often referred to as the dark reaction or carbon fixation.
• Location : These reactions transpire within the stroma of the chloroplast.
• Carbon Dioxide Uptake : Plants assimilate carbon dioxide via stomata, initiating the Calvin cycle.
• Sugar Formation : Through the Calvin cycle, six carbon dioxide molecules are utilized to synthesize a single sugar molecule.
• Chemical Representation : 3CO2 + 6 NADPH + 5H2O + 9ATP → G3P + 2H+ + 6NADP+ + 9ADP + 8Pi

Light-dependent reactions vs. light-independent reactions

Photosynthesis, the process by which plants convert light energy into chemical energy, is delineated into two primary phases: the light-dependent reactions and the light-independent reactions. Each phase plays a distinct role in the overall process, and they are characterized by their dependency on light and their respective locations within the chloroplast.

1. Light-Dependent Reactions:

• Location: These reactions transpire in the thylakoid membrane of the chloroplast.
• Dependency on Light: As the name suggests, light-dependent reactions necessitate the direct absorption of sunlight.
• Mechanism: Within the thylakoid membrane, chlorophyll and other pigments absorb photons from sunlight. This absorption triggers a series of electron transport chains, leading to the synthesis of energy-rich molecules, adenosine triphosphate ( ATP ) and nicotinamide adenine dinucleotide phosphate (NADPH).
• Outcome: The primary products of light-dependent reactions are ATP and NADPH, which store the energy harnessed from sunlight in chemical form.

2. Light-Independent Reactions (Calvin Cycle):

• Location: These reactions occur in the stroma, the fluid-filled space between the thylakoid membranes and the chloroplast envelope.
• Dependency on Light: Contrary to light-dependent reactions, the Calvin Cycle operates independently of direct light exposure, hence the designation “light-independent.”
• Mechanism: Utilizing the energy stored in ATP and NADPH, the Calvin Cycle facilitates the fixation of atmospheric carbon dioxide (CO2) into organic molecules. Through a series of enzymatic reactions, CO2 is converted into carbohydrate molecules, such as glucose.
• Outcome: The culmination of the Calvin Cycle is the synthesis of glucose and other carbohydrates, which serve as energy reservoirs for the plant and are crucial for growth and development.

Photosynthesis examples

Photosynthesis, the process by which organisms convert light energy into chemical energy, manifests in various forms across different species. Here are specific examples:

• Organisms : Green plants and oxygenic bacteria, notably cyanobacteria.
• Pigment Involved : Chlorophyll, a green pigment, plays a pivotal role in capturing light energy.
• Location : This process occurs within the thylakoids of chloroplasts.
• Reactants : Carbon dioxide and water.
• Products : Oxygen gas, glucose, and water molecules. In plants, glucose units are often linked to form compounds like starch, fructose, or sucrose.
• Organisms : Purple sulfur bacteria and green sulfur bacteria.
• Pigment Involved : While green sulfur bacteria utilize chlorophyll, purple sulfur bacteria predominantly use carotenoids as their photosynthetic pigments.
• Location : Within specialized structures in bacterial cells.
• Reactants : Carbon dioxide and hydrogen sulfide (H2S) serve as the primary reactants, replacing water.
• Products : Carbohydrates (which may not always be glucose), sulfur gas, and water molecules.
• Organisms : Red algae (Rhodophyta).
• Pigment Involved : Phycobiliproteins, especially phycoerythrin, give red algae its distinctive color and play a role in capturing light energy.
• Location : Within the chloroplasts of red algae cells.
• Products : Oxygen gas and carbohydrates. Red algae often produce floridean starch as their primary carbohydrate storage molecule.
• Organisms : Diatoms , a major group of microalgae found in oceans, waterways, and soils.
• Pigment Involved : Chlorophyll-a and chlorophyll-c, along with fucoxanthin, a brown pigment that gives diatoms their golden-brown color.
• Location : Within the chloroplasts of diatom cells, which are often encased in intricate silica shells.
• Products : Oxygen gas and carbohydrates. Diatoms store energy primarily as chrysolaminarin, a water-soluble polysaccharide.

These examples underscore the diversity of photosynthetic processes across different organisms, each adapted to their unique environments and energy requirements.

Importance of photosynthesis

• Photosynthesis serves as the fundamental energy conversion mechanism for autotrophic organisms. Through this process, they harness solar energy, converting it into chemical energy stored in the form of glucose and other carbohydrates. This self-sustenance allows them to thrive in diverse ecosystems.
• Autotrophs , primarily plants and certain bacteria, form the base of the food chain. Heterotrophic organisms, including animals and humans, rely on these primary producers for their energy and nutritional needs. Without photosynthesis, the foundation of this chain would collapse, disrupting the balance of ecosystems.
• Photosynthesis is a critical contributor to the planet’s oxygen levels. As plants and photosynthetic bacteria convert carbon dioxide into glucose, they release oxygen as a byproduct. This oxygen replenishes the atmosphere, ensuring its availability for aerobic respiration in various organisms.
• Through photosynthesis, plants play a pivotal role in the global carbon cycle. They absorb atmospheric carbon dioxide, converting it into organic compounds. This process aids in mitigating the effects of excessive carbon dioxide, which is a major greenhouse gas contributing to global warming.
• Photosynthesis facilitates various symbiotic relationships in nature. For instance, plants provide oxygen and nutrients to animals, which in turn produce carbon dioxide and other organic matter that plants utilize. This mutualistic relationship underscores the interconnectedness of life.
• The sun is the ultimate energy source for Earth. Through photosynthesis, this radiant energy is captured and transformed into a form that can be used by a myriad of organisms. This process underscores the significance of solar energy in sustaining life on the planet.

