The History of Photosynthesis Research: Key Discoveries and Scientists

The history of photosynthesis research began in 1761, when the Russian scientist Mikhail Lomonosov first proposed the idea that plants feed on air, though he had no experimental evidence to support it. Over the next two and a half centuries, a chain of discoveries — from sealed-jar experiments to molecular phylogenetics — revealed photosynthesis as the process that sustains nearly all life on Earth. Photosynthesis in plants

What is photosynthesis: definition and overview

Photosynthesis is the process by which green plants, algae, and certain bacteria convert light energy into chemical energy, using carbon dioxide and water to build carbohydrates and releasing oxygen as a by-product. In its most common, oxygen-producing form, photosynthesis can be summarised by a single chemical equation:

6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂

Photosynthesis matters because it is the primary entry point of energy into the biosphere. It produces the oxygen that aerobic organisms breathe, removes carbon dioxide from the atmosphere, and builds the plant biomass — sugars, cellulose, starch — on which food chains, fossil fuels, fibre materials, and biofuels ultimately depend. The carbohydrates formed in plants supply the carbon skeletons and stored energy for virtually all other living things.

Organisms that carry out photosynthesis fall into two broad groups. Photoautotrophs, such as plants and cyanobacteria, use light energy to fix carbon dioxide into organic matter. Photoheterotrophs, found among some bacteria, capture light for energy but obtain their carbon from organic compounds rather than from carbon dioxide. This distinction becomes important when tracing how photosynthesis first evolved.

Early ideas on the air-feeding of plants: Mikhail Lomonosov

Mikhail Lomonosov advanced the first recorded idea of air-feeding in plants in 1761, suggesting that plants draw nourishment from the air rather than solely from the soil. This was a remarkable conceptual leap for its time, but Lomonosov offered no experiments to test it, and the notion remained speculative until later researchers could demonstrate the gas exchange involved.

How plants affect the composition of air: Joseph Priestley's experiments

Joseph Priestley first studied the influence of plants on the surrounding air in 1773, using sealed glass jars to compare living things under controlled conditions. In his experiments a mouse placed under a glass bell jar died, but a mouse kept under the same bell jar together with a sprig of mint stayed alive. From this Priestley concluded that plants can "restore" or purify air that animals had spoiled. Priestley's experiment

Priestley's first experiments missed a crucial point: that this restoration of the air happens only in the light. Working independently and then together with Joseph Priestley, Jan Ingenhousz showed in 1779 that plants can restore air only in the light, while in darkness they spoil the air just as animals do, consuming oxygen and releasing carbon dioxide.

The restoration of air in the light is a property only of the green parts of the plant. These experiments thus produced the first evidence that plants carry out two directly opposing processes affecting the composition of air — what we now call photosynthesis and respiration. Neither Priestley nor Ingenhousz, however, grasped what this "restoration" of air actually meant for the plant itself.

The discovery of oxygen as a distinct gas

The gas that plants release in the light was identified as oxygen — a distinct chemical element — through the work of Joseph Priestley, who isolated it in 1774, and Antoine-Laurent Lavoisier, who named it and explained its role in combustion and respiration. Lavoisier's recognition that respiration consumes oxygen and that burning is oxidation gave the plant experiments their chemical meaning: plants were not merely "purifying" air, they were producing the very gas that animals and flames consume.

The role of light: Jan Ingenhousz's research

Jan Ingenhousz established that light is essential to the air-restoring activity of plants, demonstrating that the green parts of plants release oxygen only when illuminated and absorb it in the dark. His 1779 findings turned a vague observation into a clear rule and laid the groundwork for understanding light as the driving condition of photosynthesis, even though the energetic role of light would not be explained for another century.

The process of carbon nutrition: Jean Senebier's work

Jean Senebier proved in 1782 that the uptake of carbon dioxide and the release of oxygen in the light constitute a process of carbon nutrition, in which carbon accumulates in the plant body. Senebier was the first to give a correct explanation of the essence of plant gas exchange, linking the disappearance of carbon dioxide directly to the building of plant material.

The quantitative experiments of Nicolas de Saussure

The series of discoveries in photosynthesis culminated in the experiments of Nicolas de Saussure in 1804, who showed quantitatively that the volumes of oxygen and carbon dioxide exchanged in the process are equal, and that water is consumed alongside carbon dioxide. He inferred this because the gain in the plant's dry mass significantly exceeded the weight of carbon supplied by the carbon dioxide. In this way the origin of carbon, oxygen, and hydrogen in plants was established. Gas exchange in plants

Through the eighteenth and early nineteenth centuries, then, the basic principles of plant air-feeding were worked out: the absorption of carbon dioxide, the release of oxygen, the necessity of light and chlorophyll, and the nature of the end products. Yet exactly what role light played remained unclear.

