photosynthesis short note

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Development of the idea

Overall reaction of photosynthesis.

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

Why is photosynthesis important?

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

photosynthesis

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• Khan Academy - Photosynthesis
• Biology LibreTexts - Photosynthesis
• University of Florida - Institute of Food and Agricultural Sciences - Photosynthesis
• Milne Library - Inanimate Life - Photosynthesis
• National Center for Biotechnology Information - Chloroplasts and Photosynthesis
• Roger Williams University Pressbooks - Introduction to Molecular and Cell Biology - Photosynthesis
• BCcampus Open Publishing - Concepts of Biology – 1st Canadian Edition - Overview of Photosynthesis
• photosynthesis - Children's Encyclopedia (Ages 8-11)
• photosynthesis - Student Encyclopedia (Ages 11 and up)
• Table Of Contents

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

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

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

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

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

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

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

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

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

General characteristics

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

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

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

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

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

ENCYCLOPEDIC ENTRY

Photosynthesis.

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

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Learning materials, instructional links.

• Photosynthesis (Google doc)

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

The process

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

Chlorophyll

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

Light-dependent Reactions vs. Light-independent Reactions

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

C3 and C4 Photosynthesis

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

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Photosynthesis

Reviewed by: BD Editors

Photosynthesis Definition

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

Photosynthesis Equation

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

Stages of Photosynthesis

The light reactions.

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

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

The Calvin Cycle

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

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

Products of Photosynthesis

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

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

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Microbe Notes

Photosynthesis: Equation, Steps, Process, Diagram

Photosynthesis is defined as the process, utilized by green plants and photosynthetic bacteria, where electromagnetic radiation is converted into chemical energy and uses light energy to convert carbon dioxide and water into carbohydrates and oxygen.

• The carbohydrates formed from photosynthesis provide not only the necessary energy form the energy transfer within ecosystems, but also the carbon molecules to make a wide array of biomolecules.
• Photosynthesis is a light-driven oxidation-reduction reaction where the energy from the light is used to oxidize water, releasing oxygen gas and hydrogen ions, followed by the transfer of electrons to carbon dioxide, reducing it to organic molecules.
• Photosynthetic organisms are called autotrophs because they can synthesize chemical fuels such as glucose from carbon dioxide and water by utilizing sunlight as an energy source.
• Other organisms that obtain energy from other organisms also ultimately depend on autotrophs for energy.
• One of the essential requirements for photosynthesis is the green pigment ‘chlorophyll’ which is present in the chloroplasts of green plants and some bacteria.
• The pigment is essential for ‘capturing’ sunlight which then drives the overall process of photosynthesis.

Table of Contents

Interesting Science Videos

Photosynthesis equations/reactions/formula

• The process of photosynthesis differs in green plants and sulfur bacteria.
• In plants, water is utilized along with carbon dioxide to release glucose and oxygen molecules.
• In the case of sulfur bacteria, hydrogen sulfide is utilized along with carbon dioxide to release carbohydrates, sulfur, and water molecules.

Oxygenic Photosynthesis

The overall reaction of photosynthesis in plants is as follows:

Carbon dioxide + Water  + solar energy → Glucose + Oxygen

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

Carbon dioxide + Water  + solar energy → Glucose + Oxygen + Water

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

Anoxygenic Photosynthesis

The overall reaction of photosynthesis in sulfur bacteria is as follows:

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

Video Animation: Photosynthesis (Crash Course)

Photosynthetic pigments

• Photosynthetic pigments are the molecules involved in absorbing electromagnetic radiation, transferring the energy of the absorbed photons to the reaction center, resulting in photochemical reactions in the organisms capable of photosynthesis.
• The molecules of photosynthetic pigments are quite ubiquitous and are always composed of chlorophylls and carotenoids.
• In addition to chlorophyll, photosynthetic systems also contain another pigment, pheophytin (bacteriopheophytin in bacteria), which plays a crucial role in the transfer of electrons in photosynthetic systems.
• Moreover, other pigments can be found in particular photosynthetic systems, such as xanthophylls in plants.

Image Source: Simply Science .

Chlorophyll

• Chlorophyll is the pigment molecule, which is the principal photoreceptor in the chloroplasts of most green plants.
• Chlorophylls consist of a porphyrin ring, which is bounded to an ion Mg 2+ , attached to a phytol chain.
• Chlorophylls are very effective photoreceptors because they contain networks of alternating single and double bonds.
• In chlorophyll, the electrons are not localized to a particular atomic nucleus and consequently can more readily absorb light energy.
• In addition, chlorophylls also have solid absorption bands in the visible region of the spectrum.
• Chlorophylls are found either in the cytoplasmic membranes of photosynthetic bacteria, or thylakoid membranes inside plant chloroplasts.

Bacteriorhodopsin

• Bacteriorhodopsin is another class of photosynthetic pigment that exists only in halobacteria.
• It is composed of a protein attached to a retinal prosthetic group.
• This pigment is responsible for the absorption of light photons, leading to a conformational change in the protein, which results in the expulsion of the protons from the cell.

Phycobilins

• Cyanobacteria and red algae employ phycobilins such as phycoerythrobilin and phycocyanobilin as their light-harvesting pigments.
• These open-chain tetrapyrroles have the extended polyene system found in chlorophylls, but not their cyclic structure or central Mg 2+ .
• Phycobilins are covalently linked to specific binding proteins, forming phycobiliproteins, which associate in highly ordered complexes called phycobilisomes that constitute the primary light-harvesting structures in these microorganisms.

Carotenoids

• In addition to chlorophylls, thylakoid membranes contain secondary light-absorbing pigments, or accessory pigments, called carotenoids.
• Carotenoids may be yellow, red, or purple. The most important are β -carotene, which is a red-orange isoprenoid, and the yellow carotenoid lutein.
• The carotenoid pigments absorb light at wavelengths not absorbed by the chlorophylls and thus are supplementary light receptors.

Factors affecting photosynthesis

Blackman formulated the Law of limiting factors while studying the factors affecting the rate of photosynthesis. This Law states that the rate of a physiological process will be limited by the factor which is in the shortest supply. In the same way, the rate of photosynthesis is also affected by a number of factors, which are namely;

• As the intensity of light increases, the rate of light-dependent reactions of photosynthesis and in turn, the rate of photosynthesis increases.
• With increased light intensity, the number of photons falling on a leaf also increases. As a result, more chlorophyll molecules are ionized, and more ATPs and NADH are generated.
• After a point, however, the rate of photosynthesis remains constant as the light intensity increases. At this point, photosynthesis is limited by some other factors.
• Besides, the wavelength of light also affects the rate of photosynthesis.
• Different photosynthetic systems absorb light energy more effectively at different wavelengths.

Carbon dioxide

• An increase in the concentration of carbon dioxide increases the rate at which carbon is incorporated into carbohydrates in the light-independent reactions of photosynthesis.
• Thus, increasing the concentration of carbon dioxide in the atmosphere rapidly increases the rate of photosynthesis up to a point after which it is limited by some other factors.

Temperature

• The light-independent reactions of photosynthesis are affected by changes in temperature as they are catalyzed by enzymes, whereas the light-dependent reactions are not.
• The rate of the reactions increases as the enzymes reach their optimum temperature, after which the rate begins to decrease as the enzymes tend to denature.

