early experiments of photosynthesis

• Biology Article
• Photosynthesis Early Experiments

Early Experiments on Photosynthesis

Table of contents, introduction, photosynthesis discovery – early experiments, experiment to prove carbon dioxide is essential for photosynthesis, other experiments.

Photosynthesis is a light-dependant process that plants use to produce their own food. It is the process by which plants convert light energy into chemical energy, which can be used later for plants’ own processes. During this process, oxygen is produced as a byproduct. Photosynthesis was discovered only in 1800. To prove the existence of photosynthesis in plants, many scientists performed numerous experiments.

Let us have a detailed look at the early experiments on photosynthesis.

Also Read:  What is Photosynthesis

Since photosynthesis is a light-dependant process, it only takes place in the presence of sunlight. But along with sunlight, the plant also requires water and carbon dioxide as raw materials for this process to synthesise carbohydrates. Green plants also possess a green pigment known as chlorophyll which helps in capturing light energy. All these key features of photosynthesis were revealed later during the mid-nineteenth century when numerous scientific studies were conducted on photosynthesis.

Below mentioned are the experiments that were conducted by the early scientists in support of photosynthesis.

Materials required: A healthy potted plant, a wide-mouthed glass bottle with a split cork, potassium hydroxide solution (KOH), and starch solution.

Experiment:

• Select a healthy potted plant and place it in the darkroom for two to three days to ensure the leaves are free from starch.
• In a wide-mouthed glass bottle, add 10-15 ml of potassium hydroxide solution and split the cork vertically.
• Now carefully insert half part of a leaf into a glass bottle through the split cork and the other half exposed to air.
• Place the complete unit undisturbed in sunlight for about 3 – 4 hours.
• After 4 hours, detach the leaf from the plant and slowly remove it from the bottle and test it with the starch solution.
• We can observe that the half part leaf which was inside the glass bottle (KOH solution) did not show any colour change, but the other half part exposed to the surroundings turned its colour to dark brown, indicating the presence of starch in it.

Conclusion: In this experiment, we can conclude that carbon dioxide is essential for photosynthesis. Both the portion of the leaf received the same amount of water, chloroplasts , and sunlight but the half part which was inside the glass bottle did not receive carbon dioxide.

After discovering the importance of carbon dioxide in photosynthesis, many experiments were conducted to understand other essential factors for this process. Joseph Priestly was one of the first scientists to perform these experiments.

Experiment by Joseph Priestley

In 1770, after a series of experiments, Joseph Priestley came to a conclusion regarding the essentiality of air for photosynthesis and also for the growth of plants.

Materials required: A bell jar, candle, rat, and a plant.

• Priestley kept a burning candle and a rat together in the single bell jar.
• After some time, the candle was extinguished, and the rat died.
• For the second time, he kept a burning candle, a rat, and a green plant together in the bell jar.
• He observed that neither the candle got extinguished nor did the rat die.

Conclusion: Based on his observations, Priestley concluded that in the first case, the air in the bell jar got polluted by the candle and rat. However, in the second case, the plant reinstated the air that was spoiled by the candle and the rat.

But it took another few years to reveal what was exactly released by the plant to keep the rat alive and the candle burning.

Jan Ingenhousz: He proved that sunlight is essential for the photosynthesis process during which carbon dioxide is used and oxygen is produced.

Jean Senebier: He demonstrated that during photosynthesis, carbon dioxide in the air is absorbed, and oxygen is released by the plant.

Julius Robert Mayer: Mayer proposed the idea that light energy is being converted into chemical energy during photosynthesis.

Julius Von Sachs: He discovered that the photosynthesis process leads to the production of glucose molecules.

T.W.Engelmann: Engelmann was the scientist who discovered the importance of chlorophyll in photosynthesis.

Cornelius van Niel: He introduced the chemical equation of the photosynthesis process when he revealed that the oxygen released by plants at the end of photosynthesis comes from water and not from carbon dioxide.

Also Read:  Photosynthesis in Higher Plants

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Are any experiments that had been done but related to other factors which affecting the rate of photosynthesis?, If so then I would be grateful if you can send me any of them. I am very interested to do such experiment and that will be also a part of my assessment task that I will be doing next week. Most of the information that I get from the source really help me, and I hope that it is vital for me.

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Early Pioneers of Photosynthesis Research

• First Online: 01 January 2011

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• Jane F. Hill 4  

Part of the book series: Advances in Photosynthesis and Respiration ((AIPH,volume 34))

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Before the early researchers on plant nutrition worked out the fundamentals of photosynthesis, plants were believed to obtain their nutrients from humus in the soil. Then, over a period of about 200 years, a succession of investigators supplied pieces of the puzzle that eventually allowed formulation of the overall equation for photosynthesis. Jan van Helmont, in the early seventeenth century, concluded that plants are composed not of humus but of water that has been transmuted into plant substance. In the early eighteenth century, Stephen Hales found evidence that “air” was a component of the plant body. The involvement of water and air remained conjectural, however, until the late eighteenth century, when the new chemical theories of Antoine Lavoisier allowed the understanding of plant nutrition to advance. Joseph Priestley found that plants and animals are interdependent through their complementary effects on the atmosphere, and his discovery of oxygen was important for Lavoisier’s formulation of the new chemistry. Jan Ingen-Housz discovered that plants need light in order to release oxygen and that the green color of plants is important. Jean Senebier showed that carbon dioxide is also essential. Nicholas de Saussure, with his embrace of the new chemical concepts and his well-targeted experiments, was able to assemble a more comprehensive picture of plant nutrition, encompassing carbon dioxide from the atmosphere, water and mineral nutrients from the soil, and light from the sun. In the mid-nineteenth century, Robert Mayer completed the outline of the overall scheme with his insight that photosynthesizing plants convert light energy into chemical energy. Some of the important eighteenth-century photosynthesis pioneers were overshadowed by the drama of the profound changes shaking chemistry and are less well known than they should be. Some of their discoveries are misattributed or misstated in the literature, even down to the present day.

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Acknowledgements

I thank Govindjee for inviting me to write this chapter and for advice, guidance, and assistance. I also thank Kärin Nickelsen and Ekkehard Höxtermann for helpful comments on a draft of the manuscript. In addition, I thank my husband, William A. Hill, for editing assistance, and the staffs of the National Library of Medicine, and of Archives and Special Collections, Dickinson College, Carlisle, Pennsylvania, for help with research.

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Hill, J.F. (2012). Early Pioneers of Photosynthesis Research. In: Eaton-Rye, J., Tripathy, B., Sharkey, T. (eds) Photosynthesis. Advances in Photosynthesis and Respiration, vol 34. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-1579-0_30

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Early Evolution of Photosynthesis 1

Photosynthesis is the only significant solar energy storage process on Earth and is the source of all of our food and most of our energy resources. An understanding of the origin and evolution of photosynthesis is therefore of substantial interest, as it may help to explain inefficiencies in the process and point the way to attempts to improve various aspects for agricultural and energy applications.

A wealth of evidence indicates that photosynthesis is an ancient process that originated not long after the origin of life and has evolved via a complex path to produce the distribution of types of photosynthetic organisms and metabolisms that are found today ( Blankenship, 2002 ; Björn and Govindjee, 2009 ). Figure 1 shows an evolutionary tree of life based on small-subunit rRNA analysis. Of the three domains of life, Bacteria, Archaea, and Eukarya, chlorophyll-based photosynthesis has only been found in the bacterial and eukaryotic domains. The ability to do photosynthesis is widely distributed throughout the bacterial domain in six different phyla, with no apparent pattern of evolution. Photosynthetic phyla include the cyanobacteria, proteobacteria (purple bacteria), green sulfur bacteria (GSB), firmicutes (heliobacteria), filamentous anoxygenic phototrophs (FAPs, also often called the green nonsulfur bacteria), and acidobacteria ( Raymond, 2008 ). In some cases (cyanobacteria and GSB), essentially all members of the phylum are phototrop2hic, while in the others, in particular the proteobacteria, the vast majority of species are not phototrophic.

Small subunit rRNA evolutionary tree of life. Taxa that contain photosynthetic representatives are highlighted in color, with green highlighting indicating a type I RC, while purple highlighting indicates a type II RC. The red arrow indicates the endosymbiotic event that formed eukaryotic chloroplasts. Tree adapted from Pace (1997) .

Overwhelming evidence indicates that eukaryotic photosynthesis originated from endosymbiosis of cyanobacterial-like organisms, which ultimately became chloroplasts ( Margulis, 1992 ). So the evolutionary origin of photosynthesis is to be found in the bacterial domain. Significant evidence indicates that the current distribution of photosynthesis in bacteria is the result of substantial amounts of horizontal gene transfer, which has shuffled the genetic information that codes for various parts of the photosynthetic apparatus, so that no one simple branching diagram can accurately represent the evolution of photosynthesis ( Raymond et al., 2002 ). However, there are some patterns that can be discerned from detailed analysis of the various parts of the photosynthetic apparatus, so some conclusions can be drawn. In addition, the recent explosive growth of available genomic data on all types of photosynthetic organisms promises to permit substantially more progress in unraveling this complex evolutionary process.

While we often talk about the evolution of photosynthesis as if it were a concerted process, it is more useful to consider the evolution of various photosynthetic subsystems, which have clearly had distinct evolutionary trajectories. In this brief review we will discuss the evolution of photosynthetic pigments, reaction centers (RCs), light-harvesting (LH) antenna systems, electron transport pathways, and carbon fixation pathways. These subsystems clearly interact with each other, for example both the RCs and antenna systems utilize pigments, and the electron transport chains interact with both the RCs and the carbon fixation pathways. However, to a significant degree they can be considered as modules that can be analyzed individually.

ORIGINS OF PHOTOSYNTHESIS

We know very little about the earliest origins of photosynthesis. There have been numerous suggestions as to where and how the process originated, but there is no direct evidence to support any of the possible origins ( Olson and Blankenship, 2004 ). There is suggestive evidence that photosynthetic organisms were present approximately 3.2 to 3.5 billion years ago, in the form of stromatolites, layered structures similar to forms that are produced by some modern cyanobacteria, as well as numerous microfossils that have been interpreted as arising from phototrophs ( Des Marais, 2000 ). In all these cases, phototrophs are not certain to have been the source of the fossils, but are inferred from the morphology or geological context. There is also isotopic evidence for autotrophic carbon fixation at 3.7 to 3.8 billion years ago, although there is nothing that indicates that these organisms were photosynthetic. All of these claims for early photosynthesis are highly controversial and have engendered a great deal of spirited discussion in the literature ( Buick, 2008 ). Evidence for the timing of the origin of oxygenic photosynthesis and the rise of oxygen in the atmosphere is discussed below. The accumulated evidence suggests that photosynthesis began early in Earth’s history, but was probably not one of the earliest metabolisms and that the earliest forms of photosynthesis were anoxygenic, with oxygenic forms arising significantly later.

PHOTOSYNTHETIC PIGMENTS

Chlorophylls are essential pigments for all phototrophic organisms. Chlorophylls are themselves the product of a long evolutionary development, and can possibly be used to help understand the evolution of other aspects of photosynthesis. Chlorophyll biosynthesis is a complex pathway with 17 or more steps ( Beale, 1999 ). The early part of the pathway is identical to heme biosynthesis in almost all steps and has clearly been recruited from that older pathway. The later steps include the insertion of magnesium and the elaboration of the ring system and its substituents. The earliest version of the pathway (and that used by most modern anoxygenic photosynthetic organisms) almost certainly was anaerobic, both not requiring and not tolerating the presence of O 2 . However, all modern oxygenic photosynthetic organisms now require O 2 as an oxidant at several steps in the pathway. This has been explained in terms of gene replacement of the genes coding for the enzymes at these steps, with the result that the overall pathway is unchanged but the enzymes at key steps are completely different in different groups of phototrophs ( Raymond and Blankenship, 2004 ).