Synthesis of carbon compounds from carbonic acid

The synthesis of organic carbon compounds from carbonic acid (carbon dioxide dissolved in water) is the chemical heart of photosynthesis. Building on Senebier and Saussure, nineteenth-century researchers established that the carbon entering the plant is reduced and assembled into carbohydrates such as glucose, which are then converted into starch, cellulose, and other plant biomass. This synthesis is what makes plants the principal producers of organic matter on Earth, supplying the raw material for food, fibre, and fuel.

The energetic side of photosynthesis: Kliment Timiryazev

Kliment Timiryazev advanced the understanding of photosynthesis to a new stage by studying its energetic side and the role of light. He showed that the light absorbed by chlorophyll is required as a source of energy, and he demonstrated that the law of conservation of energy applies to the process of photosynthesis.

The law of conservation of energy and the conversion of light energy

Timiryazev's central insight was that photosynthesis is fundamentally an energy conversion: the radiant energy of sunlight is captured by chlorophyll and stored as chemical energy in the bonds of carbohydrate molecules. By applying the law of conservation of energy, he established that plants do not create energy but transform solar energy into a chemical form. He also showed that the red and blue regions of the spectrum, which chlorophyll absorbs most strongly, are the most effective in driving photosynthesis — a direct link between the light spectrum and the photosynthetic pigments.

The study of pigments: Willstätter and Mikhail Tsvet

Major contributions to the study of the pigments involved in photosynthesis came from Richard Willstätter, who determined the chemical formula of chlorophyll and the carotenoids, and from Mikhail Tsvet, who developed the chromatographic method for separating leaf pigments. Tsvet's chromatography became a foundational analytical technique far beyond plant science, allowing researchers to resolve the mixture of chlorophylls and accessory pigments present in a leaf.

Chlorophyll and the absorption of light

Chlorophyll is the green pigment that absorbs light to power photosynthesis, capturing energy most efficiently in the blue and red parts of the visible spectrum while reflecting green, which is why plants appear green. A classic demonstration of which wavelengths drive photosynthesis came from Theodor Engelmann, who used the filamentous green alga Spirogyra and oxygen-seeking bacteria as a living light meter: the bacteria clustered along the alga where it released the most oxygen, in the red and blue bands of a spectrum projected onto the cell. This elegant experiment in bacterial photometry confirmed that chlorophyll's absorption peaks coincide with the wavelengths most effective for photosynthesis.

Blackman's experiments: light and temperature in photosynthesis

Frederick Blackman demonstrated in the early 1900s that photosynthesis consists of two distinct kinds of reactions — one dependent on light, the other not. By varying light intensity and temperature separately, Blackman showed that at low light the rate of photosynthesis depended on light and was unaffected by temperature, while at high light it became temperature-dependent. From this he concluded that photosynthesis involves a fast, light-driven photochemical stage followed by slower, temperature-sensitive enzymatic ("dark") reactions. This two-stage model framed the modern division of photosynthesis into light-dependent and light-independent reactions.

The light-dependent reactions take place in the thylakoid membranes and capture light energy, using it to split water, release oxygen, and generate the energy carriers ATP and NADPH. The light-independent reactions then use that ATP and NADPH to fix carbon dioxide into sugars, and they proceed through enzymes without directly requiring light. Blackman's separation of the two phases was the conceptual bridge between the classical gas-exchange studies and the biochemistry of the twentieth century.

The appearance of the term "photosynthesis": Charles Barnes

The word "photosynthesis" was proposed in 1893 by the American botanist Charles Barnes, who suggested a Greek-derived term for the process of carbon assimilation in the light. Barnes actually put forward two candidate terms — "photosyntax" and "photosynthesis" — and initially favoured "photosyntax," but it was "photosynthesis" that the scientific community adopted and that the Oxford English Dictionary later recorded as the standard usage.

The evolution of photosynthetic terminology

The debate between "photosyntax" and "photosynthesis" illustrates how scientific terminology evolves through usage rather than decree. Barnes preferred "photosyntax" to emphasise the orderly arrangement of carbon, but other botanists found "photosynthesis" — literally "putting together with light" — more intuitive, and that term prevailed. The semantic shift continued through the twentieth century: as the discovery of photophosphorylation showed that light could also generate ATP without immediate carbon fixation, scientists periodically reconsidered exactly what the definition of photosynthesis should encompass, gradually broadening it from "carbon assimilation in light" to the wider conversion of light energy into chemical energy.