Process/ Steps of Photosynthesis

The overall process of photosynthesis can be objectively divided into four steps/ process:

1. Absorption of light

• The first step in photosynthesis is the absorption of light by chlorophylls that are attached to the proteins in the thylakoids of chloroplasts.
• The light energy absorbed is then used to remove electrons from an electron donor like water, forming oxygen.
• The electrons are further transferred to a primary electron acceptor, quinine (Q) which is similar to CoQ in the electron transfer chain.

2. Electron Transfer

• The electrons are now further transferred from the primary electron acceptor through a chain of electron transfer molecules present in the thylakoid membrane to the final electron acceptor, which is usually NADP + .
• As the electrons are transferred through the membrane, protons are pumped out of the membrane, resulting in the proton gradient across the membrane.

3. Generation of ATP

• The movement of protons from the thylakoid lumen to the stroma through the F 0 F 1 complex results in the generation of ATP from ADP and Pi.
• This step is identical to the step of the generation of ATP in the electron transport chain .

4. Carbon Fixation

• The NADP and ATP generated in steps 2 and 3 provide energy, and the electrons drive the process of reducing carbon into six-carbon sugar molecules.
• The first three steps of photosynthesis are directly dependent on light energy and are thus, called light reactions, whereas the reactions in this step are independent of light and thus are termed dark reactions.

Types/ Stages/ Parts of photosynthesis

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

Photosynthesis is divided into two stages based on the utilization of light energy:

1. Light-dependent reactions

• The light-dependent reactions of photosynthesis only take place when the plants/ bacteria are illuminated.
• In the light-dependent reactions, chlorophyll and other pigments of photosynthetic cells absorb light energy and conserve it as ATP and NADPH while simultaneously, evolving O 2 gas.
• In the light-dependent reactions of photosynthesis, the chlorophyll absorbs high energy, short-wavelength light, which excites the electrons present inside the thylakoid membrane.
• The excitation of electrons now initiates the transformation of light energy into chemical energy.
• The light reactions take in two photosystems that are present in the thylakoid of chloroplasts.

Figure: Light-dependent reactions of photosynthesis in the thylakoid membrane of plant cells. Image Source: Wikipedia (Somepics) .

Photosystem II

• Photosystem II is a group of proteins and pigments that work together to absorb light energy and transfer electrons through a chain of molecules until it finally reaches an electron acceptor.
• Photosystem II has a pair of chlorophyll molecules, also known as P680 as the molecules best absorb light of the wavelength 680 nm.
• The P680 donates a pair of electrons after absorbing light energy, resulting in an oxidized form of P680.
• Finally, an enzyme catalyzes the splitting of a water molecule into two electrons, two hydrogen ion, and oxygen molecules.
• This pair of electrons then are transferred to P680, causing it to return to its initial stage.

Photosystem I

• Photosystem I is a similar complex like photosystem II except for that photosystem I have a pair of chlorophyll molecules known as P700 as they best absorb the wavelength of 700 nm.
• As photosystem I absorb light energy, it also becomes excited and transfers electrons.
• The now oxidized form of P700 then accepts an electron from photosystem II, restring back to its initial stage.
• The electrons from photosystem I are then passed in a series of redox reactions through the protein ferredoxin.
• The electrons finally reach NADP + , reducing them to NADPH.

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

Video Animation: The Light Reactions of Photosynthesis (Ricochet Science)

2. Light independent reactions (Calvin cycle)

Light independent reactions of photosynthesis are anabolic reactions that lead to the formation of a sex-carbon compound, glucose in plants. The reactions in this stage are also termed dark reactions as they are not directly dependent on the light energy but do require the products formed from the light reactions.

Figure: Overview of the Calvin cycle pathway. Image Source: Wikipedia (Mike Jones) .

This stage consists of 3 further steps that lead to carbon fixation/ assimilation.

Step 1: Fixation of CO 2 into 3-phosphoglycerate

• In this step, one CO 2 molecule is covalently attached to the five-carbon compound ribulose 1,5-biphosphate catalyzed by the enzyme ribulose 1,5-biphosphate carboxylase, also called rubisco.
• The attachment results in the formation of an unstable six-carbon compound that is then cleaved to form two molecules of 3-phosphoglycerate.

Step 2: Conversion of 3-phosphoglycerate to glyceraldehydes 3-phosphate

• The 3-phosphoglycerate formed in step 1 is converted to glyceraldehyde 3-phosphate by two separate reactions.
• At first, enzyme 3-phosphoglycerate kinase present in the stroma catalyzes the transfer of a phosphoryl group from ATP to 3-phosphoglycerate, yielding 1,3-bisphosphoglycerate.
• Next, NADPH donates electrons in a reaction catalyzed by the chloroplast-specific isozyme of glyceraldehyde 3-phosphate dehydrogenase, producing glyceraldehyde 3-phosphate and phosphate (Pi).
• Most of the glyceraldehyde 3-phosphate thus produced is used to regenerate ribulose 1,5-bisphosphate.
• The rest of the glyceraldehyde is either converted to starch in the chloroplast and stored for later use or is exported to the cytosol and converted to sucrose for transport to growing regions of the plant.

Step 3: Regeneration of ribulose 1,5-biphosphate from triose phosphates

• The three-carbon compounds formed in the previous steps are then converted into the five-carbon compound, ribulose 1,5-biphosphate through a series of transformations with intermediates of three-, four,-, five-, six-, and seven-carbon sugar.
• As the first molecules in the process, if regenerated, this stage of photosynthesis results in a cycle (Calvin cycle).

3 CO 2 + 9 ATP + 6 NADPH + 6 H +     →     glyceraldehyde-3-phosphate (G3P) + 9 ADP + 8 P i  + 6 NADP +  + 3 H 2 O

A G3P molecule contains three fixed carbon atoms, so it takes two G3Ps to build a six-carbon glucose molecule. It would take six turns of the cycle to produce one molecule of glucose.

Video Animation: The Calvin Cycle (Ricochet Science)

Products of Photosynthesis

The outcomes of light-dependent reactions of photosynthesis are:

The products of light-independent reactions (Calvin cycle) of photosynthesis are:

• glyceraldehyde-3-phosphate (G3P) / Glucose (carbohydrates)

The overall products of photosynthesis are:

• Glucose (carbohydrates)
• Sulfur (in photosynthetic sulfur bacteria)

Photosynthesis Examples

Photosynthesis in green plants or oxygenic bacteria.

• In plants and oxygenic bacteria like cyanobacteria, photosynthesis takes place in the presence of green pigment, chlorophyll.
• It takes place in the thylakoids of the chloroplasts, resulting in products like oxygen gas, glucose, and water molecules.
• Most of the glucose units in plants are linked to form starch or fructose or even sucrose.

Photosynthesis in sulfur bacteria

• In purple sulfur bacteria, photosynthesis takes place in the presence of hydrogen sulfur rather than water.
• Some of these bacteria like green sulfur bacteria have chlorophyll whereas other purple sulfur bacteria have carotenoids as photosynthetic pigments.
• The result of photosynthesis in these bacteria are carbohydrates (not necessarily glucose), sulfur gas, and water molecules.