In essence, photosynthesis is not just a biological process but a cornerstone of life on Earth. It interlinks various biogeochemical cycles, supports biodiversity, and ensures the continuity of energy flow in ecosystems.

What is Artificial photosynthesis?

• Artificial photosynthesis refers to a chemically engineered process that emulates the natural mechanism by which plants, algae, and certain bacteria harness sunlight to convert water and carbon dioxide into oxygen and energy-rich carbohydrates.
• Central to artificial photosynthesis is the use of photocatalysts. These are specialized compounds designed to facilitate the oxidation-reduction reactions analogous to those in natural photosynthesis. Their role is pivotal in capturing and converting solar energy efficiently.
• The primary aim of artificial photosynthesis is the generation of solar fuels. These are energy carriers synthesized directly from sunlight, allowing for energy storage and utilization even in the absence of direct sunlight.
• One of the significant outcomes of artificial photosynthesis is the production of oxygen from water and sunlight. This process offers a sustainable and environmentally friendly approach to energy generation, minimizing carbon emissions and other pollutants.
• A crucial component of artificial photosynthesis is the photocatalytic division of water molecules. This process yields oxygen and a substantial volume of hydrogen gas, a potential clean fuel source with myriad applications.
• Beyond water splitting, artificial photosynthesis can also drive carbon reduction, mirroring the natural carbon fixation pathway. This results in the synthesis of carbohydrate molecules, providing another avenue for energy storage.
• The implications of artificial photosynthesis are vast. It holds promise in diverse fields such as photoelectrochemistry, enzyme engineering, and the development of photoautotrophic microorganisms. These applications can lead to the production of microbial biofuels and biohydrogen, offering sustainable energy solutions derived directly from sunlight.

Photosynthesis vs Cellular respiration

Photosynthesis and cellular respiration are two fundamental biochemical processes that sustain life on Earth. While they are interconnected and interdependent, they serve distinct roles in the energy dynamics of living organisms. Here, we elucidate the key differences between these two processes:

• Type : An anabolic process, which means it involves the synthesis of complex molecules from simpler ones.
• Energy Dynamics : Endergonic and endothermic, signifying that it absorbs energy.
• Type : A catabolic process, implying the breakdown of complex molecules to release energy.
• Energy Dynamics : Exergonic and exothermic, indicating that it releases energy.
• Photosynthesis : Takes place in the chloroplasts of eukaryotic phototrophic cells, specifically within the thylakoids.
• Cellular Respiration : Primarily occurs in the mitochondria of cells.
• Reactants : Carbon dioxide, water, and light energy.
• Products : Glucose (a carbohydrate), oxygen, and in some instances, water.
• Reactants : Glucose and oxygen.
• Products : Carbon dioxide, water, and energy in the form of adenosine triphosphate ( ATP ).
• Photosynthesis : 6CO2 + 6H2O (in the presence of light energy) → C6H12O6 + 6O2
• Cellular Respiration : C6H12O6 + 6O2 → 6CO2 + 6H2O
• Photosynthesis : Conducted by green plants, certain algae, and some photosynthetic bacteria.
• Cellular Respiration : A universal process that occurs in all living organisms.
• Photosynthesis : Exclusively occurs in the presence of sunlight.
• Cellular Respiration : A continuous process that does not necessitate sunlight.

Evolution of Photosynthesis

The evolution of photosynthesis is a fascinating journey through Earth’s history, representing a pivotal moment in the development of life on our planet. This process has not only shaped the composition of the Earth’s atmosphere but has also played a fundamental role in the emergence of complex life forms. In this scientific exploration, we delve into the key milestones and mechanisms underlying the evolution of photosynthesis.

Early Photosynthetic Organisms:

The fossil record provides intriguing insights into the origins of photosynthesis. Fossils of filamentous photosynthetic organisms, dating back approximately 3.4 billion years, suggest that photosynthesis may have commenced around this time. These ancient organisms likely laid the foundation for the photosynthetic processes we observe today.

Oxygenic Photosynthesis Emergence:

The most significant shift in Earth’s history was the rise of oxygenic photosynthesis, which ultimately led to the oxygenation of our planet. Geological evidence points to the emergence of oxygenic photosynthesis, notably in cyanobacteria, during the Paleoproterozoic era, roughly 2 billion years ago. This marked the inception of an era often referred to as the “oxygen catastrophe,” as oxygen levels in the atmosphere began to rise significantly.

