The History of Photosynthesis Study: From Priestley to the Modern Equation
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Photosynthesis is the process by which green plants, algae, and certain bacteria convert light energy into chemical energy, building organic compounds from carbon dioxide and water while releasing oxygen. It underpins almost all life on Earth: it supplies the food chain with energy, fills the atmosphere with breathable oxygen, and locks atmospheric carbon into living matter. The scientific study of photosynthesis began in the mid-18th century and has grown into one of the central subjects of plant physiology, biochemistry, and evolutionary biology.
История изучения фотосинтеза: краткий обзор
The history of photosynthesis research stretches from the mid-1700s to the present and represents a chain of experiments that gradually revealed how plants feed on air and light. Early investigators established that plants take in carbon dioxide, give off oxygen, and require both light and the green pigment chlorophyll. Later researchers explained the energetics of the process, identified its pigments, and finally separated photosynthesis into distinct light-dependent and light-independent stages. Studying how this knowledge accumulated is itself a clear example of how plant physiology matured as a science.
The decisive early contributors form a recognizable sequence: Jan Baptist van Helmont weighed plant growth against soil and water; Joseph Priestley showed that plants restore "spoiled" air; Jan Ingenhousz proved that light is required; Jean Senebier identified carbon nutrition; and Nicolas-Théodore de Saussure measured the gases quantitatively. Each step is described in detail in the sections below.
Понятие о фотосинтезе
Фотосинтезом называется первичный синтез органических веществ из углекислого газа и воды, протекающий в тканях зеленых растений с использованием энергии света, которая при этом превращается в потенциальную химическую энергию органических веществ. Этот процесс выражают суммарным уравнением: 6СО2+6Н2 О + (энергия света (686 ккал)/хлорофилл) = С6Н12О6+6О2
Photosynthesis, then, is the primary synthesis of organic matter from carbon dioxide and water, carried out in the tissues of green plants using light energy that is converted into the potential chemical energy of organic compounds. The process is highly complex and consists of a whole series of biophysical and biochemical reactions rather than a single chemical step.
Using solar energy absorbed by chlorophyll, plants rearrange molecules of CO2 and H2O, reducing carbon and converting it from an inorganic compound into an organic one, while releasing oxygen.
The organic substances synthesized by green plants, and the energy stored within them, are the principal sources of matter and energy used by all other organisms in the course of their lives (подробнее: Чем полезен лес).
The dry matter of plants is almost half carbon. If carbon dioxide is removed from the atmosphere, plants stop accumulating organic matter and soon die. Carbon dioxide is therefore essential for normal plant growth, and plants obtain it from the air. By volume, carbon dioxide makes up about 0.03% of the atmosphere.
Определение и переопределение термина «фотосинтез»
The definition of photosynthesis has been revised repeatedly as scientists learned more about the underlying chemistry. The classic definition treats it as the light-driven production of carbohydrates from carbon dioxide and water with the release of oxygen. This narrow definition, however, describes only oxygenic photosynthesis — the kind performed by plants, algae, and cyanobacteria.
A broader modern definition is needed because many photosynthetic bacteria do not produce oxygen and do not use water as their electron donor. Organisms also differ in how they use light: photoautotrophs build all their organic matter from carbon dioxide using light energy, while photoheterotrophs use light for energy but rely on organic compounds as a carbon source. The discovery of photophosphorylation — the light-driven synthesis of ATP — pushed scientists to define photosynthesis fundamentally as the conversion of light energy into chemical energy, with carbon fixation as a frequent but not universal consequence.
Химическое уравнение и превращение энергии
The overall chemical equation of oxygenic photosynthesis summarizes a transformation of energy as much as a transformation of matter. Six molecules of carbon dioxide and six of water, driven by roughly 686 kilocalories of light energy captured by chlorophyll, yield one molecule of glucose and six molecules of oxygen:
6CO2 + 6H2O + light energy → C6H12O6 + 6O2
This equation captures the essence of energy conversion in photosynthesis: diffuse solar radiation becomes concentrated, stable chemical energy stored in the bonds of carbohydrates. The water molecule is the source of the released oxygen, while the carbon dioxide supplies the carbon skeleton of the sugar. Cornelis van Niel later generalized this scheme, showing that the equation is one special case of a wider family of reactions in which various electron donors replace water.
Использование солнечной энергии как элемент процесса фотосинтеза
Solar energy is the engine of photosynthesis, and capturing it is the first and most distinctive stage of the whole process. Plants do not use heat from sunlight directly; instead, pigment molecules absorb light of specific wavelengths and pass the captured energy into a chain of reactions that ultimately stores it in chemical bonds. The efficiency and limits of this capture set the ceiling on how much organic matter the biosphere can produce.
Энергетика фотосинтеза и мировая статистика
Photosynthesis is the largest energy-capturing process on the planet, fixing energy on a scale that dwarfs all human technology combined. Through photosynthesis, the world's plants, algae, and cyanobacteria convert solar energy into the chemical energy of biomass that feeds nearly every food chain. The same process, acting over geological time, produced the fossil fuels — coal, oil, and natural gas — that power modern civilization, since these are the buried remains of ancient photosynthetic organisms.
Because photosynthesis is the original source of food, fiber, and fuel, even small improvements in its efficiency have enormous practical value. Researchers studying solar energy harvesting technology look to photosynthesis as a model for capturing sunlight, and some build artificial photosynthetic reaction centers that mimic how plants split molecules and store energy. Devens Gust and colleagues, for example, have constructed synthetic molecular assemblies designed to imitate the light-capturing core of natural photosynthesis.