Importance of photosynthesis

• Photosynthesis is the primary source of energy in autotrophs where they make their food by utilizing carbon dioxide, sunlight, and photosynthetic pigments.
• Photosynthesis is equally essential for heterotrophs, as they derive their energy from the autotrophs.
• Photosynthesis in plants is necessary to maintain the oxygen levels in the atmosphere.
• Besides, the products of photosynthesis contribute to the carbon cycle occurring in the oceans, land, plants, and animals.
• Similarly, it also helps maintain a symbiotic relationship between plants, animals, and humans.
• Sunlight or solar energy is the primary source of all other forms of energy on earth, which is utilized through the process of photosynthesis.

Artificial photosynthesis

Artificial photosynthesis is a chemical process that mimics the biological process of utilization of sunlight, water and carbon dioxide to produce oxygen and carbohydrates.

Image Source: Phys .

• In artificial photosynthesis, photocatalysts are utilized that are capable of replicating the oxidation-reduction reactions taking place during natural photosynthesis.
• The main function of artificial photosynthesis is to produce solar fuel from sunlight that can be stored and used under conditions, where sunlight is not available.
• As solar fuels are prepared, artificial photosynthesis can be used to produce just oxygen from water and sunlight, resulting in clean energy production.
• The most important part of artificial photosynthesis is the photocatalytic splitting of a water molecule, resulting in oxygen and large quantities of hydrogen gas.
• Further, light-driven carbon reduction can also be performed to replicate the process of natural carbon fixation, resulting in carbohydrates molecules.
• Thus, artificial photosynthesis has applications in the production of solar fuels, photoelectrochemistry, engineering of enzymes, and photoautotrophic microorganisms for the production of microbial biofuel and biohydrogen from sunlight.

Video Animation: Learning from leaves: Going green with artificial photosynthesis

Photosynthesis vs. Cellular respiration

Image Source: Khan Academy .

Video Animation: Photosynthesis vs. Cellular Respiration Comparison (BOGObiology)

FAQs (Revision Questions)

Where does photosynthesis occur? Photosynthesis occurs in the thylakoid membrane of the chloroplasts.

What are the products of photosynthesis? The products of photosynthesis are carbohydrates (glucose), oxygen, and water molecules.

What are the reactants of photosynthesis? The reactants of photosynthesis are carbon dioxide, water, photosynthetic pigments, and sunlight.

How are photosynthesis and cellular respiration related? Photosynthesis and cellular respiration are essentially the reverses of one another where photosynthesis is an anabolic process resulting in the formation of organic molecules. In contrast, cellular respiration is a catabolic process resulting in the breaking down of organic molecules to release energy.

• Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 17.2, Entry to the Citric Acid Cycle and Metabolism Through It Are Controlled.Available from: https://www.ncbi.nlm.nih.gov/books/NBK22347/
• Nelson DL and Cox MM. Lehninger Principles of Biochemistry. Fourth Edition.
• Montero F. (2011) Photosynthetic Pigments. In: Gargaud M. et al. (eds) Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg
• Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Section 16.3, Photosynthetic Stages and Light-Absorbing Pigments.Available from: https://www.ncbi.nlm.nih.gov/books/NBK21598/

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Anupama Sapkota

1 thought on “Photosynthesis: Equation, Steps, Process, Diagram”

How can we say that 6 calvin cycles are needed to produce 1 glucose molecule why not 2?

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BIOLOGY JUNCTION

Test And Quizzes for Biology, Pre-AP, Or AP Biology For Teachers And Students

Photosynthesis

I. Capturing the Energy of Life

• All organisms require energy
• Some organisms (autotrophs) obtain energy directly from the sun and store it in organic compounds (glucose) during a process called photosynthesis

6CO2 + 6H2O + energy –>  6O2 + C6H12O6

II. Energy for Life Processes

• Energy is the ability to do work
• Work for a cell includes growth & repair, active transport across cell membranes, reproduction, synthesis of cellular products, etc.
• Work is the ability to change or move matter against other forces (W = F x D)
• Autotrophs or producers convert sunlight, CO2, and H2O into glucose (their food)
• Plants, algae, and blue-green bacteria, some prokaryotes, are producers or autotrophs
• Only 10% of the Earth’s 40 million species are autotrophs
• Other autotrophs use inorganic compounds instead of sunlight to make food; process known as chemosynthesis
• Producers make food for themselves and heterotrophs or consumers that cannot make food for themselves
• Heterotrophs include animals, fungi, & some bacteria, & protists

III.        Biochemical Pathways

• Photosynthesis and cellular respiration are biochemical pathways
• Biochemical pathways are a series of reactions where the product of one reaction is the reactant of the next
• Only autotrophs are capable of photosynthesis
• Both autotrophs & heterotrophs perform cellular respiration to release energy to do work
• In photosynthesis, CO2(carbon dioxide) and H2O (water) are combined to form C6H12O6 (glucose) & O2 (oxygen) 6CO2 + 6H2O + energy –>  6O2 + C6H12O6
• In cellular respiration, O2 (oxygen) is used to burn C6H12O6 (glucose) & release CO2(carbon dioxide), H2O (water), and energy 
• Usable energy released in cellular respiration is called adenosine triphosphate or ATP

IV. Light Absorption in Chloroplasts

• Chloroplasts in plant & algal cells absorb light energy from the sun during the light dependent reactions
• Photosynthetic cells may have thousands of chloroplasts
• Chloroplasts are double membrane organelles with the an inner membrane folded into disc-shaped sacs called thylakoids
• Thylakoids, containing chlorophyll and other accessory pigments , are in stacks called granum (grana, plural)
• Grana are connected to each other & surrounded by a gel-like material called stroma
• Light-capturing pigments in the grana are organized into photosystems

 V. Pigments

• Light travels as waves & packets called photons
• Wavelength of light is the distance between 2 consecutive peaks or troughs

• Sunlight or white light is made of different wavelengths or colors carrying different amounts of energy
• A prism separates white light into 7 colors (red, orange, yellow, green, blue, indigo, & violet) ROY G. BIV
• These colors are called the visible spectrum

• When light strikes an object, it is absorbed, transmitted, or reflected
• When all colors are absorbed, the object appears black
• When all colors are reflected, the object appears white
• If only one color is reflected (green), the object appears that color (e.g. Chlorophyll)

• Thylakoids contain a variety of pigments ( green red, orange, yellow…)
• Chlorophyll  (C55H70MgN4O6 ) is the most common pigment in plants & algae
• Chlorophyll a & chlorophyll b are the 2 most common types of chlorophyll in autotrophs
• Chlorophyll absorbs only red, blue, & violet light
• Chlorophyll b absorbs colors or light energy NOT absorbed by chlorophyll a
• The light energy absorbed by chlorophyll b is transferred to chlorophyll a in the light reactions
• Carotenoids are accessory pigments in the thylakoids & include yellow, orange, & red

VII. Overview of Photosynthesis         6CO2 + 6H2O C6H12O6 + 6O2

• Photosynthesis is not a simple one step reaction but a biochemical pathway involving many steps
• This complex reaction can be broken down into  two reaction systems — light dependent & light independent or dark reactions
• Water is split, giving off oxygen.
• This system depends on sunlight for activation energy.
• Light is absorbed by chlorophyll a which “excites” the electrons in the chlorophyll molecule.
• Electrons are passed through a series of carriers and adenosine triphosphate or ATP (energy) is produced.
• Takes place in the thylakoids.
• Carbon dioxide is split, providing carbon to make sugars.
• The ultimate product is glucose.
• While this system depends on the products from the light reactions, it does not directly require light energy.
• Includes the Calvin Cycle.
• Takes place in the stroma.