Symbiosis and Chloroplast Origins:

One intriguing aspect of photosynthesis evolution is the symbiotic relationships that have developed between photosynthetic organisms and various life forms. Notably, corals, sponges, sea anemones, and even certain mollusks, such as Elysia viridis and Elysia chlorotica, have formed symbiotic connections with photosynthetic algae. These relationships are often attributed to the simplicity of the host organisms’ body plans and their ability to maximize surface area for photosynthesis.

Endosymbiotic Theory and Chloroplasts:

A pivotal moment in the evolution of photosynthesis occurred with the origin of chloroplasts. Chloroplasts, which bear striking similarities to photosynthetic bacteria, are thought to have originated through endosymbiosis. According to this theory, early eukaryotic cells engulfed photosynthetic bacteria, eventually forming the first plant cells. The evidence for this theory lies in the presence of chloroplast DNA, separate from the host cell’s nucleus, resembling the genetic makeup of cyanobacteria. This genetic legacy supports the notion that chloroplasts evolved from photosynthetic bacteria.

Diversity of Photosynthetic Lineages:

Photosynthesis has diversified over time, resulting in various lineages of photosynthetic organisms. These include:

• Archaeplastida (uni- and multicellular): Comprising glaucophytes, red and green algae.
• Cryptista (unicellular): Encompassing cryptophytes.
• Haptista (unicellular): Represented by haptophytes.
• Alveolata (unicellular): Incorporating dinoflagellates, chromerids, and Pseudoblepharisma.
• Stramenopila (uni- and multicellular): Encompassing ochrophytes.
• Rhizaria (unicellular): Comprising chlorarachniophytes and select Paulinella species.
• Excavata (unicellular): Including euglenids.

These lineages, whether uni- or multicellular, reveal the diversification of photosynthetic organisms and their adaptive strategies.

Prokaryotic Photosynthesis:

Early photosynthetic systems, particularly those of green and purple sulfur and green and purple nonsulfur bacteria, were likely anoxygenic and utilized various molecules, such as hydrogen, sulfur, and organic acids, as electron donors. These systems were consistent with the highly reducing conditions of the early Earth’s atmosphere. Archaea , including haloarchaea, can harness energy from the sun but do not perform oxygenic photosynthesis.

In conclusion, the evolution of photosynthesis is a captivating narrative of life’s adaptation to Earth’s changing conditions. From the emergence of early photosynthetic organisms to the rise of oxygenic photosynthesis and the formation of symbiotic relationships, photosynthesis has played a pivotal role in shaping our planet’s history and continues to be a cornerstone of life as we know it. This intricate process underscores the remarkable complexity and diversity of life on Earth.

Quiz Practice

MCQ 1: What is the primary pigment responsible for capturing light energy in photosynthesis?

A) Chlorophyll B) Carotenoid C) Xanthophyll D) Phycobilin

MCQ 2: In which organelle does photosynthesis primarily occur in plant cells?

A) Nucleus B) Mitochondria C) Chloroplast D) Endoplasmic reticulum

MCQ 3: During the light-dependent reactions of photosynthesis, what molecule is produced as a byproduct?

A) Oxygen B) Carbon dioxide C) Glucose D) Water

MCQ 4: What is the primary source of carbon dioxide for photosynthesis in most plants?

A) Soil B) Air C) Water D) Other plants

MCQ 5: Which of the following colors of light is least effective in driving photosynthesis?

A) Red B) Blue C) Green D) Yellow

MCQ 6: What is the ultimate goal of the Calvin cycle in photosynthesis?

A) Produce ATP B) Convert glucose to starch C) Generate carbon dioxide D) Synthesize glucose

MCQ 7: In C4 plants, what is the primary function of mesophyll cells?

A) Storing water B) Capturing light energy C) Fixing carbon dioxide D) Producing oxygen

MCQ 8: What gas is necessary for the opening of stomata during photosynthesis?

A) Oxygen B) Carbon dioxide C) Nitrogen D) Hydrogen

MCQ 9: Which environmental factor can limit the rate of photosynthesis?

A) High oxygen levels B) Low carbon dioxide levels C) Warm temperatures D) Bright sunlight

MCQ 10: What is the primary purpose of the light-independent reactions (Calvin cycle) in photosynthesis?

A) Generate oxygen B) Produce ATP C) Fix carbon dioxide D) Capture light energy

Where does photosynthesis take place?

In plants, photosynthesis takes place in chloroplasts, which contain the chlorophyll. Chloroplasts are surrounded by a double membrane and contain a third inner membrane, called the thylakoid membrane, that forms long folds within the organelle.

What are the reactants of photosynthesis?

The process of photosynthesis is commonly written as: 6CO2 + 6H2O → C6H12O6 + 6O2. 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.

How are photosynthesis and cellular respiration related?

Photosynthesis is the process by which atmospheric carbon dioxide is assimilated and converted to glucose and oxygen is released. CO2 and H2O are utilised in the process. In the cellular respiration, glucose is broken down to CO2 and energy is released in the form of ATP , which is utilised in performing various metabolic processes. Oxygen is utilised in the process. Energy is stored in the process of photosynthesis, whereas it is released in the process of cellular respiration. The process of cellular respiration and photosynthesis complement each other. These processes help cells to release and store the energy respectively. They are required to keep the atmospheric balance of carbon dioxide and oxygen concentrations.