The ecology of photosynthesis: contributions of Russian scientists

The ecology of photosynthesis was studied by many Russian scientists, including S. P. Kostychev, V. N. Lyubimenko, A. A. Ivanov, Dmitri Ivanovsky, and A. A. Richter, who examined how photosynthesis responds to environmental conditions. Their work connected the laboratory chemistry of the process to the behaviour of whole plants in natural settings, an essential step toward understanding photosynthetic efficiency in crops and ecosystems.

The development of photosynthesis chemistry in the twentieth century

The chemistry of photosynthesis was studied intensively in the twentieth century, including in the 1970s by A. N. Terenin, A. A. Krasnovsky, A. A. Nichiporovich, and T. N. Godnev, and abroad by Otto Warburg, Melvin Calvin, Eugene Rabinowitch, and others. This era moved the field from describing gas exchange to mapping the actual molecular pathways by which carbon dioxide becomes sugar.

The Calvin cycle and the synthesis of carbohydrates

The Calvin cycle is the set of light-independent enzymatic reactions that fix carbon dioxide into carbohydrates, named after Melvin Calvin, who mapped it using radioactive carbon-14 traced through the pathway. In the cycle, carbon dioxide combines with the five-carbon sugar ribulose bisphosphate, and the resulting compounds are reduced using the ATP and NADPH made in the light reactions to produce glucose and regenerate the starting molecule. In many plants this is the only route of carbon fixation, while others use a C4 pathway that concentrates carbon dioxide before it enters the Calvin cycle, improving photosynthetic efficiency in hot, bright climates. A related complication is photorespiration, a competing reaction in which the same enzyme binds oxygen instead of carbon dioxide and wastes fixed carbon; reducing photorespiration is a major target in efforts to optimise crop yields.

Chloroplast structure and its ultrastructure

The chloroplast is the organelle inside plant and algal cells where photosynthesis takes place, and its internal architecture reflects the two stages of the process. Its ultrastructure includes a double outer membrane, a fluid interior called the stroma where the Calvin cycle operates, and an internal system of flattened membrane sacs called thylakoids, stacked into grana, which house the chlorophyll and the machinery of the light-dependent reactions. Leaf structure complements this: leaves are flattened to maximise light capture, packed with chloroplast-rich cells, and equipped with pores (stomata) that admit carbon dioxide — adaptations that together make the leaf an efficient photosynthetic organ.

The discovery of bacterial photosynthesis

Bacterial photosynthesis was recognised in the early twentieth century when researchers found that certain bacteria capture light energy without producing oxygen. This discovery reshaped the definition of photosynthesis, showing that the oxygen-releasing version found in plants is only one variant of a much older and more diverse process. Cornelis van Niel made a key contribution by proposing a general equation for photosynthesis in which water in plants and other compounds such as hydrogen sulfide in bacteria play the same hydrogen-donor role — a unifying insight that explained why some photosynthetic organisms release oxygen and others do not.

Anoxygenic photosynthetic bacteria

Anoxygenic photosynthetic bacteria are organisms that perform photosynthesis without releasing oxygen, using molecules other than water as their source of electrons. This group includes the purple bacteria, the green bacteria, and the heliobacteria, which capture light with bacteriochlorophyll and often live in environments such as sulfur-rich sediments or deep water layers. Because they split compounds like hydrogen sulfide rather than water, they produce sulfur or other by-products instead of oxygen, distinguishing them sharply from oxygenic organisms such as plants and cyanobacteria.

Ancient photosystems in bacteria

The photosystems — the light-capturing protein-pigment complexes — found in modern bacteria are among the most ancient biological structures, predating the oxygen-producing apparatus of plants. Researchers including Jin Xiong and Carl E. Bauer at Indiana University analysed the genes encoding these reaction centres and concluded that the basic photosynthetic machinery arose in bacteria long before oxygenic photosynthesis appeared. Their molecular work, published in the journal Science, used gene-sequence comparisons to reconstruct the deep history of these complexes and is also reflected in the literature of journals such as Photosynthesis Research.

Variants of bacterial photosynthesis

Bacterial photosynthesis comes in several distinct variants that differ in their pigments, electron donors, and reaction centres:

• Purple bacteria use a single type of reaction centre and bacteriochlorophyll, drawing electrons from compounds such as hydrogen sulfide or organic molecules, and do not produce oxygen.
• Green bacteria capture light with specialised antenna structures and likewise carry out anoxygenic photosynthesis.
• Heliobacteria use a unique bacteriochlorophyll and occupy a distinctive position in the evolutionary tree of photosynthetic organisms.
• Cyanobacteria are the exception: they evolved two linked photosystems that split water and release oxygen, making them the only bacteria to carry out oxygenic photosynthesis.