VIII. Calvin Cycle

• Carbon atoms from CO2 are bonded or “fixed” into organic compounds during a process called carbon fixation
• The energy stored in ATP and NADPH during the Light Reactions is used in the Calvin cycle
• The Calvin cycle has 3 main steps occurring within the stroma of the Chloroplast

     STEP 1

• CO2 diffuses into the stroma from surrounding cytosol
• An enzyme combines a CO2 molecule with a five-carbon carbohydrate called RuBP
• The six-carbon molecule produced then splits immediately into a pair of three-carbon molecules known as PGA

      STEP 2

• Each PGA molecule receives a phosphate group from a molecule of ATP
• This compound then receives a proton from NADPH and releases a phosphate group producing PGAL
• These reactions produce ADP, NADP+, and phosphate which are used again in the Light Reactions.
• Most PGAL is converted back to RuBP to keep the Calvin cycle going
• Some PGAL leaves the Calvin Cycle and is used to make other organic compounds including amino acids, lipids, and carbohydrates
• PGAL serves as the starting material for the synthesis of glucose and fructose
• Glucose and fructose make the disaccharide sucrose , which travels in solution to other parts of the plant (e.g., fruit, roots)
• Glucose is also the monomer used in the synthesis of the polysaccharides starch and cellulose

• Each turn of the Calvin cycle fixes One CO2 molecule so it takes six turns to make one molecule of glucose

IX. Photosystems & Electron Transport Chain

• Only 1 in 250 chlorophyll molecules (chlorophyll a) actually converts light energy into usable energy
• These molecules are called reaction-center chlorophyll
• The other molecules (chlorophyll b, c, & d and carotenoids) absorb light energy and deliver it to the reaction-center molecule
• These chlorophyll molecules are known as antenna pigments
• A unit of several hundred antenna pigment molecules plus a reaction center is called a photosynthetic unit or photosystem
• There are 2 types of photosystems — Photosystem I & Photosystem II
• Light is absorbed by the antenna pigments of photosystems II and I
• The absorbed energy is transferred to the reaction center pigment, P680 in photosystem II, P700 in photosystem I
• P680 in Photosystem II loses an electron and becomes positively charged so it can now split water & release electrons  (2H2O   4H+   +   4e-   +  O2)
• Electrons from water are transferred to the cytochrome complex of Photosystem I
• These excited electrons activate P700 in photosystem I which helps reduce NADP+ to NADPH
• NADPH is used in the Calvin cycle
• Electrons from Photosystem II replace the electrons that leave chlorophyll molecules in Photosystem I

• Synthesis or making of ATP (energy)
• Depends on the concentration gradient of protons ( H+) across the thylakoid membrane
• Protons (H+) are produced from the splitting of water in Photosystem II
• Concentration of Protons is HIGHER in the thylakoid than in the stroma
• Enzyme, ATP synthetase in the thylakoid membrane, makes ATP by adding a phosphate group to ADP

XI. Alternate Pathways

• The Calvin cycle is the most common pathway used by autotrophs called C3 Plants
• Plants in hot, dry climates use alternate pathways to fix carbon & then transfer it to the Calvin cycle
• Stomata are small openings on the underside of leaves for gas exchange (O2 & CO2)
• Guard cells on each side of the stoma help open & close the stomata
• Plants also lose H2O through stoma so they are closed during the hottest part of the day

• C4 plants  fix CO2 into 4-Carbon Compounds during the hottest part of the day when  their stomata are partially closed
• C4 plants include corn, sugar cane and crabgrass
• CAM plants include cactus & pineapples
• CAM plants open their stomata at night and close during the day so CO2 is fixed at night
• During the day, the CO2 is released from these compounds and enters the Calvin Cycle

XII. Factors Determining the Rate of Photosynthesis

• Light intensity – As light intensity increases, the rate of photosynthesis initially increases and then levels off to a plateau
• Temperature – Only the dark, not the light reactions are temperature dependent because of the enzymes they use ( 25 oC to 37oC)
• Length of day
• Increasing the amount of carbon dioxide available improves the photosynthesis rate
• Level of air pollution

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

What is photosynthesis, 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.

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):

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:

Photosynthesis equations/reactions/formula

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​

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:

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.

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

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

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

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:

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:

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.

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.

Organelle for Photosynthesis

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:

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

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.

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.

3. Photophosphorylation:

Wavelengths of light involved and their absorption.

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:

Absorption spectrum and action spectrum

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

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:

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

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.

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

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.

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

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.

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.

Products of Photosynthesis

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

Process of Photosynthesis – Overview

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.

Photosynthesis examples

Importance of photosynthesis.

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?

Photosynthesis vs cellular respiration.

Evolution of Photosynthesis

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.

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.

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.

Quiz Practice

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

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

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

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

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

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

Where does photosynthesis take place?

What are the reactants of photosynthesis, 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?

Where does photosynthesis occur, what are the products of photosynthesis, 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-

What are the raw materials of photosynthesis, 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

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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?

How does photosynthesis start?

• Location of photosynthesis

Light-dependent reactions

• The Calvin cycle

Types of photosynthesis

Additional resources.

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

Types of photosynthetic processes

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

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

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

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

The Photosynthesis equation

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

The oxygenic photosynthesis equation is: 

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

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

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

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

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

How is carbon dioxide and oxygen exchanged?

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

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

How do plants absorb sunlight for photosynthesis?

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

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

Related: What if humans had photosynthetic skin?

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

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

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

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

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

Where in the plant does photosynthesis take place?

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

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

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

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

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

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

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

Light-independent reactions: The Calvin cycle

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

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

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

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

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

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

C3 photosynthesis

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

C4 photosynthesis

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

CAM photosynthesis

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

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

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

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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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Photosynthesis ( CIE IGCSE Biology )

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Biology Lead

Photosynthesis

• Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water
• At the same time oxygen is made and released as a waste product
• The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun
• So photosynthesis can be defined as t he process by which plants manufacture carbohydrates from raw materials using energy from light
• It can be summed up in the following equation:

If asked for the raw materials required for photosynthesis, the answer is carbon dioxide and water.

Although required for the reaction to take place, light energy is not a substance and therefore cannot be a raw material.

Photosynthesis Word Equation

Photosynthesis word equation

How plants get the materials they need

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NEET Biology Photosynthesis in Higher Plants Class 11 Notes

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• Photosynthesis In Higher Plants

Photosynthesis in Higher Plants Notes PDF for High Scores in NEET Biology

Class 11 Photosynthesis in Higher Plants is a fundamental chapter that elaborates on how a plant conducts the process of photosynthesis in its cell organelles. It explains the biochemical process of synthesising food by trapping solar energy using pigments and converting simpler molecules to complex ones. The outcome of photosynthesis forms the main source of food for almost all ecosystems. To understand the concepts of this chapter easily, refer to the Photosynthesis in Higher Plants Class 11 notes prepared by the subject matter experts of Vedantu.

Note: 👉 Get a Head Start on Your Medical Career with the NEET Rank and College Predictor 2024 .