What is the equation for photosynthesis?

The process of photosynthesis is commonly written as: 6CO2 + 6H2O → C6H12O6 + 6O2

Where does photosynthesis occur?

chloroplasts

What are the products of photosynthesis?

Let’s look at the products of photosynthesis! During the process of photosynthesis plants break apart the reactants of carbon dioxide and water and recombine them to produce oxygen (O2) and a form of sugar called glucose (C6H12O6).

Why is photosynthesis important?

Photosynthesis is the main source of food on earth. It releases oxygen which is an important element for the survival of life. Without photosynthesis, there will be no oxygen on earth. The stored chemical energy in plants flows into herbivores, carnivores, predators, parasites, decomposers, and all life forms.

Which of these equations best summarizes photosynthesis? A. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy B. C6H12O6 + 6 O2 → 6 CO2 + 12 H2O C. 6 CO2 + 6 H2O → C6H12O6 + 6 O2 D. 6 CO2 + 6 O2 → C6H12O6 + 6 H2O E. H2O → 2 H+ + 1/2 O2 + 2e-

Ans: C. 6 CO2 + 6 H2O → C6H12O6 + 6 O2

What are the raw materials of photosynthesis?

The raw materials of photosynthesis, water and carbon dioxide, enter the cells of the leaf. Oxygen, a by-product of photosynthesis, and water vapor exit the leaf.

Which gas is removed from the atmosphere during photosynthesis?

Photosynthesis removes CO2 from the atmosphere and replaces it with O2.

Which of the following sequences correctly represents the flow of electrons during photosynthesis? A. NADPH → O2 → CO2 B. H2O → NADPH → Calvin cycle C. NADPH → chlorophyll → Calvin cycle D. H2O → photosystem I → photosystem II

The correct option is B H2O → NADPH → Calvin cycle Electrons flow from water through the photosystem II, electron transport chain, and photosystem I to NADP+. The electrons of NADPH thus formed are then used in the Calvin cycle.

What organelle does photosynthesis occur in

What are the inputs of photosynthesis.

In photosynthesis, water, carbon dioxide, and energy in the form of sunlight are inputs, and the outputs are glucose and oxygen.

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• Leegood, R. C. (2004). Photosynthesis. Encyclopedia of Biological Chemistry, 330–335. doi:10.1016/b0-12-443710-9/00487-7
• Boyer, R. (2006). Concepts in Biochemistry , 3rd edition. John Wiley & Sons.
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• Martin, W. F., Garg, S., & Zimorski, V. (2015). Endosymbiotic theories for eukaryote origin. Philosophical Transactions of the Royal Society B: Biological Sciences , 370(1678), 20140330. doi:10.1098/rstb.2014.0330
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• Gao, J., Wang, H., Yuan, Q., & Feng, Y. (2018). Structure and Function of the Photosystem Supercomplexes. Frontiers in Plant Science , 9. doi:10.3389/fpls.2018.00357
• Rutherford, A. W., & Faller, P. (2003, January). “Photosystem II: evolutionary perspectives.” Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences , 358(1429), 245–253. doi:10.1098/rstb.2002.1186. PMC 1693113. PMID 12594932.
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• Earl, H., & Said Ennahli, S. (2004). “Estimating photosynthetic electron transport via chlorophyll fluorometry without Photosystem II light saturation.” Photosynthesis Research , 82(2), 177–186. doi:10.1007/s11120-004-1454-3. PMID 16151873. S2CID 291238.

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Photosynthesis - what is photosynthesis?

Photosynthesis enables plants and algae to convert CO2 and water into vital oxygen and sugar. This is why scientists are also working with photosynthesis in the battle against climate change and food shortages.

What is photosynthesis?

When Earth formed from a cloud of gas and dust around the young Sun approximately 4.6 billion years ago, our planet's atmosphere contained no oxygen.

About one billion years later, tiny blue-green bacteria emerged in the oceans and began to produce oxygen. They triggered the development of Earth's oxygen-rich atmosphere, which forms the basis for not only humans, but all animals on the planet to breathe.

Oxygen is produced through photosynthesis.

Photosynthesis is a biochemical process that enables plants, algae, and some bacteria to absorb the inorganic substances of carbon dioxide (CO2) and water (H20) to form the carbohydrate of glucose, which enables plants to grow.

Just as importantly, oxygen is produced as a waste product of the process, making photosynthesis the most important biochemical process on Earth.

The formula for photosynthesis is:

6 CO2 + 6 H2O + light energy --> C6H12O6 (glucose) + 6 O2

How does photosynthesis work?

Green plants use energy from light through photosynthesis. The process converts the CO2 of the air into oxygen and carbon compounds (sugars).

How photosynthesis works

Photosynthesis is a process in which plants use microscopic chloroplasts in leaves to capture the energy of light and utilise it to convert water and carbon dioxide into sugar and oxygen.