A key concept in using chlorophyll biosynthesis pathways to infer the evolution of photosynthesis is the Granick hypothesis, which states that the biosynthetic pathway of chlorophyll recapitulates the evolutionary sequence ( Granick, 1965 ). This is an appealing idea and probably at least partly true. However, in some cases, in particular the situation of chlorophyll and bacteriochlorophyll, it has been argued that the strict version of the Granick hypothesis is misleading and other interpretations are more likely ( Blankenship, 2002 ; Blankenship et al., 2007 ).

All photosynthetic organisms contain carotenoids, which are essential for photoprotection, usually also function as accessory pigments, and in many cases serve as key regulatory molecules. Carotenoids, unlike chlorophylls, are also found in many other types of organisms, so their evolutionary history may reflect many other functions in addition to photosynthesis ( Sandman, 2009 ).

REACTION CENTERS

The RC complex is at the heart of photosynthesis; so much attention has been paid to understand the evolution of RCs. A wealth of evidence, including structural, spectroscopic, thermodynamic, and molecular sequence analysis, clearly segregates all known RCs into two types of complexes, called type I and type II ( Blankenship, 2002 ). Anoxygenic phototrophs have just one type, either type I or II, while all oxygenic phototrophs have one of each type. The primary distinguishing feature of the two types of RCs are the early electron acceptor cofactors, which are FeS centers in type I RCs and pheophytin/quinone complexes in type II RCs. The distribution of RC types on the tree of life is shown in Figure 1 and a comparative electron transport diagram that compares the different RCs in different types of organisms is shown in Figure 2 , with type I RCs color coded green and type II RCs color coded purple.

Electron transport diagram indicating the types or RCs and electron transport pathways found in different groups of photosynthetic organisms. The color coding is the same as for Figure 1 and highlights the electron acceptor portion of the RC. Figure courtesy of Martin Hohmann-Marriott.

Further analysis strongly suggests that all RCs have evolved from a single common ancestor and have a similar protein and cofactor structure. This is clearly seen when structural overlays of both type I and II RCs are made, showing a remarkably conserved three-dimensional protein and cofactor structure, despite only minimal residual sequence identity ( Sadekar et al., 2006 ). These comparisons have been used to derive structure-based evolutionary trees that do not rely on sequence alignments. Figure 3 shows a schematic evolutionary tree of RCs that is derived from this sort of analysis. It proposes that the earliest RC was intermediate between type I and II (type 1.5) and that multiple gene duplications have given rise to the heterodimeric (two related yet distinct proteins that form the core of the RC) complexes that are found in most modern RCs.

Schematic evolutionary tree showing the development of the different types of RC complexes in different types of photosynthetic organisms. This tree is based on structural comparisons of RCs by Sadekar et al. (2006) . Blue color coding indicates protein homodimer, while red indicates protein heterodimer complexes. Red stars indicate gene duplication events that led to heterodimeric RCs. Helio, Heliobacteria; GSB, green sulfur bacteria; FAP, filamentous anoxygenic phototroph.

A second important issue that relates to RC evolution is the question of how both type I and II RCs came to be in cyanobacteria, while all other photosynthetic prokaryotes have only a single RC. The various proposals that have been made to explain this fact can all be divided into either fusion or selective loss scenarios or variants thereof ( Blankenship et al., 2007 ). In the fusion hypothesis, the two types of RCs develop separately in anoxygenic photosynthetic bacteria and are then brought together by a fusion of two organisms, which subsequently developed the ability to oxidize water. In the selective loss hypothesis, the two types of RCs both evolved in an ancestral organism and then loss of one or the other RC gave rise to the organisms with just one RC, while the ability to oxidize water was added later. Both scenarios have proponents, and it is not yet possible to choose between them.

ELECTRON TRANSPORT CHAINS

The primary photochemistry and several of the early secondary electron transfer reactions take place within the RC complex. However, additional electron transfer processes are necessary before the process of energy storage is complete. These include the cytochrome bc 1 and b 6 f complexes. These complexes oxidize quinols produced by photochemistry in type II RCs or via cyclic processes in type I RCs and pumps protons across the membrane that in turn contribute to the proton motive force that is used to make ATP. All phototrophic organisms have a cytochrome bc 1 or b 6 f complex of generally similar architecture, with the exception of the FAP phylum of anoxygenic phototrophs ( Yanyushin et al., 2005 ). This group contains instead a completely different type of complex that is called alternative complex III. The evolutionary origin of this complex is not yet clear. While the cytochrome bc 1 and b 6 f complexes are similar in many ways, the cytochrome c 1 and f subunits are very different and are almost certainly of distinct evolutionary origin ( Baniulis et al., 2008 ).

ANTENNA SYSTEMS

All photosynthetic organisms contain a light-gathering antenna system, which functions to collect excitations and transfer them to the RC where the excited state energy is used to drive photochemistry ( Green and Parson, 2003 ). While the presence of an antenna is universal, the structure of the antenna complexes and even the types of pigments used in them is remarkably varied in different types of photosynthetic organisms. This very strongly suggests that the antenna complexes have been invented multiple times during the course of evolution to adapt organisms to particular photic environments. So while evolutionary relationships are clear among some categories of antennas, such as the LH1 and LH2 complexes of purple bacteria and the LHCI and LHCII complexes of eukaryotic chloroplasts, it is not possible to relate these broad categories of antennas to each other in any meaningful way. This is in contrast to the RCs, where all available evidence clearly points to a single origin that has subsequently undergone a complex evolutionary development.

CARBON FIXATION PATHWAYS

Most phototrophic organisms are capable of photoautotrophic metabolism, in which inorganic substrates such as water, H 2 S, CO 2 , or HCO 3 − are utilized along with light energy to produce organic carbon compounds and oxidized donor species. However, there are some groups of phototrophs that cannot carry out photoautotrophic metabolism and there are at least three entirely separate autotrophic carbon fixation pathways that are found in different types of organisms ( Thauer, 2007 ). By far the dominant carbon fixation pathway is the Calvin-Benson cycle, which is found in all oxygenic photosynthetic organisms, and also in most purple bacteria. The GSB use the reverse tricarboxylic acid cycle, and many of the FAPs use the 3-hydroxypropionate cycle ( Zarzycki et al., 2009 ). The Gram-positive heliobacteria lack any known autotrophic carbon fixation pathway and usually grow photoheterotrophically ( Asao and Madigan, 2010 ). Similarly, the aerobic anoxygenic phototrophs, which are closely related to the purple bacteria, lack any apparent ability to fix inorganic carbon. In the latter case, it seems most likely that the ancestor of this group contained the Calvin-Benson cycle but lost the genes because of their obligate aerobic lifestyle ( Swingley et al., 2007 ).

The carbon fixation machinery is thus similar to the antennas, in that several entirely separate solutions have been adopted by different classes of phototrophic organisms. This would be consistent with the idea that the earliest phototrophs were photoheterotrophic, using light to assimilate organic carbon, instead of being photoautotrophic. The ability to fix inorganic carbon was then added to the metabolism somewhat later during the course of evolution, possibly borrowing carbon fixation pathways that had developed earlier in autotrophic nonphotosynthetic organisms.

TRANSITION TO OXYGENIC PHOTOSYNTHESIS

Perhaps the most widely discussed yet poorly understood event in the evolution of photosynthesis is the invention of the ability to use water as an electron donor, producing O 2 as a waste product and giving rise to what is now called oxygenic photosynthesis. The production of O 2 and its subsequent accumulation in the atmosphere forever changed the Earth and permitted the development of advanced life that utilized the O 2 during aerobic respiration. Several lines of geochemical evidence indicate that free O 2 began to accumulate in the atmosphere by 2.4 billion years ago, although the ability to do oxygenic photosynthesis probably began somewhat earlier ( Buick, 2008 ). In order for O 2 to accumulate, it is necessary that both the biological machinery needed to produce it has evolved, but also the reduced carbon produced must be buried by geological processes, which are controlled by geological processes such as plate tectonics and the buildup of continents. So the buildup of O 2 in the atmosphere represents a coming together of the biology that gives rise to O 2 production and the geology that permits O 2 to accumulate.

Oxygen is produced by PSII in the oxygen evolving center, which contains a tetranuclear manganese complex. The evolutionary origin of the oxygen evolving center has long been a mystery. Several sources have been suggested, but so far no convincing evidence has been found to resolve this issue ( Raymond and Blankenship, 2008 ). The possibility that functional intermediate stages existed that connect the anoxygenic type II RCs to PSII seems likely ( Blankenship and Hartman, 1998 ).

The process of photosynthesis originated early in Earth’s history, and has evolved to its current mechanistic diversity and phylogenetic distribution by a complex, nonlinear process. Current evidence suggests that the earliest photosynthetic organisms were anoxygenic, that all photosynthetic RCs have been derived from a single source, and that antenna systems and carbon fixation pathways have been invented multiple times.

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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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• BCcampus Open Publishing - Concepts of Biology – 1st Canadian Edition - Overview of Photosynthesis
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• Table Of Contents

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

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

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

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

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

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

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

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

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

General characteristics

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

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

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

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

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

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Early Experiments to Understand Photosynthesis: Historical Account of Photosynthesis

Early Experiments to Understand Photosynthesis: Have you heard the term photosynthesis? Have you ever wondered how we came to know that plants require sunlight or water for photosynthesis? Let us understand all these facts. Only photosynthesis is the means by which certain organisms can make their own organic food from inorganic raw material with the help of solar energy. The organisms performing photosynthesis are therefore called autotrophs. The study on photosynthesis started around 300 years ago. Simple experiments have shown that chlorophyll (green pigment of the leaf), light, and CO 2 are required for photosynthesis to occur.

Photosynthesis

Photosynthesis is the process of the plant by which they utilize sunlight, water (H₂O), carbon dioxide (CO₂), and chlorophyll molecules to form oxygen and glucose (C₆H₁₂O₆) molecules. It converts light energy into chemical energy. Let us study the various historical experiments of photosynthesis.

Learn Everything About Photosynthesis Here

Historical Account of Experiments on Photosynthesis

There have been several simple experiments done that led to a gradual development in our understanding of photosynthesis

i. Joseph Priestley (1733-1804):  In 1770, Priestly revealed the essential role of air in the growth of green plants through several experiments. He discovered oxygen in 1774. In an experiment done, Priestley observed that a candle is burning in a closed space, i.e., a bell jar, soon gets extinguished. Similarly, a mouse would die of suffocation in a closed space due to the unavailability of oxygen. Through his experiments, he concluded that both the burning candle and the mouse contaminates the air they use. But, when a mint plant was placed in the same bell jar, the mouse stayed alive, and the candle continued to burn. As a result, Priestley concluded that plants add to the air what a breathing mouse and burning candle remove or use.

ii. Jan Ingenhousz (1730-1799): Ingenhousz, through his experiments, showed that sunlight is essential for the plant process that helps to somehow purify the air fouled by the breathing of mice and the burning candle. In another experiment with an aquatic plant ( Hydrilla ), he showed that small bubbles were formed around the green parts of the plant in bright sunlight. While in the dark, no bubbles were formed. He identified those bubbles to be oxygen. Therefore,  he showed that in the presence of sunlight, only the green parts of the plants could release oxygen.

iii. Julius von Sachs (1854): He found that the green parts in plants are the place where glucose is made, and glucose is usually stored as starch. Later, he showed that the green substance in plants (now called chlorophyll) is located in special bodies (now called chloroplasts) within the plant cells. 

iv. T.W. Engelmann (1843-1909): He experimented on Cladophora using a prism; he split light into its spectral components and then illuminated a green alga kept with aerobic bacteria. The bacteria were used to detect the sites of oxygen evolution. He found that the bacteria accumulated mainly in the blue and red light regions of the split spectrum. And thus, the first action spectrum of photosynthesis was described. The empirical equation representing the total process of photosynthesis for organisms evolving oxygen was understood as

v. Cornelius van Niel (1897-1985): Van Neil, based on his studies of purple and green sulphur bacteria, demonstrated that during photosynthesis, oxygen evolved by the green plants comes from water and not from carbon dioxide. The hypothesis was later proved by using radioisotopic techniques.

Where H 2 A is the oxidisable compound (H 2 O or H 2 S).