These notes have been designed to offer a concise format of the entire chapter. The fundamental principles and every crucial concept are explained and described using simpler scientific language for NEET aspirants. Using these notes will enable students to complete revising this chapter faster without compromising on preparation quality.

Access NEET Revision Notes Biology Photosynthesis in Higher Plants

Introduction:.

Plants are the primary source of food for all animals on Earth, including humans. 

Green plants synthesise the food they require, and all other organisms rely on them to meet their energy requirements. They produce the food through photosynthesis and are thus classified as autotrophs because they prepare their own food. 

Heterotrophs, which include humans, are species that depend on green plants for nutrition. 

All living things on Earth rely on sunlight for energy. 

Photosynthesis is a biological process in which plants use light energy from the sun to fuel the formation of organic molecules like glucose. 

Photosynthesis is vital for two reasons: 

It is the prime source of all food on the planet.

Oxygen is emitted into the atmosphere (which is required for aerobic life to exist on this planet).

Photosynthesis requires three components: 

Chlorophyll, which is the green pigment found in leaves

Carbon dioxide.

Early Experiments:

Early Experiment of Photosynthesis Done by Joseph Priestly

Joseph Priestly, in 1774,  discovered that plants replenish oxygen in the air which respiratory animals and burning candles eliminate.

Julius von Sachs discovered in 1854 that the green parts of plants are where glucose is produced which is usually saved as starch.

T.W Engelmann (1843-1909) carried out a fantastic experiment. He used a prism to separate light into its spectrum components before lighting a green alga named Cladophora that was dissolved in an anaerobic bacteria solution. The microorganisms were used to discover where O 2 originated. He found that germs gathered primarily in the split spectrum's blue and red light areas. So, the first photosynthesis action spectrum was thus defined, resembling the absorption spectra pigments of chlorophyll a and b. 

The empirical equation then depicted the entire process of photosynthesis for oxygen-evolving organisms:$\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow\left[\mathrm{CH}_{2} \mathrm{O}\right]+\mathrm{O}_{2}$

where CH 2 O is a carbohydrate like glucose (6 carbon sugar).

Cornelius van Neill, a microbiologist, made notable participation in the understanding of photosynthesis by demonstrating that photosynthesis is a light-dependent reaction in which H 2 from an appropriate hydrogen compound, i.e. H 2 O, reduces carbon dioxide to carbohydrates.

The equation can be expressed as,

$2 \mathrm{H}_{2} \mathrm{~A}+\mathrm{CO}_{2} \xrightarrow{Light}  \mathrm{~A}+\mathrm{CH}_{2} \mathrm{O}+\mathrm{H}_{2} \mathrm{O}$

H 2 O is the H 2 donor in green plants and is oxidized to O 2 . Some life forms do not produce O 2 during photosynthesis.  As a result, it is deduced that O 2 created by plants (green) comes from H 2 O rather than CO 2 .

As a result, the photosynthesis equation is as follows:

$6\mathrm{CO}_{2}+12 \mathrm{H}_{2} \mathrm{O}\xrightarrow{Light} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+6 \mathrm{H}_{2} \mathrm{O}+6 \mathrm{O}_{2}$

Photosynthesis occurs in the chloroplasts of mesophyll cells of the green leaves, specifically in the green leaves of plants.

Chloroplast

The membrane system is responsible for capturing solar energy and producing ATP and NADPH; the reactions or set of reactions participating are light-driven and thus referred to as Light reactions .

Enzymes in the stroma are capable of taking CO 2 and converting it into sugar, which then forms starch; the reactions are not instantly light-driven but are reliant on the components of light reactions, namely ATP and NADPH, and are referred to as Dark reactions .

How Many Different Kinds of Pigments are Required in Photosynthesis?

In leaves, there are four pigments: chlorophyll-a (bluish-green), chlorophyll-b (yellowish-green), Xanthophylls (yellow), and carotenoids (yellow to yellow-orange).

Absorption spectrum of Chlorophyll-a, b, and Carotenoids

We can reach the conclusion that chlorophyll is the most important pigment involved in photosynthesis.

Light Reaction:

Light-harvesting Complexes

Absorption of light, splitting of water, releasing oxygen, and creating high-energy chemicals such as ATP and NADPH are all part of the process.

Several complexes, namely Light-harvesting complexes (LHC) with pigments in Photosystem-1 (PSI) and Photosystem-2 (PSII), are named in the order of their discovery.

Each photosystem, with the exception of chlorophyll a, contains all of the pigments and constitutes an LHS known as antennae.

The reaction centre is formed by a single molecule of chlorophyll-a.

PSI has a maximum absorption at 700 nm, thus is also known as P700 whereas PSII has a maximum absorption at 680 nm, which is known as P680.

Electron Transport System:

LHC of PSII receives light at 680 nanometers, which excites electrons, causing them to jump out of their orbit and be received by an electron acceptor, which then moves them to the electron transport system. 

Electrons are not used up and are transferred to PSI pigments. Because of the absorption of light at 700 nanometers, these electrons pass to an energy molecule NADP + , leading to the formation of NADPH and H + .

The Z scheme is the name given to this electron transport system.

The Z-scheme of Electron Transport System

Splitting of a Water Molecule:

The splitting of H 2 O replaces the electrons which were transferred from Photosystem-2. This produces oxygen, a byproduct of photosynthesis.

2 H 2 O ⟶ 4 H + + O 2 + 4 e -

PSII is associated with this splitting of H 2 O. It provides the electrons required to replace those eliminated from PSI.

Cyclic and Non-cyclic Photophosphorylation:

Cyclic Phosphorylation

Photophosphorylation is the process by which ATP is synthesised from ADP and Pi in the existence of light. 

Non-cyclic photophosphorylation occurs when PSII and then PSI act in series, resulting in the synthesis of both ATP and NADPH.

Cyclic photophosphorylation occurs when only PSI is active, the electron is distributed within PSI  and phosphorylation occurs as a result of the cyclic flow of electrons. It occurs in the stroma lamellae. It lacks the NADP reductase enzyme, so ATP is synthesised but not NADPH and H + .

It also takes place when only light with a wavelength greater than 680 nanometers is available.

Chemiosmosis Hypothesis:

Chemiosmosis Hypothesis

The ATP synthase enzyme is composed of two parts: F 0 and F 1 .

F 0 , which is presented into the thylakoid layer and creates a transmembrane channel that enables protons to easily diffuse across the layer. 

F 1 is the other half, which is situated on the stroma-facing side of the thylakoid external surface of the membrane. 

The gradient's breakdown offers enough energy to cause a conformational shift in the F 1 moiety of the ATP synthase, allowing the enzyme to synthesise multiple molecules of ATP. 

Chemiosmosis requires a membrane, a proton pump, a proton angle, and ATP synthase.

To create a gradient or a larger proportion of protons inside the thylakoid lumen, energy is used to pump protons across a membrane. 

ATP synthase contains a channel that allows protons to be released back across the membrane, releasing enough energy to activate the ATP synthase chemical, which catalyses the formation of ATP. 

Along with the NADPH produced by electron development.

Where Do ATP and NADPH Play a Role in Photosynthesis?

These are used in a dark reaction known as the biosynthetic phase of photosynthesis, where food is synthesised.