Water (H2O) is carried from the plant's roots to the leaves.

Light energy from the Sun splits the water molecules, releasing electrons.

Photosynthesis takes place in the chloroplasts of plant cells.

Carbon dioxide (CO2) is absorbed through stomata in plant cells.

Carbon (C), a building block of the plant, is formed, when electrons released from water split carbon dioxide (CO2).

Oxygen (O2) is released by the plant as a waste product of the process.

When was photosynthesis discovered?

In other words, plants work in the opposite way of humans and animals, which inhale oxygen and exhale CO2 - also known as respiration.

This was discovered by Dutch scientist Jan Ingenhousz in 1771. He documented that plants release oxygen bubbles when exposed to sunlight and release carbon dioxide when it gets dark.

In 1999, Greenlandic researcher Minik Rosing sensationally found evidence of photosynthesis in Greenlandic rock. The evidence came in the shape of carbon deposited by cyanobacteria, also known as blue-green algae, 3.7 billion years ago.

Photosynthesis is undoubtedly the most dramatic thing that has happened to life on Earth. Minik Rosing, Professor of Geology at the University of Copenhagen

Like plants, cyanobacteria convert sunlight into chemical energy and produce oxygen as a waste product. All the oxygen the bacteria produced in the oceans through photosynthesis over the next hundreds of millions of years provided a breeding ground for new and more sophisticated life forms.

Cyanobacteria have existed for 3+ billion years, and their oxygenic photosynthesis forms the basis of all life on Earth as we know it.

In the course of several geological periods, cyanobacteria pumped oxygen into the environment. Initially, the oxygen was chemically bound by substances such as iron, so it did not end up in the atmosphere.

Over time, however, the oxygen from photosynthesis filled the atmosphere. In addition, the ozone layer, which protects life from the Sun's ultraviolet radiation, was formed.

For the past two billion years, Earth has had an oxygen-rich atmosphere, and calculations show that today, 280 billion t of oxygen are produced on Earth every year. 46 % of the oxygen are produced in the oceans by algae and cyanobacteria, while the remaining 54 % are produced on dry land.

This corresponds to 21 % of the atmosphere (the rest of the atmosphere is made up of nitrogen, CO2, and other gases). 46 % of the oxygen are produced in the oceans by algae and cyanobacteria, while the remaining 54 % are produced on dry land.

Video: NASA observes photosynthesis from space

Hundreds of km from Earth's surface, satellites detect the invisible light - fluorescent light - that plants emit during photosynthesis.

Climate change and photosynthesis

For millions of years, the ratio of oxygen to CO2 was in natural balance in the atmosphere, but over the past few decades, the balance has been disturbed.

In 2019, global atmospheric CO2 emissions reached 37 gigatonnes, which is 30 % higher than in the 1970s.

Scientists widely agree that the increase in CO2 emissions is due to the burning of fossil fuels, which explains why natural photosynthesis cannot keep up - and why CO2 levels in the atmosphere are steadily increasing.

Therefore, research is also being done to find new ways to store or capture CO2, so that the concentration in the atmosphere does not continue to skyrocket.

Artificial leaves perform photosynthesis

Artificial leaves that mimic nature's photosynthesis have been invented several times.

Unfortunately, they have all shared the same problem. The leaves can convert CO2 from pressurised tanks in a lab, but they cannot extract CO2 from ordinary atmospheric air. Until now.

In 2019, researchers developed a special membrane that can solve the problem.

The membrane encapsulates the artificial leaf and bathes it in water while it performs photosynthesis. When the sunlight heats the water behind the membrane, it can evaporate through the subsurface of the leaf and absorb CO2 through small slots on the surface of the leaf. The slots are similar to the stomata of natural leaves.

A light-absorbing material captures energy from sunlight, which, together with a number of auxiliary substances, triggers photosynthesis in the artificial leaf.

The artificial leaf converts CO2 into oxygen and carbon monoxide (CO). The oxygen can be captured or released, while the carbon monoxide can be used in synthetic fuel.

How artificial leaf photosynthesis works

Scientists have invented a membrane that envelops artificial leaves in water, enabling the leaves to draw CO2 from the air and hence provide themselves with the raw material for photosynthesis.

Sea slug harvests chloroplasts

The Elysia chlorotica sea slug sucks chloroplasts out of the algae with a straw-like structure, absorbing them into its cells, so it can convert sunlight into energy.

Pea aphids produce pigments

The pea aphid (Acyrthosiphon pisum) produces plant pigments that likely enable the insect to harvest energy from sunlight.

Salamanders parasitise on algae

The spotted salamander (Ambystoma maculatum) is colonised by algae in the embryonic stage, when the egg grows in water. The embryo hoards oxygen and glucose from the algae, as they perform photosynthesis.

Researchers hack photosynthesis

In 2019, a new international research project known as Realizing Increased Photosynthetic Efficiency (RIPE) succeeded in genetically modifying the leaves of tobacco plants to make them much more efficient at photosynthesis.