The correct equation to represent the overall process of photosynthesis could thus be summed as

Where C 6 H 12 O 6 is glucose and O 2 is released from water.

vi. Ruben, Kamen, and Hassid used a heavy, but non-radioactive, stable isotope of oxygen 18 O to prove that O 2 evolved during light reaction comes from H 2 O and not from CO 2 .

Some Important Experiments Related to Photosynthesis

Let us now study certain experiments to study the need for light, chlorophyll and carbon dioxide for photosynthesis.

Experiment to Demonstrate that Light and Chlorophyll is Necessary for Photosynthesis: 

Aim: To demonstrate the use of light and chlorophyll in photosynthesis.

Materials Required: Destarched leaf, Black strip, Iodine solution.

Procedure: 

• Take a destarched potted plant having variegated leaves and cover 2-3 leaves with black paper. 
• Expose the potted plant to sunlight for 1-2 hours. 
• Pluck one covered leaf and one exposed leaf.
• Both the leaves are then dipped in iodine solution. 

Observation: The leaf which was covered does not pass the starch test proving that in the absence of light, photosynthesis cannot occur. The exposed leaf to sunlight shows blue and black spots wherever chlorophyll is present to show a positive starch test.

Conclusion: Green parts of the leaf contain chlorophyll. Hence they carry out photosynthesis and produce starch which turns blue-black when tested with iodine. This experiment proves that sunlight and chloroplast are important for photosynthesis.

Experiment to Demonstrate that Carbon Dioxide is Necessary for Photosynthesis (Moll’s Half leaf experiment): 

Aim: To demonstrate the use of carbon dioxide in photosynthesis.

Materials Required: Potted plant, beaker, KOH solution.

• Take a potted plant and enclose a part of one leaf in a test tube.
• Fill this test tube with some KOH soaked cotton (which absorbs CO 2 ) while the other half of the leaf is exposed to air.
• Pluck the half-covered leaf after a few hours.
• Dip the leaf in iodine solution.

Conclusion: When the two halves of leaf were tested for starch, it was found that only the exposed part of the leaf tested positive for starch. This showed us that CO 2 is required for photosynthesis.

Photosynthesis is the process used by green plants to form glucose molecules by using water, carbon dioxide and chlorophyll molecules. Various scientists performed several experiments to prove the usage of light and carbon dioxide in the formation of food in plants. Scientists like Priestley and Ingenhousz proved that the plants in the presence of light release pure air (oxygen), which is later taken up by other organisms for the purpose of respiration. Later on, Engelmann performed several experiments to give the action spectrum of light and proved that the maximum photosynthesis occurs in the blue and red light of the visible spectrum.

Frequently Asked Questions (FAQs) on Early Experiments to Understand Photosynthesis

Q.1. Which plant was used by Ingenhousz? Ans: Ingenhousz used an aquatic plant Hydrilla to prove plants produce pure air.

Q.2. Which process involves the release of oxygen in plants? Ans: Oxygen is released in plants by the process of the photolysis of water.

Q.3. Which chemical solution was used in Moll’s half leaf experiment? Ans: KOH was used in Moll’s half leaf experiment to prove that carbon dioxide is necessary for photosynthesis purposes.

Q.4. Where does photosynthesis take place? Ans: Photosynthesis takes place in the green part of the plant, which contains chloroplast.

Q.5. Which plant was used by Engelmann to show the action spectrum of the light? Ans: Engelmann used Cladophora to show the action spectrum of light.

Study Mechanism Of Photosynthesis Here

We hope this detailed article on the Early Experiments to Understand Photosynthesis helps you in your preparation. If you get stuck do let us know in the comments section below and we will get back to you at the earliest.

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Early Experiments on Photosynthesis

Photosynthesis is a process by which plants produce their food. It is a photochemical process in which the light energy is absorbed by the plants and is converted into chemical energy to produce oxygen. This process was followed by the plants for ages. But it’s discovery and identification were done only in 1800 and several scientists conducted many different types of experiments to prove the existence of photosynthesis. 

Photosynthesis Discovery – Early Experiments

The process of photosynthesis is carried by some of the required raw materials like water, carbon dioxide, and cellular components like plastids. Plants make use of these raw materials to synthesize carbohydrates in the presence of sunlight. These key features of photosynthesis were revealed during the mid-nineteenth century.

Some of the experiments that were conducted by the early scientists to explore photosynthesis in a better way are - 

Experiment to Prove the Importance of Carbon Dioxide in Photosynthesis

Materials Required: A healthy potted plant, a wide-mouthed glass bottle with a split cork, potassium hydroxide solution (KOH), and starch solution.

Experiment:

Take a healthy potted plant and keep it in the darkroom for two to three days to ensure leaves are free from starch.

In a wide-mouthed glass bottle add 10-15 ml of potassium hydroxide solution and split the cork vertically.

Now minutely, insert half part of a leaf into a glass bottle through the split cork and the other half exposed to air.

Place the complete unit undisturbed in sunlight for about 3 – 4 hours.

Remove the leaf after 4 hours from the plant and slowly remove it out from the bottle and test it with the starch solution.

We can observe that the half part leaf which was inside the glass bottle (KOH solution) did not show any colour change but the other half part exposed to surroundings became dark brown indicating the presence of starch in it.

Conclusion: In this experiment, we can conclude that carbon dioxide is essential for photosynthesis. Both portions of leaf received the same amount of water, chloroplasts, and sunlight but the half part which was inside the glass bottle did not receive carbon dioxide. 

Later, many improvised experiments were conducted by scientists to analyze the essential components for photosynthesis. Joseph Priestley (1733-1804) was the first scientist amongst others to carry out these experiments.

Experiment by Joseph Priestley

After conducting a series of experiments in 1770, Joseph Priestley concluded that the essentiality of air for photosynthesis and also for the growth of plants.

Materials Required: A candle, rat, a bell jar, and a plant.

Firstly, a burning candle and a rat were kept together in the single bell jar.

After some time, the candle extinguished and the rat died.

For the second time, he kept a burning candle, rat, and a green plant all together in the bell jar.

He observed that neither the candle got extinguished, nor did the rat die.

Conclusion: Based on his observations, the scientist Priestley concluded that in the first case, the air in the bell jar got polluted by the candle and the existence of the rat. However, in the second case, the plant restored the air that was spoiled by the candle and the rat. But this function of the plants was not revealed quite soon by scientists. 

Other Experiments

Scientist Jan Ingenhousz also conducted experiments using the same set-up but the twist was the presence of sunlight that was highlighted as being an essential product for plants to refresh the air that was polluted by the candle or rat.

Jean Senebier came to a conclusion which said that plants absorb carbon dioxide and release oxygen during photosynthesis.

Julius Robert Mayer demonstrated that plants convert light energy into chemical energy.

Later, Julius von Sachs revealed that glucose was produced by plants.

T.W Engelmann discovered the role of chlorophylls and Cornelius van Niel uncovered that the release of oxygen by plants is from water (H 2 O), not from carbon dioxide. He also gave the general photosynthesis equation. 

An outline was drawn for the process of photosynthesis by scientists. They concluded that light is essential for photosynthesis, and plants use carbon dioxide and water for the preparation of glucose (carbohydrate), where water molecules are the hydrogen donors and oxygen (O 2 ) is the by-product of this biological process.

FAQs on Early Experiments on Photosynthesis

1. Define Photosynthesis

Photosynthesis is a process by which plants produce their food. It is a photochemical process in which the light energy is absorbed by the plants and is converted into chemical energy to produce oxygen. This process was followed by the plants for ages. But it’s discovery and identification were done only in 1800 and several scientists conducted many different types of experiments to prove the existence of photosynthesis.

2. What Were the Materials Used for the Experiment of Photosynthesis?

The materials used for the experiment of Photosynthesis was - 

A healthy potted plant

A wide-mouthed glass bottle with a split cork

Potassium hydroxide solution (KOH)

Starch solution

Biology • Class 11

Photosynthesis I: Harnessing the energy of the sun

by Nathan H Lents, Ph.D., John Nishan

Listen to this reading

Did you know that the oxygen we breathe is a waste product? Of photosynthesis, that is. Through this remarkable process, plants capture energy from sunlight and produce the sugars that provide sustenance to nearly every living thing on Earth along with the oxygen we need to survive.

Photosynthesis is a process by which an organism converts light energy from the sun into chemical energy for its sustenance.

Photosynthesis occurs in plants, algae, and some species of bacteria.

In plants, chloroplasts contain chlorophyll that absorbs light in the red and blue-violet regions of the spectrum.

Photosynthesis occurs in two stages: the light-dependent stage that occurs in the thylakoid membrane of the chloroplast and harvests solar energy, and the light-independent stage that takes that energy and makes sugar from carbon dioxide.

Before scientists understood the process of photosynthesis , they were at a loss to explain how plants could grow and increase their mass so dramatically from what appeared to be a steady diet of water. A 17th century Flemish chemist named Jean Baptista van Helmont thought plants “extracted” the bulk of their food from soil (Van Helmont, 1841). Other scientists assumed plants gained their weight and size from carbon dioxide, while others assumed that water alone gave plants their heft.

None of these explanations, however, held up when tested experimentally. In test after test, mass lost by soil , water, and even carbon dioxide didn’t measure up to the mass gained by a growing plant. It wasn’t until Joseph Priestley’s experiments a century later that scientists began to suspect sunlight as the major contributor to a plant’s growth.

• Early experiments towards the discovery of photosynthesis

Priestley, partially credited with the discovery of elemental oxygen, found that when he placed fresh sprigs of mint leaves inside a sealed glass container, a candle would burn longer than if the leaves were not there (Figure 1). He also found that a previously extinguished candle would reignite inside a sealed jar – sometimes days after it had ceased to burn – if mint leaves were present. This caused him to suspect that the leaves were somehow “refreshing” the air inside the container.

Figure 1: Priestley’s experiments suggested leaves “refreshed” the air inside a closed container.

Several years later, a Dutch scientist named Jan Ingenhousz, having heard of Priestley’s experiments , began to conduct experiments of his own. He submerged willow plants in water and saw that bubbles formed on the surface of the leaves. The bubbles, however, formed only when the experiment was conducted in the presence of sunlight. Ingenhousz later determined the gas bubbles were oxygen, but never fully understood the significance of what he had observed regarding the sunlight.

• Putting it all together: Reactants and products of photosynthesis

Collectively, these chemists established the products and reactants of photosynthesis – water, oxygen, carbon dioxide, and light . But it took the musings of a German physicist named Julius Von Mayer to put the pieces together. Von Mayer, the first to propose that “energy is neither created nor destroyed,” was also first to suggest that plants derive their energy for growth from sunlight.

Von Mayer’s understanding of photosynthesis implied that the sun was the basis for all life on Earth. The sun’s chemical energy , he said, feeds the plants that in turn feed almost every living thing on the planet. He explained photosynthesis as a process that created organic molecules – sugars – from the inorganic molecules carbon dioxide and water (Liebig, 1841). He first articulated the equation as:

CO 2 + H 2 O + light energy → O 2 + organic matter + chemical energy

Work by other scientists helped to establish the chemical formula of the organic products of photosynthesis , which is usually simplified as a glucose molecule: C 6 H 12 O 6 . The properly balanced general formula for photosynthesis thus becomes:

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

Comprehension Checkpoint

• The energy of photosynthesis comes from light

The principal product of photosynthesis (sugar) is a high-energy molecule , but the reactants (carbon dioxide and water), are low-energy molecules, so the process of photosynthesis needs an energy source to drive it. Molecules called pigments absorb energy from light . The main pigment in photosynthesis is called chlorophyll . Chlorophyll exists in several different forms in different organisms . Chlorophyll a is the main photosynthetic pigment found in land plants and algae . It absorbs light in the blue/violet range of the light spectrum (wavelengths of 400-450nm) as you can see in Figure 2. It also absorbs light in the red range of the spectrum (wavelengths of 650-700nm) to a lesser degree. Green light is almost completely reflected by chlorophyll, giving plants their greenish hue.

Figure 2: The absorption spectrum of chlorophyll a and b.