There are two pathways for the Dark reaction:

C 3 pathway or Calvin cycle

C 4 pathway or Hatch-Slack pathway

In the C 3 pathway, the first stable product of the carbon fixation is a three-carbon molecule like PGA (Phosphoglyceric acid) whereas, in the C 4 pathway, it is a four-carbon molecule like OAA (Oxaloacetate).

C 3 Pathway or Calvin Cycle:

Calvin Cycle

Melvin Calvin found that the first molecule of carbon dioxide fixation was a three-carbon organic acid named 3-phosphoglyceric acid or PGA, hence the Calvin cycle .

The primary CO 2 acceptor in this pathway or C 3 plants is a 5-C-containing RuBP (ribulose bisphosphate) molecule that integrates with CO 2 to generate sucrose.

Steps included in the Calvin Cycle 

Carboxylation:  In the availability of an enzyme known as RuBP carboxylase-oxygenase (RuBisCO), carbon dioxide is used for decarboxylation of RuBP, resulting in two molecules of 3-PGA. RuBisCO enzyme has an affinity for both carbon dioxide and oxygen.

Reduction: Carbon dioxide reduction requires two molecules of ATP for phosphorylation as well as two molecules of NADPH for reduction. Six carbon dioxide molecules must be fixed, as the cycle repeats six times.

Regeneration: To regenerate the carbon dioxide acceptor molecule RuBP, one ATP must be phosphorylated.

C 4 or Hatch-Slack Pathway:

Hatch-Slack Pathway

The mesophyll cells and vascular bundles are the two types of cells found in the C 4 plants. 

Bundle sheath cells are large cells that surround vascular bundles, and the leaves of these plants have kranz anatomy. 

Bundle sheath cells can have multiple layers of chloroplasts and are resistant to gaseous exchange. 

The mesophyll cells contain the three-carbon molecule called phosphoenolpyruvate (PEP), which serves as the primary carbon dioxide acceptor. 

The enzyme in charge is PEP carboxylase or PEP case, where the RuBisCO enzyme is missing.

C 4 acid OAA is formed here, which is then transferred to bundle sheath cells where C 4 acids are split to release carbon dioxide and a three-carbon molecule. 

It is then shipped to mesophyll, where it constructs PEP once more, completing the cycle.

The carbon dioxide produced in the bundle sheath cells reaches the C 3 / Calvin pathway, which is shared by all plants, C 3 or C 4 . 

The enzyme RuBisCO is abundant in the bundle sheath cells, but PEPcase is lacking. Carbon dioxide gas concentration rises as bundle sheath cells become impermeable to it.

Photorespiration:

RuBisCO, the most abundant enzyme on the planet, is distinguished by its ability to bind both O 2 and CO 2 .

Some O 2 binds with RuBisCO in C 3 plants, leading to the formation of phosphoglycerate and phosphoglycolate via a pathway known as photorespiration. 

Because there is no production of sugar or ATP/NADPH in this pathway, it is referred to as a wasteful process.

Photorespiration does not occur in C 4 plants, so they are more productive.

Factors Influencing Photosynthesis: 

The photosynthesis rate is affected by both internal and external factors.

Internal factors such as the number, size, age, alignment of leaves, chloroplasts, and so on, as well as external factors such as CO 2 concentration, temperature, water, and so on.

When many factors affect any biological process, Blackman's (1905) Law of Limiting Factors comes into play, which states that if a chemical process is affected by more than one factor, the rate will be determined by the factor that is nearest to its minimal value, which is known as the Limiting factor. 

If the amount is changed, the figure identifies the exact method.

Light is being used as 10% of the incident sunlight.

It is directly proportional to CO 2 fixation at low intensities. Other factors become confining as the intensity increases.

Excessive light causes the breakdown of chlorophyll, resulting in a decrease in photosynthesis.

Concentration of Carbon Dioxide

As carbon dioxide concentrations in the atmosphere are very low, ranging from 0.03 to 0.04 percent, an increase in concentration of up to 0.05 percent can cause an increase in photosynthesis rate.

Temperature

Because the dark reactions are enzymatic, they are temperature controlled. C 4 plants react to higher temperatures and have higher photosynthesis rates, whereas C 3 plants have a lower temperature optimum.

Water stress leads to closing of stomata, reducing carbon dioxide accessibility, and causes leaves to wilt, thus reducing the surface area.

Key Points to Remember:

Photosynthesis is the process by which green plants produce their own food.

Carbon dioxide from the environment is obtained by leaves via stomata and used to make carbohydrates, primarily glucose and starch, during this process.

Photosynthesis occurs only in the green parts of plants, primarily the leaves. 

The mesophyll cells in the leaves contain a large number of chloroplasts, which are capable of CO 2 fixation. 

The light reaction happens within the chloroplasts, while the chemosynthetic process occurs in the stroma. 

The light reaction and the reactions of carbon fixing are the two stages of photosynthesis. 

Light energy is absorbed by the pigments in the antenna and channelled to special chlorophyll molecules known as reaction centre chlorophylls during the light reaction.

PSI and PSII are the two photosystems. PSI's reaction centre is a 700 nm trapping chlorophyll, a P700 molecule, whereas PSII reaction centre is a P680 that consumes red light at 680 nm. 

After absorbing energy, electrons are emitted and relocated through PSII and PSI to NAD, where they combine to form NADH. 

During this process, a proton gradient is formed across the thylakoid membrane.

The loss of the protons gradient caused by movement through the   portion of the ATPase enzyme emits sufficient energy for ATP synthesis. 

PSII is correlated with water molecule splitting, which leads to the release of O 2 , protons, and electron transfer to PSII.

CO 2 is introduced by the enzyme RuBisCO to a 5-carbon compound RuBP, which is then converted into two molecules of 3-carbon PGA. 

The Calvin cycle then converts this to sugar, and the RuBP is recharged. 

ATP and NADPH produced during the light reaction are used in this process. RuBisCO also catalyses photorespiration, an inefficient oxygenation reaction in C 3 plants.

Some tropical plants exhibit a type of photosynthesis known as the C 4 pathway.

The first stable product of $C{O_2}$ fixation in the mesophyll in these plants is a 4-carbon compound. 

The Calvin pathway is used in bundle sheath cells to synthesise carbohydrates.

NEET Biology Photosynthesis in Higher Plants Flashcards 

Importance of NEET Class 11 Photosynthesis in Higher Plants

Photosynthesis can be coined as the most important biochemical reaction occurring in the leaves of plants that provide the prime source of energy to different ecosystems. It ensures the survival of a food chain. Plants are the producers of food and the consumers depend on them.

In this chapter, the biochemical process of photosynthesis taking place in different steps will be explained. All the steps have been explained with proper chemical equations. The scientific derivation of all these steps will guide students to understand the mechanism of the entire process in detail.

This chapter will also explain the background of discovering the mechanism of this reaction. The pictorial representation of this process will explain how and where such chemical reactions take place in the leaves. The Photosynthesis in Higher Plants notes for NEET will help you understand the scientific principles of this botanical biochemical reaction perfectly.

This chapter holds immense importance in the NEET Biology syllabus as it explains one of the most important life reactions occurring in nature. It explains how majestically a plant can trap solar energy and convert simple molecules like carbon dioxide and water into glucose, the main respiratory substrate used by animals to survive.