When plants capture carbon dioxide from the air, they do so via the rubisco enzyme. Unfortunately, the enzyme not only captures carbon dioxide, but also oxygen, producing toxins that the plant requires energy to break down.

This detoxification process means the plant has less energy to convert the CO2 into glucose, which fuels the plant's growth.

The researchers' genetically modified leaves made detoxification in tobacco plants much more efficient, causing the plants to grow faster and up to 40% larger compared to normal tobacco plants.

The next step is to test the method on tomatoes, soybeans, and similar plants, so that plant-based food production can double over the next 50 years, which is necessary to feed a world population expected to hit nine billion by then.

• Biology Article
• What is Photosynthesis

What Is Photosynthesis?

“Photosynthesis is the process used by green plants and a few organisms that use sunlight, carbon dioxide and water to prepare their food.”

The process of photosynthesis is used by plants, algae and certain bacteria that convert light energy into chemical energy. The glucose formed during the process of photosynthesis provides two important resources to organisms: energy and fixed carbon.

Read on to explore what is photosynthesis and the processes associated with it.

Site of Photosynthesis

Photosynthesis takes place in special organelles known as chloroplast. This organelle has its own DNA, genes and hence can synthesize its own proteins. Chloroplasts consist of stroma, fluid, and stack of thylakoids known as grana. There are three important pigments present in the chloroplast that absorb light energy, chlorophyll a, chlorophyll b, and carotenoids.

Also Read: Photosynthesis Process

Types of Photosynthesis

There are two different types of photosynthesis:

• Oxygenic photosynthesis
• Anoxygenic photosynthesis

Oxygenic Photosynthesis

Oxygenic photosynthesis is more common in plants, algae and cyanobacteria. During this process, electrons are transferred from water to carbon dioxide by light energy, to produce energy. During this transfer of electrons, carbon dioxide is reduced while water is oxidized, and oxygen is produced along with carbohydrates.

During this process, plants take in carbon dioxide and expel oxygen into the atmosphere.

This process can be represented by the equation:

6CO2+ 12H2O + LIGHT ENERGY → C6H12O6 + 6O2 + 6H2O

Anoxygenic Photosynthesis

This type of photosynthesis is usually seen in certain bacteria, such as green sulphur bacteria and purple bacteria which dwell in various aquatic habitats. Oxygen is not produced during the process.

The anoxygenic photosynthesis can be represented by the equation:

CO2 + 2H2A + LIGHT ENERGY → [CH2O] + 2A + H2O

Also Read:  Difference between Photosynthesis and Respiration

Photosynthesis Apparatus

The photosynthesis apparatus includes the following essential components:

Pigments not only provide colour to the photosynthetic organisms, but are also responsible for trapping sunlight. The important pigments associated with photosynthesis include:

• Chlorophyll: It is a green-coloured pigment that traps blue and red light. Chlorophyll is subdivided into, “chlorophyll a”, “chlorophyll b”, and “chlorophyll c”. “Chlorophyll a” is widely present in all the photosynthetic cells. A bacterial variant of chlorophyll known as bacteriochlorophyll can absorb infrared rays .
• Carotenoids: These are yellow, orange or red-coloured pigments that absorb bluish-green light. Xanthophyll and carotenes are examples of carotenoids.
• Phycobilins: These are present in bacteria and red algae . These are red and blue pigments that absorb wavelength of light that are not properly absorbed by carotenoids and chlorophyll.

Plastids are organelles found in the cytoplasm of eukaryotic photosynthetic organisms. They contain pigments and can also store nutrients. Plastids are of three types:

• Leucoplast: These are colourless, non-pigmented and can store fats and starch.
• Chromoplasts: They contain carotenoids.
• Chloroplasts: These contain chlorophyll and are the site of photosynthesis.

Antennae is the collection of 100 to 5000 pigment molecules that capture light energy from the sun in the form of photons. The light energy is transferred to a pigment-protein complex that converts light energy to chemical energy.

Reaction Centers

The pigment-protein complex responsible for the conversion of light energy to chemical energy forms the reaction centre.

Also Read: Photosynthesis

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photosynthesis

Definition of photosynthesis

Did you know.

Photosynthesis Has Greek Roots

The Greek roots of photosynthesis combine to produce the basic meaning "to put together with the help of light". Photosynthesis is what first produced oxygen in the atmosphere billions of years ago, and it's still what keeps it there. Sunlight splits the water molecules (made of hydrogen and oxygen) held in a plant's leaves and releases the oxygen in them into the air. The leftover hydrogen combines with carbon dioxide to produce carbohydrates, which the plant uses as food—as do any animals or humans who might eat the plant.

Examples of photosynthesis in a Sentence

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'photosynthesis.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

1898, in the meaning defined above

Dictionary Entries Near photosynthesis

photosynthate

photosynthetic ratio

Cite this Entry

“Photosynthesis.” Merriam-Webster.com Dictionary , Merriam-Webster, https://www.merriam-webster.com/dictionary/photosynthesis. Accessed 8 May. 2024.