Plants do not make equal use of all the wavelengths present in the full range of visible light – a fact first demonstrated by German plant physiologist T. W. Engelmann in 1882. He used a simple experiment to demonstrate that the blue and red wavelengths of light, in particular, were the biggest drivers of photosynthesis .

• The action spectrum of photosynthesis

Engelmann split white light into its spectral components using a prism and shone it on a dish of liquid solution containing a photosynthetic green algae called Chladophora . He then released bacteria into the solution. The bacteria, which need oxygen to survive, migrated toward those areas in the dish where blue and red wavelength light was shining. Why? Because where the red and blue range of light was shining, the photosynthetic algae produced more oxygen due to increased photosynthetic activity. With this demonstration, Engelmann had established the first action spectrum of photosynthesis .

Chlorophyll a does not perfectly overlap with the action spectrum of photosynthesis identified by Engelmann (see Table 1). This led scientists to suspect that there are additional pigments in plants that absorb light at different wavelengths . Land plants have pigments such as chlorophyll b and carotene, while other photosynthetic organisms , like protists, have chlorophyll c and chlorophyll a .

Plant pigments are classified as either chlorophylls or carotenoids. Chlorophylls reflect green light while carotenoids reflect light in the red, orange, and yellow range. Carotenoids give carrots their color. They are considered an accessory pigment because they cannot transfer sunlight energy directly to the photosynthetic pathway. Carotenoids pass their absorbed energy to chlorophyll, which in turn transfers energy to the photosynthetic pathway.

Photosynthetic pigments are large, hydrophobic molecules embedded in protein pigment complexes called photosystems that work like antennas to collect the sun’s energy . In plants, the photosystems are embedded in the thylakoid membranes inside chloroplasts (Figure 3).

Figure 3: Chlorophyll pigments are found in thylakoid membranes inside plant cell organelles called chloroplasts.

• Phase One: The light-dependent reactions

Photosynthesis occurs in two phases: the light-dependent reactions and the Calvin-Benson Cycle (see the Photosynthesis I video below). The light-dependent reaction is the first phase, when pigments like chlorophyll harvest light energy . The Calvin-Benson Cycle uses that energy to synthesize high-energy sugar molecules from carbon dioxide. In plants and algae , the light reactions occur within the thylakoid membranes of chloroplasts . The animation below provides an overview of photosynthesis.

Photosynthesis 1

When a photon of light (see Light I: Particle or Wave? module) strikes a pigment molecule , its energy is transferred to the pigment and one of the pigment’s electrons becomes “excited.” When excitation of an electron occurs, it “jumps” to a higher energy state. Thus, the energy of light is “captured” by the pigment in the form of an excited electron. The excited electron can hold on to this energy only for a brief time, though. If it cannot pass the energy quickly, the electron will fall back down to a low-energy state and the energy will be given off as heat .

Within a chloroplast of a leaf, however, there are many pigment molecules packed together very tightly in structures called light-harvesting complexes, which are combinations of proteins , cofactors, and pigment molecules. The pigment molecules are constantly moving in random, Brownian motion , colliding with one another. Excited pigments transfer energy to their neighboring pigments until it reaches the reaction center, as shown in Figure 4.

Figure 4: Electron excitement and energy transfer inside a light-harvesting complex.

Like the light-harvesting complexes, the reaction centers are also made of proteins , cofactors, and pigments , but there are two types of reaction centers: photosystem I and photosystem II. Photosystem I, so named because it was discovered first, is also referred to as P700 because the special chlorophyll a pigment molecules that form it best absorb light of wavelength 700nm. Photosystem II is also referred to as P680, because the chlorophyll molecules that form it best absorb light in the 680nm wavelength. In both cases, after either P700 or P680 become excited, either by a photon or another excited pigment molecule, one of its electrons moves to a higher energy state. The difference between these two photosystems lies in what happens next with this harnessed energy. View a video of photosystems I and II below.

Photosynthesis 2

• Photosystem II

Even though it was discovered and named second, photosystem II is actually where the story begins. When a photon of light strikes the reaction center of photosystem II, it excites an electron that leaves and begins its journey through a series of high-energy electron acceptors and donors collectively known as the electron transport chain (ETC) as shown in Figure 5. (This particular ETC is called the cytochrome ETC, after one of the members of the chain that was discovered first.)

Figure 5: Photosystem II initiates the electron transport chain and primes the proton pump for ATP synthesis.

At the same time, two water molecules bind to a water-splitting enzyme at the reaction center of photosystem II, as seen in Figure 6. When the water molecules split, ionized hydrogen atoms (H + ) enter the thylakoid space. An enzyme called cytochrome b6f, the next stop in the chain after photosystem II, generates more ions for the proton pump and sends the excited electrons along toward photosystem I. As the hydrogen ions accumulate within the thylakoid space, they create the H + gradient that drives ATP synthesis . ATP will be used for sugar synthesis later, in the Calvin-Benson Cycle.

Figure 6: Formation of O 2 by photosystem II.

Oxygen atoms from the split water molecules also accumulate within the thylakoid space. Lone oxygen atoms are very reactive and rapidly combine to form molecular oxygen (O 2 ) that is released as a waste product of photosynthesis . Yes, each molecule of oxygen that we breathe was formed in a chloroplast somewhere as an accidental by-product of the splitting of water. Electrons are at a much lower energy state at the end of the ETC than they were at the beginning of the process . They get a badly needed boost at the reaction centers in photosystem I.

• Photosystem I

Photosystem I also consists of light-harvesting complexes with lots of pigment molecules for capturing light energy . Light energy harvested from photons and intermediate-energy electrons from photosystem II flow to a special chlorophyll a molecule structure called P700 in photosystem I. Electrons jump up to a high-energy state when a photon arrives at P700, either directly from sunlight, or through a collision with an already excited pigment.

Once re-excited to a high energy level, the electrons don’t stay for long. Excited electrons leave photosystem I and flow through another ETC, but this one, called the Ferredoxin ETC, is much shorter and does not drive ATP synthesis . The Ferredoxin ETC passes the excited electrons to the high-energy electron acceptor NADP + , which then combines with a proton (H + ) from the surrounding solution and forms NADPH. NADPH then delivers high-energy electrons to the Calvin Cycle for long-term energy storage in the form of sugar (Figure 7).

Figure 7: Photosynthesis proteins embedded in a thylakoid membrane deliver high energy electrons to the Calvin Cycle and send hydrogen ions into the lumen to generate a proton gradient.

• Phase Two: The Calvin-Benson Cycle

After the energy of light is harvested as high-energy electrons held by NADPH, these electrons are then used to synthesize high-energy sugar molecules from the low-energy starting material of carbon dioxide. The Calvin-Benson Cycle used to be called “the dark reactions” because light is not directly involved. However, this name is misleading because the products of the light reactions are required to drive the Calvin Cycle. Thus, light is required, just not directly.

So far, we’ve seen how the flow of electrons in the light reactions goes like this (note: PSI and PSII stand for photosystem I and II):

This linear path is called noncyclic electron transport. However, not all electrons flow in this linear path. Some electrons double back and return to PSII after the PSI. This is called cyclic electron flow .

Why would some electrons take the redundant path of twice being energized by PSII and twice flowing through the cytochrome ETC? The answer is found when thinking about what the ETC produces – ATP . The simple noncyclic flow of electrons produces ATP and NADPH in roughly equal amounts. However, the Calvin Cycle needs more ATP than NADPH. Thus, the extra trip through the ETC that occurs in cyclic electron flow provides a little “boost” of ATP so that the Calvin Cycle has what it needs to synthesize sugars .

In roughly 300 years, our understanding of photosynthesis has progressed from mere identification of all the basic products and reactants of photosynthesis to a detailed picture of the molecular processes involved. We have summarized in this module how electrons are harvested, energized, and stored in the covalent bonds of NADPH, a process called light reactions . In the next module, we explore the Calvin-Benson Cycle where high-energy electrons from NADPH drive synthesis of carbohydrates – the sugars that provide sustenance to nearly every living thing on the Earth.

Table of Contents

Activate glossary term highlighting to easily identify key terms within the module. Once highlighted, you can click on these terms to view their definitions.

Activate NGSS annotations to easily identify NGSS standards within the module. Once highlighted, you can click on them to view these standards.

3 minute read

Photosynthesis

History of research.

People have long been interested in how plants obtain the nutrients they use for growth. The early Greek philosophers believed that plants obtained all of their nutrients from the soil . This was a common belief for many centuries.

In the first half of the seventeenth century, Jan Baptista van Helmont (1579-1644), a Dutch physician, chemist, and alchemist, performed important experiments which disproved this early view of photosynthesis. He grew a willow tree weighing 5 lb (2.5 kg) in a clay pot which had 200 lb (91 kg) of soil. Five years later, after watering his willow tree as needed, it weighed about 169 lb (76.5 kg) even though the soil in the pot lost only 2 oz (56 g) in weight. Van Helmont concluded that the tree gained weight from the water he added to the soil, and not from the soil itself. Although van Helmont did not understand the role of sunlight and atmospheric gases in plant growth, his early experiment advanced our understanding of photosynthesis.

In 1771, the noted English chemist Joseph Priestley performed a series of important experiments which implicated atmospheric gases in plant growth. Priestley and his contemporaries believed a noxious substance, which they called phlogiston , was released into the air when a flame burned. When Priestley burned a candle within an enclosed container until the flame went out, he found that a mouse could not survive in the "phlogistated" air of the container. However, when he placed a sprig of mint in the container after the flame had gone out, he found that a mouse could survive. Priestley concluded that the sprig of mint chemically altered the air by removing the "phlogiston." Shortly after Priestly's experiments, Dutch physician Jan Ingenhousz (1730-1799) demonstrated that plants "dephlogistate" the air only in sunlight, and not in darkness. Further, Ingenhousz demonstrated that the green parts of plants are necessary for" dephlogistation" and that sunlight by itself is ineffective.

As Ingenhousz was performing his experiments, the celebrated French chemist Antoine Lavoisier (1743-1794) disproved the phlogiston theory. He conclusively demonstrated that candles and animals both consume a gas in the air which he named oxygen. This implied that the plants in Priestley's and Ingenhousz's experiments produced oxygen when illuminated by sunlight. Considered by many as the founder of modern chemistry , Lavoisier was condemned to death and beheaded during the French revolution.

Lavoisier's experiments stimulated Ingenhousz to reinterpret his earlier studies of "dephlogistation." Following Lavoisier, Ingenhousz hypothesized that plants use sunlight to split carbon dioxide (CO 2 ) and use its carbon (C) for growth while expelling its oxygen (O 2 ) as waste. This model of photosynthesis was an improvement over Priestley's, but was not entirely accurate.

Ingenhousz's hypothesis that photosynthesis produces oxygen by splitting carbon dioxide was refuted about 150 years later by the Dutch-born microbiologist Cornelius van Niel (1897-1985) in America. Van Niel studied photosynthesis in anaerobic bacteria, rather than in higher plants. Like higher plants, these bacteria make carbohydrates during photosynthesis. Unlike plants, they do not produce oxygen during photosynthesis and they use bacteriochlorophyll rather than chlorophyll as a photosynthetic pigment. Van Niel found that all species of photosynthetic bacteria which he studied required an oxidizable substrate. For example, the purple sulfur bacteria use hydrogen sulfide as an oxidizable substrate and the overall equation for photosynthesis in these bacteria is:

On the basis of his studies with photosynthetic bacteria, van Niel proposed that the oxygen which plants produce during photosynthesis is derived from water, not from carbon dioxide. In the following years, this hypothesis has proven true. Van Niel's brilliant insight was a major contribution to our modern understanding of photosynthesis.

The study of photosynthesis is currently a very active area of research in biology . Hartmut Michel and Johann Deisenhofer recently made a very important contribution to our understanding of photosynthesis. They made crystals of the photosynthetic reaction center from Rhodopseudomonas viridis , an anaerobic photosynthetic bacterium, and then used x-ray crystallography to determine its three-dimensional structure. In 1988, they shared the Nobel Prize in Chemistry with Robert Huber for this ground-breaking research.