Benefits of Photosynthesis in Higher Plants Notes for NEET

These revision notes will offer the easiest explanation of this complex biochemical reaction occurring in the leaves of plants. Every step will be explained using a proper and concise explanation. The reactions will also have definite equations so that you can understand the reactants, products, and catalysts/enzymes used in every step.

The concise format of the notes will also enable you to focus on the fundamental principles and concepts related to this reaction. Rest assured that referring to these notes before an exam will reduce your preparation time considerably. After you have completed studying this chapter, Photosynthesis in Higher Plants notes will be the ideal study material to revise.

The easier format will also enable you to recall the concepts faster and accurately. It means you will not have to waste time in remembering the concepts while answering fundamental questions asked in NEET. You will be able to score better in this competitive exam.

Download Free Photosynthesis in Higher Plants Notes PDF

It is now easy to get the free version of these notes in PDF format. Download the notes today and refer to them at your convenience. You will now be able to resolve your queries without any hassle using Photosynthesis in Higher Plants Class 11 notes NEET at home. Clarify your doubts and understand all the concepts related to photosynthesis, pigments, reactions, etc. better.

NEET Biology Revision Notes - Chapter Pages

Other Important Links for NEET Biology Notes

Understanding photosynthesis in higher plants is crucial for NEET Biology. Focus on grasping the process of converting light energy into chemical energy, primarily occurring in chloroplasts. Key components include the light-dependent and light-independent reactions, where water and carbon dioxide are converted into oxygen and glucose. Pay close attention to factors affecting photosynthesis like light intensity, temperature, and carbon dioxide concentration. Memorize key molecules involved such as chlorophyll, ATP, and NADPH. Additionally, understand the significance of photosynthesis in sustaining life on Earth and its interconnectedness with other biological processes. Regular revision and practice questions will solidify comprehension.

FAQs on NEET Biology Photosynthesis in Higher Plants Class 11 Notes

1. Which pigment traps solar energy in plants?

Chlorophyll A, B, C, and D are the green pigments that trap the solar energy in the sunrays.

2. Which gas is required for photosynthesis to synthesise glucose?

Plants need carbon dioxide to synthesise glucose in their leaves.

3. Which gas is the by-product of photosynthesis?

Oxygen is the by-product of photosynthesis. It is produced due to the breakdown of water molecules during the chemical reactions of photosynthesis.

4. What are photosynthetic pigments?

The biochemical substances that can trap solar energy emitting from the sun and convert it into energy to use for promoting various biochemical reactions are called photosynthetic pigments.

5. What is the important note of photosynthesis in higher plants?

Higher plants perform photosynthesis in specialized organelles called chloroplasts. These chloroplasts contain chlorophyll pigments that trap sunlight to fuel the process.  This light-driven conversion of carbon dioxide and water into organic molecules (primarily glucose) is the foundation of most life on Earth, as plants provide the base of the food chain for most ecosystems.

6. What are the important points of photosynthesis in plants?

Light Dependent Reactions (Light Phase): Capture light energy and convert it into ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate).

Light Independent Reactions (Calvin Cycle): Use the energy from ATP and NADPH to fix carbon dioxide into organic molecules (sugars).

Location: Occurs primarily in the mesophyll cells of leaves.

Gas Exchange: Takes in carbon dioxide (CO2) and releases oxygen (O2).

7. Which plant has a high rate of photosynthesis?

Plants with C4 photosynthetic pathways, like corn and sugarcane, generally have higher rates of photosynthesis compared to plants with C3 pathways like most trees. C4 plants have a more efficient way to capture CO2, which can be limiting in hot and dry environments.

8. Where are ATP and NADPH used?

ATP: Provides energy for the Calvin Cycle to fix carbon dioxide into organic molecules.

NADPH: Supplies electrons and hydrogen ions for the Calvin Cycle to convert CO2 into sugars.

9. Can photosynthesis occur without sunlight?

No, sunlight is essential for photosynthesis. Light energy provides the power to drive the light-dependent reactions that generate ATP and NADPH, which are necessary for the Calvin Cycle to fix carbon dioxide.

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Photosynthesis in Higher Plants Class 11 Notes PDF (Handwritten & Short Notes)

The Photosynthesis in Higher Plants Class 11 notes is one of the important study tools while preparing for Class 11 Biology board exam and NEET exam. It is considered to be an important study tool as it explains all the topics and concepts in a broad way. Through this explanation, students can easily build a strong foundation for the chapter Photosynthesis in Higher Plants. Strong foundation can also be helpful in understanding further chapters in Class 11 Biology. 

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CBSE Biology Chapter 13 Photosynthesis in higher plants class 11 Notes Biology in PDF are available for free download in myCBSEguide mobile app. The best app for CBSE students now provides Photosynthesis in higher plants class 11 Notes Biology latest chapter wise notes for quick preparation of CBSE exams and school based annual examinations. Class 11 Biology notes on Chapter 13 Photosynthesis in higher plants class 11 Notes Biology are also available for download in CBSE Guide website.

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CBSE Quick Revision Notes CBSE Class-11 Biology CHAPTER-13 Photosynthesis in higher plants class 11 Notes Biology

Photosynthesis is a physico-chemical process by which green plants use light energy to drive the synthesis of organic compounds. It is an enzyme regulated anabolic process.

Early Experiments

• Joseph Priestley in 1770, on the basis of his experiments showed the essential role of air in growth of green plants. A mouse kept in closed space could get suffocated and die but if a mint plant is kept in bell jar neither candle will extinguish nor will the mouse die. He concluded that foul air produced by animal is converted into pure air by plants. Priestley discovered Oxygen gas in 1774.
• Julius Von Sachs in 1854 shows that green part in plants produces glucose which is stored as starch. Starch is the first visible product of photosynthesis.
• T.W.Engelmann (1843-1909) used prism to split light into its components and then illuminated Cladophora (an algae) placed in a suspension of aerobic bacteria. He found that bacteria accumulated in blue and red light of the split spectrum. He thus discovered the effect of different wavelength of light on photosynthesis (action spectrum).

Where Does Photosynthesis Takes Place?

• Chloroplasts are green plastids which function as the site of photosynthesis in eukaryotic photoautotrophs. Inside the leaves, chloroplast is generally present in mesophyll cells along their walls.
• Within the chloroplast there is a membranous system consisting of grana, the stroma lamellae and the fluid stroma.

Pigments involved in Photosynthesis – Chromatographic separation of leaf pigments are as follows-

Maximum absorption by chlorophyll a occurs in blue and red regions having higher rate of photosynthesis. So, chlorophyll a is the chief pigment.

• Other thylakoid pigments like chlorophyll b, xanthophyll and carotenoids are called accessary pigments that absorb light and transfer energy to chlorophyll a and protect them from photo-oxidation.

Light reaction

• Light reaction(photochemical phase) includes:
• Light absorption
• Water splitting
• Oxygen release
• Formation of high energy chemical intermediates (ATP and NADPH).
• The pigments are organized into two discrete LHC( light harvesting complex) within photosystem I and photosystem II.
• LHC are made up of hundreds of pigments molecules containing all pigments except single chlorophyll a molecules in each PS.
• The pigments in photosystem I and photosystem II absorbs the lights of different wavelength. Single chlorophyll a molecule makes the reaction centre . In PS I reaction centre has highest peak at 700nm, hence called P700. And PS II reaction centre has highest peak at 680 nm, so called P680.