Kids Definition

Kids definition of photosynthesis, medical definition, medical definition of photosynthesis, more from merriam-webster on photosynthesis.

Nglish: Translation of photosynthesis for Spanish Speakers

Britannica.com: Encyclopedia article about photosynthesis

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Photosynthesis – Photolysis and Carbon Fixation

The process of photosynthesis

Table of Contents

Photosynthesis is the means that primary producers (mostly plants) can obtain energy via light energy. The energy gained FROM light can be used in various processes mentioned below for the creation of energy that the plant will need to survive and grow.

Photosynthesis is a reduction process, where hydrogen is reduced by a coenzyme. This is in contrast to respiration where glucose is oxidized.

The process is split INTO two DISTINCT areas,  photolysis  (the photochemical stage) and the  Calvin Cycle  (the thermochemical stage). The diagram below gives a summary of the reaction, where light energy is used to initiate the reaction in its presence;

CO 2  + H 2 O > glucose + oxygen

This part of photosynthesis occurs in the  granum  of  a   chloroplast  where light is absorbed by  chlorophyll ; a type of photosynthetic pigment that converts the light to chemical energy. This reacts with water (H 2 O) and splits the oxygen and hydrogen molecules apart.

From this dissection of water, the oxygen is released as a by-product while the reduced hydrogen acceptor makes its way to the second stage of photosynthesis, the Calvin cycle.

Overall, since the water is oxidized (hydrogen is removed) and energy is gained in photolysis which is required in the Calvin cycle

The Calvin Cycle

Also known as the carbon fixation stage, this part of the photosynthetic process occurs in the  stroma  of chloroplasts. The carbon made available FROM breathing in carbon dioxide enters this cycle, which is illustrated below:

Just like the  Kreb’s Cycle  in respiration, a substrate is manipulated INTO various carbon compounds to produce energy. In the case of photosynthesis, the following steps occur, which create glucose for respiration FROM the carbon dioxide introduced INTO the cycle;

• Carbon FROM CO 2  enters the cycle combining with Ribulose Biphosphate (RuBP)
• A compound formed is unstable and breaks down FROM its 6 carbon nature to a 3 carbon compound called glycerate phosphate (GP)
• Energy is used to break down GP INTO triose phosphate, while a hydrogen acceptor reduces the compound, therefore, requiring energy
• Triose Phosphate is the end product of this, a 3 carbon compound which can double up to form glucose, which can be used in respiration.
• The cycle is completed when the leftover GP molecules are met with a carbon acceptor and then turned INTO RuBP, which is to be joined with the carbon dioxide molecules to re-begin the process.

The energy that is used up in the Calvin cycle is the energy that is made available during photolysis. The glucose that is made via GP can be used in respiration or a building block in forming  starch  and  cellulose , materials that are commonly in demand in plants.

Limiting Factors in Photosynthesis

Some factors affect the rate of photosynthesis in plants, as follows

• Temperature  plays a role in affecting the rate of photosynthesis. Enzymes involved in the photosynthetic process are directly affected by the temperature of the organism and its environment
• Light Intensity is also a  limiting factor , if there is no sunlight, then the photolysis of water cannot occur without the light energy required.
• Carbon Dioxide concentration also plays a factor, due to the supplies of carbon dioxide required in the Calvin cycle stage.

Overall, this is how a plant produces energy which supplies a rich source of glucose for respiration and the building blocks for more complex materials. While animals get their energy FROM food, plants get their energy FROM the sun.

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What is photosynthesis?

April 28, 2020 By Emma Vanstone Leave a Comment

Green plants make sugar for growth by a process called photosynthesis . Photosynthesis is a process where light energy is converted to chemical energy in the form of sugars. It’s a process that provides the main source of oxygen in the atmosphere and is essential for almost all life on Earth.

Photosynthesis made simple

Plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of glucose.

The glucose molecules created by photosynthesis act as fuel for cells and are used for cellular respiration and fermentation.

Photosynthesis Equation

Carbon dioxide + water  (and light ) ———> glucose and oxygen

Where does photosynthesis happen?

Photosynthesis takes place in chloroplast cells, which contain a substance called chlorophyll. It is chlorophyll, which gives plants their green colour.

Chloroplasts are one of the organelles in a plant cell. We made a jelly model of plant cell to learn about organelles and plant cell structure.

Sunlight is also needed to make chlorophyll. If plants are kept in the dark, they can’t make chlorophyll and will have yellow leaves! You can see this in our multicoloured cress caterpillar .

What affects the rate of photosynthesis

Four factors affect the rate of photosynthesis . The faster it occurs, the more the plant grows.

Light  – the more light there is, the faster photosynthesis occurs.

Water  – lack of water slows photosynthesis down.

Temperature  – photosynthesis works best at around 30 degrees Celsius.

Carbon dioxide levels  – photosynthesis is faster if there is more carbon dioxide in the air.

Plants make the energy to grow through a process called respiration . This uses the sugar produced by photosynthesis and oxygen.

How are leaves adapted for photosynthesis?

Leaves are green as they contain lots of chlorophyll, which absorbs sunlight.