Modern plant physiologists commonly think of photosynthesis as consisting of two separate series of interconnected biochemical reactions, the light reactions and the dark reactions. The light reactions use the light energy absorbed by chlorophyll to synthesize labile high energy molecules. The dark reactions use these labile high energy molecules to synthesize carbohydrates, a stable form of chemical energy which can be stored by plants. Although the dark reactions do not require light, they often occur in the light because they are dependent upon the light reactions. In higher plants and algae, the light and dark reactions of photosynthesis occur in chloroplasts, specialized chlorophyll-containing intracellular structures which are enclosed by double membranes.

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Science Encyclopedia Science & Philosophy: Philosophy of Mind - Early Ideas to Planck length Photosynthesis - History Of Research, Location Of Light Reactions, Cam Photosynthesis, Photorespiration, Cyanobacteria, Anaerobic Photosynthetic Bacteria - Light reactions, Dark reactions, Photosynthesis in lower organisms, Chloroxybacteria

- Famous Historic Experiments Is water the source of energy in plants, the interaction of plants with air. Plants and Light External links. Provides a clear, concise and vivid account of the process of photosynthesis. Discusses the details of photosynthetic processes at the macro and molecular level Aimed at undergraduate and beginning graduate students, the text begins with a review of the principles of energy storage. Other topics include evolution, electron transfer pathways, kinetics, and genetic manipulations. The text is accompanied throughout by detailed diagrams. The purpose of the first part of this book is to describe and explain the behavior of light in natural waters The authors question whether photosynthetic adaptations take place primarily at the metabolic and biochemical level or through changes in structure and form, or both. In the interest of genetic engineering and agricultural applications, the authors analyze the relative importance of genes that control both metabolic and light reactions as well as the structure, arrangement, and orientation of photosynthesis. Search Menu Sign in through your institution Advance Articles Collections Focus Collections Browse by cover High-Impact Research Founders' Reviews Author Guidelines Quick and Simple Author Support Focus Issues Call for Papers Submission Site Open Access Options Self-Archiving Policy Why Publish with Us? About Plant Physiology Editorial Board Advertising & Corporate Services Journals on Oxford Academic Books on Oxford Academic Article Contents Origins of photosynthesis, photosynthetic pigments, reaction centers, electron transport chains, antenna systems, carbon fixation pathways, transition to oxygenic photosynthesis, literature cited. < Previous Early Evolution of Photosynthesis This work was supported by the Exobiology Program from the U.S. National Aeronautics and Space Administration (grant no. NNX08AP62G). E-mail [email protected] . www.plantphysiol.org/cgi/doi/10.1104/pp.110.161687 Article contents Figures & tables Supplementary Data Robert E. Blankenship, Early Evolution of Photosynthesis, Plant Physiology , Volume 154, Issue 2, October 2010, Pages 434–438, https://doi.org/10.1104/pp.110.161687 Permissions Icon Permissions Photosynthesis is the only significant solar energy storage process on Earth and is the source of all of our food and most of our energy resources. An understanding of the origin and evolution of photosynthesis is therefore of substantial interest, as it may help to explain inefficiencies in the process and point the way to attempts to improve various aspects for agricultural and energy applications. A wealth of evidence indicates that photosynthesis is an ancient process that originated not long after the origin of life and has evolved via a complex path to produce the distribution of types of photosynthetic organisms and metabolisms that are found today ( Blankenship, 2002 ; Björn and Govindjee, 2009 ). Figure 1 shows an evolutionary tree of life based on small-subunit rRNA analysis. Of the three domains of life, Bacteria, Archaea, and Eukarya, chlorophyll-based photosynthesis has only been found in the bacterial and eukaryotic domains. The ability to do photosynthesis is widely distributed throughout the bacterial domain in six different phyla, with no apparent pattern of evolution. Photosynthetic phyla include the cyanobacteria, proteobacteria (purple bacteria), green sulfur bacteria (GSB), firmicutes (heliobacteria), filamentous anoxygenic phototrophs (FAPs, also often called the green nonsulfur bacteria), and acidobacteria ( Raymond, 2008 ). In some cases (cyanobacteria and GSB), essentially all members of the phylum are phototrop2hic, while in the others, in particular the proteobacteria, the vast majority of species are not phototrophic. Small subunit rRNA evolutionary tree of life. Taxa that contain photosynthetic representatives are highlighted in color, with green highlighting indicating a type I RC, while purple highlighting indicates a type II RC. The red arrow indicates the endosymbiotic event that formed eukaryotic chloroplasts. Tree adapted from Pace (1997) . Overwhelming evidence indicates that eukaryotic photosynthesis originated from endosymbiosis of cyanobacterial-like organisms, which ultimately became chloroplasts ( Margulis, 1992 ). So the evolutionary origin of photosynthesis is to be found in the bacterial domain. Significant evidence indicates that the current distribution of photosynthesis in bacteria is the result of substantial amounts of horizontal gene transfer, which has shuffled the genetic information that codes for various parts of the photosynthetic apparatus, so that no one simple branching diagram can accurately represent the evolution of photosynthesis ( Raymond et al., 2002 ). However, there are some patterns that can be discerned from detailed analysis of the various parts of the photosynthetic apparatus, so some conclusions can be drawn. In addition, the recent explosive growth of available genomic data on all types of photosynthetic organisms promises to permit substantially more progress in unraveling this complex evolutionary process. While we often talk about the evolution of photosynthesis as if it were a concerted process, it is more useful to consider the evolution of various photosynthetic subsystems, which have clearly had distinct evolutionary trajectories. In this brief review we will discuss the evolution of photosynthetic pigments, reaction centers (RCs), light-harvesting (LH) antenna systems, electron transport pathways, and carbon fixation pathways. These subsystems clearly interact with each other, for example both the RCs and antenna systems utilize pigments, and the electron transport chains interact with both the RCs and the carbon fixation pathways. However, to a significant degree they can be considered as modules that can be analyzed individually. We know very little about the earliest origins of photosynthesis. There have been numerous suggestions as to where and how the process originated, but there is no direct evidence to support any of the possible origins ( Olson and Blankenship, 2004 ). There is suggestive evidence that photosynthetic organisms were present approximately 3.2 to 3.5 billion years ago, in the form of stromatolites, layered structures similar to forms that are produced by some modern cyanobacteria, as well as numerous microfossils that have been interpreted as arising from phototrophs ( Des Marais, 2000 ). In all these cases, phototrophs are not certain to have been the source of the fossils, but are inferred from the morphology or geological context. There is also isotopic evidence for autotrophic carbon fixation at 3.7 to 3.8 billion years ago, although there is nothing that indicates that these organisms were photosynthetic. All of these claims for early photosynthesis are highly controversial and have engendered a great deal of spirited discussion in the literature ( Buick, 2008 ). Evidence for the timing of the origin of oxygenic photosynthesis and the rise of oxygen in the atmosphere is discussed below. The accumulated evidence suggests that photosynthesis began early in Earth’s history, but was probably not one of the earliest metabolisms and that the earliest forms of photosynthesis were anoxygenic, with oxygenic forms arising significantly later. Chlorophylls are essential pigments for all phototrophic organisms. Chlorophylls are themselves the product of a long evolutionary development, and can possibly be used to help understand the evolution of other aspects of photosynthesis. Chlorophyll biosynthesis is a complex pathway with 17 or more steps ( Beale, 1999 ). The early part of the pathway is identical to heme biosynthesis in almost all steps and has clearly been recruited from that older pathway. The later steps include the insertion of magnesium and the elaboration of the ring system and its substituents. The earliest version of the pathway (and that used by most modern anoxygenic photosynthetic organisms) almost certainly was anaerobic, both not requiring and not tolerating the presence of O 2 . However, all modern oxygenic photosynthetic organisms now require O 2 as an oxidant at several steps in the pathway. This has been explained in terms of gene replacement of the genes coding for the enzymes at these steps, with the result that the overall pathway is unchanged but the enzymes at key steps are completely different in different groups of phototrophs ( Raymond and Blankenship, 2004 ). A key concept in using chlorophyll biosynthesis pathways to infer the evolution of photosynthesis is the Granick hypothesis, which states that the biosynthetic pathway of chlorophyll recapitulates the evolutionary sequence ( Granick, 1965 ). This is an appealing idea and probably at least partly true. However, in some cases, in particular the situation of chlorophyll and bacteriochlorophyll, it has been argued that the strict version of the Granick hypothesis is misleading and other interpretations are more likely ( Blankenship, 2002 ; Blankenship et al., 2007 ). All photosynthetic organisms contain carotenoids, which are essential for photoprotection, usually also function as accessory pigments, and in many cases serve as key regulatory molecules. Carotenoids, unlike chlorophylls, are also found in many other types of organisms, so their evolutionary history may reflect many other functions in addition to photosynthesis ( Sandman, 2009 ). The RC complex is at the heart of photosynthesis; so much attention has been paid to understand the evolution of RCs. A wealth of evidence, including structural, spectroscopic, thermodynamic, and molecular sequence analysis, clearly segregates all known RCs into two types of complexes, called type I and type II ( Blankenship, 2002 ). Anoxygenic phototrophs have just one type, either type I or II, while all oxygenic phototrophs have one of each type. The primary distinguishing feature of the two types of RCs are the early electron acceptor cofactors, which are FeS centers in type I RCs and pheophytin/quinone complexes in type II RCs. The distribution of RC types on the tree of life is shown in Figure 1 and a comparative electron transport diagram that compares the different RCs in different types of organisms is shown in Figure 2 , with type I RCs color coded green and type II RCs color coded purple. Electron transport diagram indicating the types or RCs and electron transport pathways found in different groups of photosynthetic organisms. The color coding is the same as for Figure 1 and highlights the electron acceptor portion of the RC. Figure courtesy of Martin Hohmann-Marriott. Further analysis strongly suggests that all RCs have evolved from a single common ancestor and have a similar protein and cofactor structure. This is clearly seen when structural overlays of both type I and II RCs are made, showing a remarkably conserved three-dimensional protein and cofactor structure, despite only minimal residual sequence identity ( Sadekar et al., 2006 ). These comparisons have been used to derive structure-based evolutionary trees that do not rely on sequence alignments. Figure 3 shows a schematic evolutionary tree of RCs that is derived from this sort of analysis. It proposes that the earliest RC was intermediate between type I and II (type 1.5) and that multiple gene duplications have given rise to the heterodimeric (two related yet distinct proteins that form the core of the RC) complexes that are found in most modern RCs. Schematic evolutionary tree showing the development of the different types of RC complexes in different types of photosynthetic organisms. This tree is based on structural comparisons of RCs by Sadekar et al. (2006) . Blue color coding indicates protein homodimer, while red indicates protein heterodimer complexes. Red stars indicate gene duplication events that led to heterodimeric RCs. Helio, Heliobacteria; GSB, green sulfur bacteria; FAP, filamentous anoxygenic phototroph. A second important issue that relates to RC evolution is the question of how both type I and II RCs came to be in cyanobacteria, while all other photosynthetic prokaryotes have only a single RC. The various proposals that have been made to explain this fact can all be divided into either fusion or selective loss scenarios or variants thereof ( Blankenship et al., 2007 ). In the fusion hypothesis, the two types of RCs develop separately in anoxygenic photosynthetic bacteria and are then brought together by a fusion of two organisms, which subsequently developed the ability to oxidize water. In the selective loss hypothesis, the two types of RCs both evolved in an ancestral organism and then loss of one or the other RC gave rise to the organisms with just one RC, while the ability to oxidize water was added later. Both scenarios have proponents, and it is not yet possible to choose between them. The primary photochemistry and several of the early secondary electron transfer reactions take place within the RC complex. However, additional electron transfer processes are necessary before