The Electron Transport System

• Reaction centre of photosystem II absorbs light of 680 nm in red region and causing electron to become excited. These electrons are picked by an electron acceptor which passes to electron transport system consisting of cytochromes.
• Electrons are passed down the electron transport chain and then to the pigment of PS I.
• Electron in the PSI also get excited due to light of wavelength 700nm and are transferred to another accepter molecule having a greater redox potential.
• When electron passes in downhill direction, energy is released. This is used to reduce the ADP to ATP and NADP+ to NADPH. The whole scheme of transfer of electron is called Z-scheme due to its shape.
• Photolysis of water release electrons that provide electron to PS II. Oxygen is also released during this process.

• Difference between cyclic and non-cyclic photophosphorylation

Chemiosmotic Hypothesis of ATP FORMATION

This hypothesis was proposed by Mitchell in 1961. ATP synthesis is linked to development of proton gradient across the membrane of thylakoid and mitochondria.

The process that causes development of proton gradient across the membrane is-

• Splitting of water molecules occurs inside the thylakoid to produce hydrogen ion or proton.
• As electron passes through the photosystems, protons are transported across the membrane because primary acceptor of electron is located towards the outer side the membrane.
• The NADP reductase enzyme is located in the stroma side of membrane. Electrons come out from the acceptor of electron of PSI, protons are necessary for reduction of NADP+ to NADP + H+. These protons are also removed from the stroma. This creates proton gradient across the thylakoids membrane along with pH in the lumen.
• Gradient is broken down due to movement of proton across the membrane to the stroma through trans-membrane channel of F0 of ATPase. One part of this enzyme is embedded in membrane to form trans-membrane channel. The other portion is called F1that protrudes on the outer surface of thylakoid membrane which makes the energy packed ATP.
• ATP and NADPH produced due to movement of electron is used immediately to fix CO2 to form sugar.
• The product of light reaction used to drive the process leading to synthesis of sugar are called biosynthetic phase of photosynthesis.

Calvin Cycle/C3 cycle/Reductive Pentose Sugar Phosphate Pathway

Calvin cycle can be described under three stages: carboxylation, reduction and regeneration.

• Regeneration is the generation of RuBP molecules for the continuation of cycle. This process require one molecules of ATP.

Fig-Calvin Cycle/ C3 Cycle

C4 pathway/Hatch Slack Pathway

• This pathway was worked out by Hatch and Slack (1965, 1967), mainly operational in plants growing in dry tropical region like Maize, Sugarcane, Sorghum etc.
• OAA formed in mesophyll cell forms 4-carbon compound like malic acid or aspartic acid which is transported to bundle sheath cells.

Photorespiration

• It is a the light dependent process of oxygenation of RuBP and release of carbon dioxide by photosynthetic organs of plants.
• Photorespiration decreases the rate of photosynthesis when oxygen concentration is increased from 2-3% to 21%.
• Presence of light and higher concentration of Oxygen results in the binding of RuBisCO enzyme with O2 to form.

Factors affecting photosynthesis

• Light- as light intensity increases, the rate of photosynthesis also increases until light saturation point.
• Temperature- it does not influence the rate of photosynthesis directly but at higher temperature enzyme activity is inhibited due to denaturation of enzymes which affect the dark reaction.
• Water – due to increase in amount of water, rate of photosynthesis does not increase proportionally as after saturation no more water is required during photosynthesis.

Blackman’s Law of Limiting Factors states: If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: it is the factor which directly affects the process if its quantity is changed.

Photosynthesis in higher plants class 11 Notes

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Photosynthesis in higher plants class 11 Notes Biology. CBSE quick revision note for class-11 Mathematics, Physics, Chemistry, Biology and other subject are very helpful to revise the whole syllabus during exam days. The revision notes covers all important formulas and concepts given in the chapter. Even if you wish to have an overview of a chapter, quick revision notes are here to do if for you. These notes will certainly save your time during stressful exam days.

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Photosynthetic Pigments

Pigments are compounds that give colour to materials around us. The substances that give this colour are also termed as biochromes or biological pigments. They are usually insoluble in water and are of two types – organic (natural) and inorganic (synthetic). Photosynthetic pigments are a type of natural pigment that helps in the process of photosynthesis. Here, let’s discuss more about the different types of photosynthetic pigments.

Table of Contents

Groups of pigments, functions of photosynthetic pigments, frequently asked questions.

Photosynthetic pigments are the most important coloured components of the chloroplast lamellae. These pigments are molecules that strongly absorb visible light. They interact with sunlight to alter the wavelengths that are either reflected or transmitted by the plant tissue. These pigments are also found in cyanobacteria and algae.

The major groups of photosynthetic pigments are:

Chlorophyll

Carotenoids, phycobilins.

The most widespread pigment in photosynthetic plants is chlorophyll. They are cyclic tetrapyrrole pigments chelated with magnesium. They share structural features with the haem and bile pigments of animals. These chlorophyll pigments can be found in fruits, flowers as well as leaves.

Chlorophyll a and chlorophyll b are the major types of chlorophylls found in plants. The former is a blue-green pigment and the latter is a yellow-green pigment. They give their characteristic green colour due to the strong absorbance of red and blue light. The other types of chlorophyll include chlorophyll c 1 , c 2 , c 3 , d, e and chlorophyll f.

Achlorophyllous – Achlorophyllous is a term used to describe an organism without chlorophyll and thus not able to take part in photosynthesis.

Carotenoids are also associated with the process of photosynthesis. Additionally, they give a bright colour to the fruits and flowers. They are terpenoid pigments present in all photosynthetic plants and they also occur in photosynthetic bacteria such as Rhodobacter and Erwinia . Carotenoids are orange, red and yellow pigments that usually occur in the roots, tubers, leaves, fruits, seeds and flowers.

This group includes the xanthophylls (yellow pigments) and carotenes (orange pigments).

• Zeaxanthin (xanthophyll) – yellow of corn seeds
• β carotene – orange peel

It is a light-capturing bile pigment found in the chloroplast of red algae and cyanobacteria. They have chromatophores that are primarily responsible for their colour. These are unique pigments as they are bonded to water-soluble phycobiliproteins which pass sunlight to chlorophyll and thus help in the process of photosynthesis.

Flavonoids are another type of commonly-found pigment, which are phenylpropanoid compounds. There are several classes of flavonoids out of which only a few provide pigments to plants like the proanthocyanidins (condensed tannins) and anthocyanins. Flavonoids occur in almost all tissues. Apart from providing floral pigmentation, they are also involved in nitrogen fixation, physiological regulation, UV filtration, etc.

Chlorophylls and carotenoids are required for photosynthesis. Chlorophylls are essential for the capture of light energy and are the primary electron donors. Carotenoids are essential structural components of the photosynthetic apparatus, where they protect against photo-oxidation. Plant pigments are also involved in other interactions of plants with light, in particular, the response to UV radiation.

With the exception of chlorophyll, the most obvious function of plant pigments is to provide colour to fruits and flowers and aid in pollination. Anthocyanins often occur in vegetative tissues. They contribute to the autumn colour in leaves of many deciduous species, which they generate in combination with the retention of carotenoids and loss of chlorophyll. In some cases, anthocyanin production is induced in response to stress like pests, pathogens, cold, nutrient deficiency, etc.

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