They are thin and have a large surface area. This means they can absorb a lot of sunlight, and gases such as oxygen and carbon dioxide can pass in and out of the leaf easily.

Leaves have veins – xylem and phloem, which transport water, minerals and sugars around the plant.

Do only plants photosynthesise?

Plants, algae, and some types of bacteria use photosynthesis to create energy.

A large percentage of the Earth’s oxygen comes from phytoplankton in the oceans, which contain chlorophyll and use photosynthesis to create energy.

What is chlorophyll?

Chlorophyll is a green pigment which absorbs energy from blue and red light waves and reflects green light waves, which is why plants look green!

Chlorophyll in a plant is found in an organelle called a chloroplast. This is where photosynthesis occurs.

Why is photosynthesis important?

Photosynthesis also allows plants to make energy for growth and repair, and it has an important ecological impact.

Plants incorporate the carbon from carbon dioxide into organic molecules ( carbon fixation ). This creates a carbon source for animals who cannot create their own and also removes carbon dioxide from the air, slowing down the rate at which it builds up in the atmosphere.

Photosynthesis also creates oxygen, which is needed for most life on Earth!

Do you have more questions? You might find the answers in my collection of science questions for kids .

Last Updated on January 26, 2024 by Emma Vanstone

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photosynthesis

[ foh-t uh - sin -th uh -sis ]

• the complex process by which carbon dioxide, water, and certain inorganic salts are converted into carbohydrates by green plants, algae, and certain bacteria, using energy from the sun and chlorophyll .

/ ˌfəʊtəʊsɪnˈθɛtɪk; ˌfəʊtəʊˈsɪnθɪsɪs /

• (in plants) the synthesis of organic compounds from carbon dioxide and water (with the release of oxygen) using light energy absorbed by chlorophyll
• the corresponding process in certain bacteria

/ fō′tō-sĭn ′ thĭ-sĭs /

• The process by which green plants, algae, diatoms, and certain forms of bacteria make carbohydrates from carbon dioxide and water in the presence of chlorophyll, using energy captured from sunlight by chlorophyll, and releasing excess oxygen as a byproduct. In plants and algae, photosynthesis takes place in organelles called chloroplasts . Photosynthesis is usually viewed as a two-step process. First, in the light reactions , the energy-providing molecule ATP is synthesized using light energy absorbed by chlorophyll and accessory pigments such as carotenoids and phycobilins, and water is broken apart into oxygen and a hydrogen ion, with the electron of the hydrogen transferred to another energy molecule, NADPH. The ATP and NADPH molecules power the second part of photosynthesis by the transfer of electrons. In these light-independent or dark reactions , carbon is broken away from carbon dioxide and combined with hydrogen via the Calvin cycle to create carbohydrates. Some of the carbohydrates, the sugars, can then be transported around the organism for immediate use; others, the starches, can be stored for later use.
• Compare chemosynthesis See Note at transpiration
• Use by green plants of the energy in sunlight to carry out chemical reactions , such as the conversion of carbon dioxide into oxygen . Photosynthesis also produces the sugars that feed the plant.

Discover More

Derived forms.

• ˌphotosynˈthetically , adverb
• photosynthetic , adjective

Other Words From

• pho·to·syn·thet·ic [ foh-t, uh, -sin-, thet, -ik ] , adjective
• photo·syn·theti·cal·ly adverb
• non·photo·syn·thetic adjective

Word History and Origins

Origin of photosynthesis 1

A Closer Look

Compare meanings.

How does photosynthesis compare to similar and commonly confused words? Explore the most common comparisons:

• chemosynthesis vs. photosynthesis
• photosynthesis vs. cellular respiration
• photorespiration vs. photosynthesis

Example Sentences

Specifically, he was interested in the protein-based "reaction centers" in spinach leaves that are the basic mechanism for photosynthesis—the chemical process by which plants convert carbon dioxide into oxygen and carbohydrates.

Algae and plants use photosynthesis to turn sunlight into food.

According to the Washington Post, this happens because as the days shorten and turn frigid, it’s not worth it for some trees to expend energy to conduct photosynthesis.

In a steady state, most of the energy captured by photosynthesis is used up by the furnace of respiration and metabolism burning on Earth’s surface by its infrared layer of life.

There’s no sunlight beneath half a mile of ice, so of course there’s no photosynthesis.

Nevertheless, it was required, and at least it was more fun than studying algebra or photosynthesis.

Re-solarizing the food chain should be our goal in every way—taking advantage of the everyday miracle that is photosynthesis.

As the microbes moved toward the light to carry out photosynthesis, they projected the image of the stencil.

Timiriazeff, in his Croonian Lecture, was the first to see the connexion between photosynthesis and the Lagado research.

On the other hand, their ancestors, the green or yellow mastigota, form new plasm by photosynthesis like true cells.

There the miracle of life consists merely of the chemical process of plasmodomism by photosynthesis.

Like von Baeyer's hypothesis, this assumes that formaldehyde and oxygen are the first products of photosynthesis.

In general, starch is the final product of photosynthesis in most green plants; but there are many exceptions to this.