the process of energy storage is complete. These include the cytochrome bc   1 and b   6 f complexes. These complexes oxidize quinols produced by photochemistry in type II RCs or via cyclic processes in type I RCs and pumps protons across the membrane that in turn contribute to the proton motive force that is used to make ATP. All phototrophic organisms have a cytochrome bc   1 or b   6 f complex of generally similar architecture, with the exception of the FAP phylum of anoxygenic phototrophs ( Yanyushin et al., 2005 ). This group contains instead a completely different type of complex that is called alternative complex III. The evolutionary origin of this complex is not yet clear. While the cytochrome bc   1 and b   6 f complexes are similar in many ways, the cytochrome c   1 and f subunits are very different and are almost certainly of distinct evolutionary origin ( Baniulis et al., 2008 ). All photosynthetic organisms contain a light-gathering antenna system, which functions to collect excitations and transfer them to the RC where the excited state energy is used to drive photochemistry ( Green and Parson, 2003 ). While the presence of an antenna is universal, the structure of the antenna complexes and even the types of pigments used in them is remarkably varied in different types of photosynthetic organisms. This very strongly suggests that the antenna complexes have been invented multiple times during the course of evolution to adapt organisms to particular photic environments. So while evolutionary relationships are clear among some categories of antennas, such as the LH1 and LH2 complexes of purple bacteria and the LHCI and LHCII complexes of eukaryotic chloroplasts, it is not possible to relate these broad categories of antennas to each other in any meaningful way. This is in contrast to the RCs, where all available evidence clearly points to a single origin that has subsequently undergone a complex evolutionary development. Most phototrophic organisms are capable of photoautotrophic metabolism, in which inorganic substrates such as water, H 2 S, CO 2 , or HCO 3   − are utilized along with light energy to produce organic carbon compounds and oxidized donor species. However, there are some groups of phototrophs that cannot carry out photoautotrophic metabolism and there are at least three entirely separate autotrophic carbon fixation pathways that are found in different types of organisms ( Thauer, 2007 ). By far the dominant carbon fixation pathway is the Calvin-Benson cycle, which is found in all oxygenic photosynthetic organisms, and also in most purple bacteria. The GSB use the reverse tricarboxylic acid cycle, and many of the FAPs use the 3-hydroxypropionate cycle ( Zarzycki et al., 2009 ). The Gram-positive heliobacteria lack any known autotrophic carbon fixation pathway and usually grow photoheterotrophically ( Asao and Madigan, 2010 ). Similarly, the aerobic anoxygenic phototrophs, which are closely related to the purple bacteria, lack any apparent ability to fix inorganic carbon. In the latter case, it seems most likely that the ancestor of this group contained the Calvin-Benson cycle but lost the genes because of their obligate aerobic lifestyle ( Swingley et al., 2007 ). The carbon fixation machinery is thus similar to the antennas, in that several entirely separate solutions have been adopted by different classes of phototrophic organisms. This would be consistent with the idea that the earliest phototrophs were photoheterotrophic, using light to assimilate organic carbon, instead of being photoautotrophic. The ability to fix inorganic carbon was then added to the metabolism somewhat later during the course of evolution, possibly borrowing carbon fixation pathways that had developed earlier in autotrophic nonphotosynthetic organisms. Perhaps the most widely discussed yet poorly understood event in the evolution of photosynthesis is the invention of the ability to use water as an electron donor, producing O 2 as a waste product and giving rise to what is now called oxygenic photosynthesis. The production of O 2 and its subsequent accumulation in the atmosphere forever changed the Earth and permitted the development of advanced life that utilized the O 2 during aerobic respiration. Several lines of geochemical evidence indicate that free O 2 began to accumulate in the atmosphere by 2.4 billion years ago, although the ability to do oxygenic photosynthesis probably began somewhat earlier ( Buick, 2008 ). In order for O 2 to accumulate, it is necessary that both the biological machinery needed to produce it has evolved, but also the reduced carbon produced must be buried by geological processes, which are controlled by geological processes such as plate tectonics and the buildup of continents. So the buildup of O 2 in the atmosphere represents a coming together of the biology that gives rise to O 2 production and the geology that permits O 2 to accumulate. Oxygen is produced by PSII in the oxygen evolving center, which contains a tetranuclear manganese complex. The evolutionary origin of the oxygen evolving center has long been a mystery. Several sources have been suggested, but so far no convincing evidence has been found to resolve this issue ( Raymond and Blankenship, 2008 ). The possibility that functional intermediate stages existed that connect the anoxygenic type II RCs to PSII seems likely ( Blankenship and Hartman, 1998 ). The process of photosynthesis originated early in Earth’s history, and has evolved to its current mechanistic diversity and phylogenetic distribution by a complex, nonlinear process. Current evidence suggests that the earliest photosynthetic organisms were anoxygenic, that all photosynthetic RCs have been derived from a single source, and that antenna systems and carbon fixation pathways have been invented multiple times. Asao M   Madigan MT ( 2010 ) Taxonomy, phylogeny, and ecology of the heliobacteria . Photosynth Res   104 : 103 – 111 Google Scholar Baniulis D   Yamashita E   Zhang H   Hasan SS   Cramer WA ( 2008 ) Structure-function of the cytochrome b   6   f complex . Photochem Photobiol   84 : 1349 – 1358 Beale S ( 1999 ) Enzymes of chlorophyll biosynthesis . Photosynth Res   60 : 43 – 73 Björn LO   Govindjee ( 2009 ) The evolution of photosynthesis and chloroplasts . Curr Sci   96 : 1466 – 1474 Blankenship RE ( 2002 ) Molecular Mechanisms of Photosynthesis . Blackwell Science, Oxford Blankenship RE   Hartman H ( 1998 ) The origin and evolution of oxygenic photosynthesis . Trends Biochem Sci   23 : 94 – 97 Blankenship RE   Sadekar S   Raymond J ( 2007 ) The evolutionary transition from anoxygenic to oxygenic photosynthesis . In   Falkowski P   Knoll AN , eds , Evolution of Aquatic Photoautotrophs . Academic Press , New York , pp 21–35 Buick R ( 2008 ) When did oxygenic photosynthesis evolve?   Philos Trans R Soc Lond B Biol Sci   363 : 2731 – 2743 Des Marais DJ ( 2000 ) Evolution: When did photosynthesis emerge on Earth?   Science   289 : 1703 – 1705 Granick S ( 1965 ) Evolution of heme and chlorophyll . In   Bryson G   Vogel HJ , eds , Evolving Genes and Proteins . Academic Press , New York , pp 67–88 Green BR   Parson WW   eds ( 2003 ) Light-Harvesting Antennas . Kluwer, Dordrecht , The Netherlands Margulis L ( 1992 ) Symbiosis in Cell Evolution . WH Freeman , San Francisco Olson JM   Blankenship RE ( 2004 ) Thinking about the evolution of photosynthesis . Photosynth Res   80 : 373 – 386 Pace NR ( 1997 ) A molecular view of microbial diversity and the biosphere . Science   276 : 734 – 740 Raymond J ( 2008 ) Coloring in the tree of life . Trends Microbiol   16 : 41 – 43 Raymond J   Blankenship RE ( 2004 ) Biosynthetic pathways, gene replacement and the antiquity of life . Geobiology   2 : 199 – 203 Raymond J   Blankenship RE ( 2008 ) The origin of the oxygen-evolving complex . Coord Chem Rev   252 : 377 – 383 Raymond J   Zhaxybayeva O   Gerdes S   Gogarten JP   Blankenship RE ( 2002 ) Whole genome analysis of photosynthetic prokaryotes . Science   298 : 1616 – 1620 Sadekar S   Raymond J   Blankenship RE ( 2006 ) Conservation of distantly related membrane proteins: photosynthetic reaction centers share a common structural core . Mol Biol Evol   23 : 2001 – 2007 Sandman G ( 2009 ) Evolution of carotenoid desaturation: the complication of a simple pathway . Arch Biochem Biophys   483 : 169 – 174 Swingley WD   Gholba S   Mastrian SD   Matthies HJ   Hao J   Ramos H   Acharya CR   Conrad AL   Taylor HL   Dejesa LC  et al.  ( 2007 ) The complete genome sequence of Roseobacter denitrificans reveals a mixotrophic rather than photosynthetic metabolism . J Bacteriol   189 : 683 – 690 Thauer RK ( 2007 ) A fifth pathway of carbon metabolism . Science   318 : 1732 – 1733 Yanyushin MF   del Rosario M   Brune DC   Blankenship RE ( 2005 ) A new class of bacterial membrane oxidoreductases . Biochemistry   44 : 10037 – 10045 Zarzycki J   Brecht V   Muller M   Fuchs G ( 2009 ) Identifying the missing steps of the autotrophic 3-hydroxypropionate CO 2 fixation cycle in Chloroflexus aurantiacus . Proc Natl Acad Sci USA   106 : 21317 – 21322 Author notes Month: Total Views: January 2021 1 February 2021 25 March 2021 67 April 2021 61 May 2021 40 June 2021 216 July 2021 210 August 2021 182 September 2021 424 October 2021 502 November 2021 390 December 2021 185 January 2022 378 February 2022 468 March 2022 429 April 2022 342 May 2022 323 June 2022 315 July 2022 204 August 2022 205 September 2022 447 October 2022 680 November 2022 415 December 2022 368 January 2023 440 February 2023 647 March 2023 443 April 2023 311 May 2023 334 June 2023 243 July 2023 222 August 2023 161 September 2023 396 October 2023 399 November 2023 390 December 2023 272 January 2024 266 February 2024 397 March 2024 392 April 2024 351 May 2024 312 June 2024 259 July 2024 164 Email alerts Citing articles via. 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It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide Copyright © 2024 Oxford University Press Cookie settings Cookie policy Privacy policy Legal notice This Feature Is Available To Subscribers Only Sign In or Create an Account This PDF is available to Subscribers Only For full access to this pdf, sign in to an existing account, or purchase an annual subscription. If you're seeing this message, it means we're having trouble loading external resources on our website. If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. AP®︎/College Biology Course: ap®︎/college biology   >   unit 3. Photosynthesis Intro to photosynthesis Breaking down photosynthesis stages Conceptual overview of light dependent reactions The light-dependent reactions The Calvin cycle Photosynthesis evolution Photosynthesis review Introduction What is photosynthesis. Energy. The glucose molecules serve as fuel for cells: their chemical energy can be harvested through processes like cellular respiration and fermentation , which generate adenosine triphosphate— ATP ‍   , a small, energy-carrying molecule—for the cell’s immediate energy needs. Fixed carbon. Carbon from carbon dioxide—inorganic carbon—can be incorporated into organic molecules; this process is called carbon fixation , and the carbon in organic molecules is also known as fixed carbon . The carbon that's fixed and incorporated into sugars during photosynthesis can be used to build other types of organic molecules needed by cells. The ecological importance of photosynthesis Photoautotrophs use light energy to convert carbon dioxide into organic compounds. This process is called photosynthesis. Chemoautotrophs extract energy from inorganic compounds by oxidizing them and use this chemical energy, rather than light energy, to convert carbon dioxide into organic compounds. This process is called chemosynthesis. Photoheterotrophs obtain energy from sunlight but must get fixed carbon in the form of organic compounds made by other organisms. Some types of prokaryotes are photoheterotrophs. Chemoheterotrophs obtain energy by oxidizing organic or inorganic compounds and, like all heterotrophs, get their fixed carbon from organic compounds made by other organisms. Animals, fungi, and many prokaryotes and protists are chemoheterotrophs. Leaves are sites of photosynthesis The light-dependent reactions and the calvin cycle. The light-dependent reactions take place in the thylakoid membrane and require a continuous supply of light energy. Chlorophylls absorb this light energy, which is converted into chemical energy through the formation of two compounds, ATP ‍   —an energy storage molecule—and NADPH ‍   —a reduced (electron-bearing) electron carrier. In this process, water molecules are also converted to oxygen gas—the oxygen we breathe! The Calvin cycle , also called the light-independent reactions , takes place in the stroma and does not directly require light. Instead, the Calvin cycle uses ATP ‍   and NADPH ‍   from the light-dependent reactions to fix carbon dioxide and produce three-carbon sugars—glyceraldehyde-3-phosphate, or G3P, molecules—which join up to form glucose. Photosynthesis vs. cellular respiration Attribution. “ Overview of Photosynthesis ” by OpenStax College, Biology, CC BY 3.0 . Download the original article for free at http://cnx.org/contents/5bb72d25-e488-4760-8da8-51bc5b86c29d@8 . “ Overview of Photosynthesis ” by OpenStax College, Concepts of Biology, CC BY 3.0 . Download the original article for free at http://cnx.org/contents/[email protected] . Works cited: "Great Oxygenation Event." Wikipedia. Last modified July 17, 2016. https://en.wikipedia.org/wiki/Great_Oxygenation_Event . Additional references Want to join the conversation. Upvote Button navigates to signup page Downvote Button navigates to signup page Flag Button navigates to signup page You are using an outdated browser. Please upgrade your browser or activate Google Chrome Frame to improve your experience. Account Home Activities and Experiments to Explore Photosynthesis in the Classroom Photosynthesis can be a difficult concept to grasp, that’s why we’ve compiled a selection of hands-on activities and experiments to help show students some of the concepts in action. In addition to the ideas below, PLT’s new Explore Your Environment: K-8 Activity Guide and PLT’s PreK-8 Environmental