A separate, light-driven strategy is found in organisms such as Halobacterium, which uses the pigment-protein bacteriorhodopsin to pump ions and harvest light energy without chlorophyll or carbon fixation — a reminder that nature has evolved more than one way to live on sunlight.

The evolution of photosynthesis: from cyanobacteria to chloroplasts

The chloroplasts of plants and algae descend from free-living cyanobacteria that were engulfed by an early host cell and retained as internal partners, a process called endosymbiosis. This explains why chloroplasts have their own DNA and a thylakoid membrane system resembling that of cyanobacteria. The oxygen released by ancient cyanobacteria fundamentally changed the planet, building up the atmospheric oxygen that made complex aerobic life possible.

The bacterial evolutionary tree versus the "briar patch" model

The evolution of photosynthesis is difficult to draw as a simple branching tree because the genes for the process appear to have moved sideways between unrelated lineages. Rather than a clean evolutionary tree, some researchers describe early bacterial evolution as a tangled "briar patch," in which different metabolic pathways were assembled from genes shared across species. Work by Howard Gest and others, summarised by science writer Hal Kibbey at Indiana University, even suggested a reversal of the conventional assumption about which photosynthetic bacteria came first — proposing that purple and green bacteria represent some of the earliest photosynthetic organisms.

Gene-swapping in early bacterial evolution

Horizontal gene transfer — the swapping of genes between different bacterial species — played a central role in shaping early photosynthesis. Because the components of the photosynthetic apparatus could be passed between lineages independently, individual metabolic processes evolved and recombined separately, so that no single organism's family tree captures the full history of the trait. Molecular data analysis of these genes, including the comparative work led by Jin Xiong and Carl E. Bauer, supports the view that the reaction centres, pigments, and electron-transport components have intertwined and partly independent origins. Researchers such as William Fischer have continued to refine the timeline of when oxygen-producing photosynthesis arose.

Comparing photosynthesis and cellular respiration

Photosynthesis and cellular respiration are complementary, near-opposite processes that together cycle energy and carbon through the biosphere. Photosynthesis uses light energy to build carbohydrates from carbon dioxide and water and releases oxygen, while cellular respiration breaks carbohydrates back down using oxygen, releasing carbon dioxide, water, and usable energy in the form of ATP. The two share machinery and an evolutionary heritage — both rely on membrane-bound electron-transport chains — which is one reason the genes behind them are so deeply intertwined in early bacterial evolution.

The energy of photosynthesis on a global scale

On a global scale, photosynthesis is the largest capture of solar energy on Earth, storing far more energy each year than human civilisation consumes. This energy flow underpins agricultural production and crop yields, since the food we grow is stored photosynthetic energy, and it drives the carbon dioxide cycle that links the atmosphere, oceans, and living things. The same process is the source of fossil fuels — ancient buried biomass — and of modern biofuels such as ethanol made from corn and sugar cane, a major industry in countries like Brazil. Because photosynthesis removes carbon dioxide, it also moderates the build-up of greenhouse gases and is central to discussions of climate change.

The reach of photosynthesis into human technology is wide and growing:

• Food production: nearly all human and animal nutrition traces back to the carbohydrates plants synthesise.
• Fibre and materials: cellulose from plants supplies paper, textiles, and building materials.
• Biomass and biofuels: crops are converted into ethanol and other renewable fuels.
• Crop improvement: molecular biology and plant breeding aim to raise photosynthetic efficiency and yield, including by reducing photorespiration.
• Plant growth regulation: herbicides often work by blocking steps of photosynthesis or related plant processes.
• Solar energy harvesting: chemists such as Devens Gust have built artificial photosynthetic reaction centres that mimic the natural process to capture solar energy and store it chemically.

Conclusion

The study of photosynthesis traces an arc from Lomonosov's untested idea of air-feeding, through the sealed-jar experiments of Priestley and Ingenhousz, the carbon-nutrition insight of Senebier, the quantitative measurements of Saussure, and the energetic interpretation of Timiryazev, to the molecular phylogenetics of bacterial reaction centres. Along the way the very definition of photosynthesis expanded — from "restoring air" to "carbon assimilation in light" to the broad conversion of solar energy into chemical energy that today encompasses both oxygenic plants and the diverse anoxygenic bacteria. Understanding this process is not merely historical: it underlies food, fuel, fibre, the oxygen we breathe, and the search for clean energy through artificial photosynthesis.