Education Activity Guide both offer a wealth of hands-on, creative activities and resources for lessons about photosynthesis. Each guide includes a comprehensive Topic Index to help you quickly find a list of relevant activities that fit your needs and every activity includes a background section for educators that gives a science-based introduction to the activity’s content. We also have a few abridged versions related to the physiology of trees and photosynthesis for families to try out together at home, for example, How Plants Grow and Tree Factory . Introduction to Photosynthesis The word “photosynthesis” comes from Greek root words that combine to mean “to put together with the help of light.” All plants, algae, and some microorganisms like bacteria photosynthesize to make their own food. This makes them part of a group of organisms called autotrophs. Unlike heterotrophs, which include animals that feed off other living organisms, autotrophs make nutritional organic substances from simple inorganic substances. What a superpower! To undergo photosynthesis, plants need carbon dioxide from the air, water from the soil, and sunlight. These elements combine in a chemical reaction that takes place inside of a plant’s leaves to create glucose and oxygen. Absorbing Carbon Dioxide and Water Carbon dioxide can be produced naturally from the decomposition of living things and events like volcanic eruptions, and from human activity like burning fossil fuels. Animals respirate by inhaling gases in the air, retaining oxygen, and releasing carbon dioxide. However, when plants breathe, they take in carbon dioxide, which is a key ingredient required for photosynthesis. Carbon dioxide enters a plant through its stomata, tiny pores that are usually located on the underside of leaves and sometimes stems. Most plants also soak up another substance through their roots that they need for photosynthesis: water. Adding Energy Once a plant has carbon dioxide and water, it needs energy to enable these two substances to chemically react with each other. It gets energy from a steady stream of sunlight hitting its leaves. Chlorophyll, a green pigment found in tiny structures called chloroplasts within leaves, absorbs energy from blue and red light waves from the sun. The sunlight’s energy is then transferred to two types of energy-storing molecules within the plant. The energy already stored from the sun fuels a reaction in the leaves’ chloroplasts that splits water molecules (H 2 0) into pure hydrogen (H) and oxygen (O 2 ). The hydrogen reacts with carbon dioxide (CO 2 ) to produce glucose, a type of sugar. The full chemical equation of photosynthesis looks like this: 6CO 2 + 6H 2 0 + Sunlight → C 6 H 12 O 6 + 6O 2 In other words, the carbon dioxide and water that go into the plant combine with energy from sunlight to produce glucose, and also oxygen. Storing and Using Glucose Once this sugar is made, it can be stored as energy (food) that the plant uses for growth and repair. Plants also use the energy from nutrients in the soil along with glucose to grow and develop leaves, flowers, and fruits. Students often wonder how a gas like carbon dioxide that you can’t see helps form a giant tree or the apple they eat for lunch. It’s because a chemical reaction doesn’t have to start with a solid (like soil) to end with a solid (like a tree or apple). It helps for students to understand the carbon cycle – and PLT has a variety of content to support this. Glucose is a carbohydrate, which is simply a molecule containing carbon, hydrogen, and oxygen. Smaller glucose molecules can build bigger carbohydrates like cellulose or starch. Similar to a human skeleton, cellulose is the main component of plant cell walls that help strengthen the plant. Humans can’t digest cellulose, but the fiber found in cellulose-heavy foods like celery and broccoli aids with digestion and can lower the risk of diseases like cancer. These strong fibers are also used to make clothes and paper. Animals like cows, horses, and sheep can digest cellulose, so it makes sense that they eat grass for quick energy and nutrients. Plants can also convert glucose into starch, which is a larger carbohydrate molecule that can store its energy. Humans break down starches found in foods like potatoes and rice into glucose, and it, in turn, gives them energy. Though you may not use sunlight to create your food, when you eat something like chicken or rice, you take in energy plants used from the sun. And not only does a plant produce food animals need for their energy as a result of photosynthesis, but it also releases oxygen as a byproduct through its stomata into the atmosphere. Photosynthesis is critical for the survival of all living organisms — not just plants. Hands-On Photosynthesis Activities Photosynthesis can be a difficult concept to grasp, especially for younger learners. That’s why we’ve compiled these interactive activities and experiments that show some of the concepts in action. Photosynthesis Visuals These photosynthesis modeling activities will help students visualize and better understand what a plant needs to undergo photosynthesis and what it produces as a result. The 3D and 2D representations will also help them absorb some of the vocabulary associated with photosynthesis. 3D Photosynthesis: Tree Leaf Model  Older students can create these more complex 3D models of a leaf’s front and backside where all of the photosynthesis action takes place, like on its stomata and chloroplasts. They will attach labels to the leaf that describe the different substances involved. The Ins and Outs of Photosynthesis Younger learners will enjoy this less complex visual activity that involves a leaf with “IN” and “OUT” envelopes into which they’ll place the respective chemical reactants or products of photosynthesis. Photosynthesis Paper Craft   Take your lesson in an artistic direction by letting students create these bright and fun paper flower and sun displays, complete with the basic photosynthesis terms. Exploring Leaves with STEM  These STEM experiments requiring real leaves will spark valuable critical thinking when students observe leaf structure, stomata, plant respiration, and more. Respirating Leaves The invisible chemical process of a leaf exchanging carbon dioxide, water, and sunlight for oxygen will become visible when your class observes what happens when they submerge leaves in water. Stomata Microscope Investigation Students will use microscopes to explore the structure of a leaf that makes the exchange of gasses during photosynthesis possible. They can also explore other parts of leaves and how plants gain mass. Stomata Microscope Comparison Compare the stomata sizes and numbers of different plant species under a microscope and examine leaf texture by creating cool “nail polish imprints.” Exploring Plants and Sunlight Plants need sunlight for survival, so it makes sense that their behavior or appearance would change if their access to sunlight is altered. These activities explore this concept. Measuring Plant Growth with Sunlight  This activity takes a couple of weeks but will give your students valuable insight into how a plant’s growth and green coloration is affected by varying levels of sunlight over time. They’ll flex their critical thinking skills as they take daily notes and conclude what happens to a seed under different light conditions. Rotating Plants Track how plants bend towards the sun wherever they are with this great exercise that introduces young students to just how active plants can be when it comes to gaining precious sun energy. You can grow seedlings or even experiment with a larger plant you have and see how its color or growth is affected when you rotate or move closer or further from the sun. Fun with Plant Pigmentation  There’s a lot of fun that can be had with the chlorophyll in leaves, including art and color experimentation!  Chlorophyll Paintings  Chlorophyll pigment not only turns plants green – it makes leaves great mediums for “green” art projects! Kids will love this out-of-the-box painting style, learn about chlorophyll firsthand, and expand their creativity all at once. Leaf Color Chemistry Experiment  When the school year begins, recreate how leaves change color in autumn with green leaves, rubbing alcohol, coffee filters, and other easy-to-find items. The pigments of chlorophyll will fade and leave behind hidden pigments that demonstrate why leaves change color in the fall – which is also when your class can reflect back on this eye-opening experiment. Let Project Learning Tree Be Your Guide Introduce students to photosynthesis with these PLT activities from the new Explore Your Environment: K-8 Activity Guide : Here We Grow Again (for grades K-2), Every Tree for Itself , and Signs of Fall (for grades 3-5) in PLT’s Explore Your Environment: K-8 Activity Guide How Plants Grow and Sunlight and Shades of Green (Activities 41 and 42 in PLT’s PreK-8 Environmental Education Activity Guide ), and Power Plants (Activity 4 in PLT’s Energy & Ecosystems E-Unit). Watch an example of an activity! This video walks viewers through PLT’s activity Signs of Fall. In this activity, participants are introduced to different leaf pigments and use chromatography to pull out leaf pigments using simple household items. It helps answer the question, “Why do leaves change color?”. For further guidance on how to relay the essential concepts of photosynthesis to your classroom and more great activities, check out this Unit of Instruction by Project Learning Tree. It suggests linking select PLT activities to help students learn more about the topic of photosynthesis using a storyline technique. Storylines ensure connectivity and continuity between individual activities and can serve as the “instructional glue” that bind many areas of knowledge and skills. The Unit of Instruction includes a guiding question, concepts addressed, and connections to the Next Generation Science Standards (NGSS) and PLT’s Forest Literacy Framework. To boost your teaching with 50 field-tested, hands-on multidisciplinary activities that educate and connect elementary students with nature in powerful ways, and more suggested Units of Instruction , look no further than Project Learning Tree’s new Explore Your Environment: K-8 Activity Guide . Rebecca Reynandez Leave a reply cancel reply. Your email address will not be published. Required fields are marked * You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong> Save my name, email, and website in this browser for the next time I comment. This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Earth Day 2021 Celebrate Earth Day with some inspiring stories and resources to help youth learn about sustainability issues, climate science, and the actions they can take. Environmental Education Resources Every month we carefully select new educational apps, videos, interactive websites, books, careers information, and teacher-generated materials that support PLT lessons. STEM: Poet-Tree Engage students in STEM (science, technology, engineering, and math) through the power of the written word. Try these enrichments for Project Learning Tree’s Poet-Tree activity. PreK-8 Environmental Education Activity Guide – Activity 51, Make Your Own Paper Students investigate the papermaking process by trying it themselves. Students are thrilled to find that they can make paper and that their product is practical, as well as beautiful. Watch a video of the paper-making process used in this activity. MAKE LEARNING FUN ATTEND A TRAINING Get our educational materials and professional development by participating in an in-person workshop or an online course. CONTACT YOUR COORDINATOR Get information relevant to your state, plus local assistance and connections to resources and professionals in your community. EDUCATOR TIPS Get a wealth of up-to-date resources, support, and ideas from teachers and other educators. 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If so, what sort of implications might this hold for the prospect of growing food in outer space? PNNL scientists are exploring these questions and more. (Photo by Andrea Starr | Pacific Northwest National Laboratory) CAPE CANAVERAL, Fla.—An experiment aimed at learning more about how plants grow in space will be aboard a National Aeronautics and Space Administration  launch in early August from the Cape Canaveral Space Force Station in Florida. A Northrop Grumman Cygnus spacecraft perched atop a SpaceX Falcon 9 rocket will carry the plants to the orbiting laboratory, where astronauts will tend to them before the plants are returned to Earth. ( Update: The launch occurred at 8:02 a.m. Pacific Time Sunday, August 4.) The experiment created by scientists at the Department of Energy’s Pacific Northwest National Laboratory will look at how two different types of grass grow on the space station. A PNNL team led by biologist Pubudu Handakumbura designed the experiment and will compare the results from space to identical plants being grown at the Kennedy Space Center. The study focuses on photosynthesis—how the plants take in light and then use it to grow, converting carbon dioxide to sugars and oxygen in the process. The two grass types under study, Brachypodium distachyon and Setaria viridis , use different carbon dioxide-concentrating mechanisms. Handakumbura’s team will compare the two methods in a microgravity environment. While most plants on Earth use a carbon-concentrating mechanism known as C3, there is some evidence that a method known as C4 holds more promise for plant growth in space. “How will the plants respond in a microgravity environment?” said Handakumbura. “Plants naturally send their roots downward due to gravity. But how will they grow in microgravity? This is important for future deep space exploration, for growing food and supporting life.” The team will monitor three identical sets of plants as they grow for 32 days—two sets at Kennedy Space Center and one set on the space station. Altogether, the experiment includes 288 plants. On the space station, astronauts will tend to the plants and record how efficiently they are carrying out photosynthesis. After the plants are returned to Earth on a subsequent mission, they will be sent to PNNL, where Handakumbura’s team will spend several months analyzing the molecular activity that took place. The experiments measuring proteins, metabolites and other molecules will be done at the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility. Handakumbura’s experiment, funded by NASA, is named Advanced Plant Experiment-09 or APEX-09 . PNNL colleagues Chaevien Clendinen, Summer Duckworth, Kim Hixson, Madeline Southworth and Kylee Tate are also working on the project. Handakumbura will be on hand to watch the experiment, three years in the making, head into space as part of Northrop Grumman’s 21 st Commercial Resupply Services Mission. “I look forward to the knowledge we will uncover from the team-driven science we are conducting with APEX 09,” said Handakumbura. “And I am excited to contribute to the foundational research that will shape future plant system designs.” Pacific Northwest National Laboratory draws on its distinguishing strengths in chemistry , Earth sciences , biology and data science to advance scientific knowledge and address challenges in sustainable energy and national security . Founded in 1965, PNNL is operated by Battelle for the Department of Energy’s Office of Science, which is the single largest supporter of basic research in the physical sciences in the United States. DOE’s Office of Science is working to address some of the most pressing challenges of our time. For more information, visit https://www.energy.gov/science/ . For more information on PNNL, visit PNNL's News Center . Follow us on Twitter , Facebook , LinkedIn and Instagram . Published: August 1, 2024 Research topics share this! August 2, 2024 This article has been reviewed according to Science X's editorial process and policies . Editors have highlighted the following attributes while ensuring the content's credibility: fact-checked trusted source Experiment on photosynthesis is heading to the space station to explore effects of microgravity by Tom Rickey, Pacific Northwest National Laboratory An experiment aimed at learning more about how plants grow in space will be aboard a National Aeronautics and Space Administration launch in early August from the Cape Canaveral Space Force Station in Florida. A Northrop Grumman Cygnus spacecraft perched atop a SpaceX Falcon 9 rocket will carry the plants to the orbiting laboratory, where astronauts will tend to them before the plants are returned to Earth. The experiment created by scientists at the Department of Energy's Pacific Northwest National Laboratory will look at how two different types of grass grow on the space station. A PNNL team led by biologist Pubudu Handakumbura designed the experiment and will compare the results from space to identical plants being grown at the Kennedy Space Center. The study focuses on photosynthesis—how plants take in light and then use it to grow, converting carbon dioxide to sugars and oxygen in the process. The two grass types under study, Brachypodium distachyon and Setaria viridis, use different carbon dioxide -concentrating mechanisms. Handakumbura's team will compare the two methods in a microgravity environment. While most plants on Earth use a carbon-concentrating mechanism known as C3, there is some evidence that a method known as C4 holds more promise for plant growth in space. "How will the plants respond in a microgravity environment?" said Handakumbura. "Plants naturally send their roots downward due to gravity. But how will they grow in microgravity? This is important for future deep space exploration, for growing food and supporting life." The team will monitor three identical sets of plants as they grow for 32 days—two sets at Kennedy Space Center and one set on the space station. Altogether, the experiment includes 288 plants. On the space station , astronauts will tend to the plants and record how efficiently they are carrying out photosynthesis. After the plants are returned to Earth on a subsequent mission, they will be sent to PNNL, where Handakumbura's team will spend several months analyzing the molecular activity that took place. The experiments measuring proteins, metabolites and other molecules will be done at the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility. Handakumbura's experiment is named Advanced Plant Experiment-09 or APEX-09 . PNNL colleagues Chaevien Clendinen, Summer Duckworth, Kim Hixson, Madeline Southworth and Kylee Tate are also working on the project. Handakumbura will be on hand to watch the experiment, three years in the making, head into space as part of Northrop Grumman's 21st Commercial Resupply Services Mission. "I look forward to the knowledge we will uncover from the team-driven science we are conducting with APEX 09," said Handakumbura. "And I am excited to contribute to the foundational research that will shape future plant system designs." 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More about Ben Hubbard Advertisement 321 COMMENTS The Discovery of Photosynthesis- Early Experiments Photosynthesis Discovery - Early Experiments. Since photosynthesis is a light-dependant process, it only takes place in the presence of sunlight. But along with sunlight, the plant also requires water and carbon dioxide as raw materials for this process to synthesise carbohydrates. Green plants also possess a green pigment known as ... 3.1: Discovery of Photosynthesis The history of the studies done on photosynthesis dates back into the 17th century with Jan Baptist van Helmont. He rejected the ancient idea that plants take most of their biomass from the soil. For the proof, he performed willow tree experiment. He started with a willow tree of 2.27 kg. Over 5 years, it grew to 67.7 kg. Photosynthesis: basics, history and modelling Joseph Priestley (1776) showed, in elegant experiments, that plants produced 'oxygen' (then called de-phlogisticated air) needed by a mouse to live, whereas Jan Ingen-Housz (1773) convincingly established that light was necessary for photosynthesis. ... Mechanistic models for early events in photosynthesis. Bay and Pearlstein (1963) ... Photosynthesis: basics, history and modelling Joseph Priestley (1776) showed, in elegant experiments, that plants produced 'oxygen' (then called de-phlogisticated air) needed by a mouse to live, whereas Jan Ingen-Housz (1773) convincingly established that light was necessary for photosynthesis. ... Mechanistic models for early events in photosynthesis. Bay and Pearlstein (1963) ... History and Early Development of Photosynthesis The equation of photosynthesis. Early mechanistic ideas of photosynthesis. The Emerson and Arnold experiments. The controversy over the quantum requirement of photosynthesis. The red drop and the Emerson enhancement effect. Antagonistic effects. Early formulations of the Z scheme for photosynthesis. ATP formation and carbon fixation Photosynthesis Photosynthesis usually refers to oxygenic photosynthesis, ... The first photosynthetic organisms probably evolved early in the evolutionary history of life using reducing agents such as hydrogen or hydrogen sulfide, ... These two experiments illustrate several important points: First, it is known that, ... Early Pioneers of Photosynthesis Research His early experiments were measurements of the quantities of moisture taken in by the roots and transpired by the leaves. Using rudimentary laboratory apparatus and hydrostatic principles, he made many attempts to calculate the force with which the sap moves. ... The early workers in photosynthesis, from Van Helmont through de Saussure, were ... 8.2: Photosynthesis This page titled 8.2: Photosynthesis - Dicovering the Secrets is shared under a CC BY 3.0 license and was authored, remixed, and/or curated by John W. Kimball via source content that was edited to the style and standards of the LibreTexts platform. This chapter talks about various scientists and their path towards discovering photosynthesis. Early Evolution of Photosynthesis The process of photosynthesis originated early in Earth's history, and has evolved to its current mechanistic diversity and phylogenetic distribution by a complex, nonlinear process. Current evidence suggests that the earliest photosynthetic organisms were anoxygenic, that all photosynthetic RCs have been derived from a single source, and ... Early experiments of photosynthesis In this article, we will take a closer look at the early photosynthesis experiments. Process of photosynthesis. Photosynthesis is how green plants and some kinds of microorganisms use sunlight to synthesise nutrients from carbon dioxide and water. It is a chemical reaction that converts light energy into chemical energy (through the absorption ... Photosynthesis Photosynthesis is 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. ... (18 O) was used in early experiments. Plants that ... Early Experiments to Understand Photosynthesis: Meaning, History Summary. Photosynthesis is the process used by green plants to form glucose molecules by using water, carbon dioxide and chlorophyll molecules. Various scientists performed several experiments to prove the usage of light and carbon dioxide in the formation of food in plants. Scientists like Priestley and Ingenhousz proved that the plants in the ... Early Experiments on Photosynthesis Photosynthesis Discovery - Early Experiments. The process of photosynthesis is carried by some of the required raw materials like water, carbon dioxide, and cellular components like plastids. Plants make use of these raw materials to synthesize carbohydrates in the presence of sunlight. These key features of photosynthesis were revealed ... Photosynthesis I Photosynthesis is a process by which an organism converts light energy from the sun into chemical energy for its sustenance. Photosynthesis occurs in plants, algae, and some species of bacteria. ... Early experiments towards the discovery of photosynthesis. Priestley, partially credited with the discovery of elemental oxygen, found that when he ... Photosynthesis In the first half of the seventeenth century, Jan Baptista van Helmont (1579-1644), a Dutch physician, chemist, and alchemist, performed important experiments which disproved this early view of photosynthesis. He grew a willow tree weighing 5 lb (2.5 kg) in a clay pot which had 200 lb (91 kg) of soil. Five years later, after watering his willow ... The Discovery of Photosynthesis At09kg - CC 3.0. Photosynthesis is a very important and complex process in nature and some of its phases are still not completely understood. Photosynthesis in plants and a few bacteria is responsible for feeding nearly all life on Earth. It does this by taking energy from the sun and converting it into a storable form, usually glucose, which ... Early Experiments on Photosynthesis The early experiments conducted to prove photosynthesis involved proving the essentiality of carbon dioxide and sunlight in the process. These experiments were conducted by various scientists including Joseph Priestley, Jan Ingenhousz, Jean Senebier, Julius Robert Mayer, Julius Von Sachs, T.W.Engelmann, and Cornelius van Niel. Early Evolution of Photosynthesis A wealth of evidence indicates that photosynthesis is an ancient process that originated not long after the origin of life and has evolved via a complex path to produce the distribution of types of photosynthetic organisms and metabolisms that are found today ( Blankenship, 2002; Björn and Govindjee, 2009 ). Figure 1 shows an evolutionary tree ... Intro to photosynthesis (article) Photosynthesis is the process in which light energy is converted to chemical energy in the form of sugars. In a process driven by light energy, glucose molecules (or other sugars) are constructed from water and carbon dioxide, and oxygen is released as a byproduct. The glucose molecules provide organisms with two crucial resources: energy and ... Early Experiments of Photosynthesis Early Experiments of Photosynthesis . Biology . definition. Introduction to the history of photosynthesis There are the scientists who explained the life-sustaining process, photosynthesis. Aristotle: Over two thousand years ago, he said that plant absorbs all the inorganic and organic material directly from the soil. Photosynthesis early experiments Photosynthesis early experiments This page discusses some of the experiments that were carried out by early scientists in order to gain a better understanding of photosynthesis. Share. Introduction. Photosynthesis is the process through which plants make the food they need to survive. In this process, light energy is absorbed by the plants and ... Activities and Experiments to Explore Photosynthesis in the Classroom The energy already stored from the sun fuels a reaction in the leaves' chloroplasts that splits water molecules (H 2 0) into pure hydrogen (H) and oxygen (O 2 ). The hydrogen reacts with carbon dioxide (CO 2) to produce glucose, a type of sugar. The full chemical equation of photosynthesis looks like this: 6CO2 + 6H20 + Sunlight → C6H12O6 ... Experiment on Photosynthesis by Scientists at PNNL Headed to the Space CAPE CANAVERAL, Fla.—An experiment aimed at learning more about how plants grow in space will be aboard a National Aeronautics and Space Administration launch in early August from the Cape Canaveral Space Force Station in Florida.. A Northrop Grumman Cygnus spacecraft perched atop a SpaceX Falcon 9 rocket will carry the plants to the orbiting laboratory, where astronauts will tend to them ... Experiment on photosynthesis is heading to the space station to explore An experiment aimed at learning more about how plants grow in space will be aboard a National Aeronautics and Space Administration launch in early August from the Cape Canaveral Space Force ... Scientists untangle interactions between the Earth's early life forms Scientists untangle interactions between the Earth's early life forms and the environment over 500 million years. ScienceDaily . Retrieved August 2, 2024 from www.sciencedaily.com / releases ... An Escalating War in the Middle East Tensions are on a knife edge after Israel carried out a strike on the Hezbollah leader allegedly behind an attack in the Golan Heights. essay homework paper phd review speech study thesis