Хлорофилл и поглощение света
Chlorophyll is the green pigment that absorbs the light energy used in photosynthesis, and its absorption properties explain why most plants are green. Chlorophyll strongly absorbs red and blue light while reflecting green, which is why foliage appears green to the eye. The light spectrum therefore matters directly: only the wavelengths a pigment can absorb can drive the reaction.
Plants and photosynthetic organisms use several pigments to broaden the range of usable light. Alongside the chlorophylls, accessory pigments such as the carotenoids capture additional wavelengths and hand the energy on to chlorophyll. Theodor Engelmann demonstrated the link between the light spectrum and photosynthesis in an elegant 19th-century experiment: using the filamentous alga Spirogyra and oxygen-seeking bacteria as living detectors, he showed that the bacteria clustered where red and blue light struck the alga — precisely the wavelengths chlorophyll absorbs most strongly. This use of bacteria for photometry tied the action spectrum of photosynthesis directly to the absorption spectrum of chlorophyll.
Ранние этапы изучения фотосинтеза (XVIII–XIX вв.)
The foundations of photosynthesis science were laid during the 18th and early 19th centuries through a connected series of experiments on plants and air. In this period researchers established that plants absorb carbon dioxide, release oxygen, require light and chlorophyll, and build carbon-rich dry matter. The story begins even earlier, with a famous experiment on where a plant's mass comes from.
Jan Baptist van Helmont, in the 17th century, performed one of the first quantitative plant experiments by growing a willow tree in a weighed amount of soil for five years. The willow gained about 74 kilograms while the soil lost almost nothing, leading van Helmont to conclude — incorrectly but influentially — that the new plant matter came from water alone. His experiment was important because it framed the central question that later researchers answered: where does plant biomass actually come from?
М. В. Ломоносов о воздушном питании растений
М. В. Ломоносов (1761 г.) first proposed the idea that plants feed on air, though he had no experimental evidence to support it. His insight anticipated, in principle, the later discovery that the carbon in plant matter is drawn from atmospheric carbon dioxide.
Опыты Д. Пристли
Joseph Priestley conducted the first study of how plants affect the surrounding air in 1773 using sealed glass jars. 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 have spoiled.
What escaped Priestley in his first experiments was that this restoration of the air happens only in the light.
Working later, Joseph Priestley and Jan Ingenhousz (1779) established that plants can purify air only in the light, while in darkness they spoil it just as animals do. This air-restoring activity belongs only to the green parts of the plant. These experiments produced the first evidence that plants carry out two directly opposing processes affecting air composition — what would later be recognized as photosynthesis and respiration — although neither Priestley nor Ingenhousz grasped what this "restoration" of air meant for the plant itself.
Открытие кислорода как отдельного газа
The recognition of oxygen as a distinct gas was the breakthrough that gave Priestley's plant experiments their full meaning. Joseph Priestley himself isolated the gas in 1774, and Antoine-Laurent Lavoisier soon explained its true role, naming it oxygen and overturning the old "phlogiston" theory of combustion and respiration. Once chemists understood that animals consume oxygen and that this is the very gas plants release in the light, the connection between respiration and photosynthesis became clear.
Identifying oxygen as a discrete chemical species let researchers describe the plant gas exchange in precise terms: green tissues take up carbon dioxide and give off oxygen in light. This single advance in chemistry transformed a set of curious observations into a measurable physiological process.
Опыты И. Ингенгауза и роль света
Jan Ingenhousz proved that light is the essential driver of the air-purifying process in plants, sharpening Priestley's earlier and partly contradictory findings. In 1779 Ingenhousz showed that only the green parts of a plant restore the air, and only when illuminated; the same plants in darkness, like animals, consume oxygen and release carbon dioxide. He thereby distinguished the light-requiring process of photosynthesis from the continuous process of respiration.
Ingenhousz's emphasis on light was the crucial conceptual step that earlier workers had missed. By tying the beneficial activity of plants specifically to sunlight, he established light as a necessary input alongside carbon dioxide, laying the groundwork for later studies of how light energy is captured and used.
Ж. Сенебье о процессе углеродного питания
Jean Senebier (1782) demonstrated that the uptake of carbon dioxide and release of oxygen by plants in the light is a process of carbon nutrition, through which carbon accumulates in the plant. Senebier was the first to give a correct explanation of the essence of plant gas exchange, linking the gases consumed and released to the building of the plant's own substance.
Синтез углеродных соединений из углекислоты
Senebier's key insight was that the carbon in new plant matter comes from carbonic acid — that is, from dissolved carbon dioxide — and not from the soil. He showed that water containing dissolved carbon dioxide, when exposed to light in the presence of green tissue, supports the synthesis of organic carbon compounds and the release of oxygen. This established carbon dioxide as the raw material from which plants construct their carbon skeletons, directly confirming Lomonosov's earlier intuition about air nutrition and explaining why removing carbon dioxide halts plant growth.
Опыты Н. Соссюра
This series of discoveries in the field of photosynthesis culminated in the experiments of Nicolas-Théodore de Saussure (1804), who showed quantitatively that the volumes of the exchanged gases — oxygen and carbon dioxide — are equal in this process, and that water is consumed along with carbon dioxide, because the gain in the dry weight of the plant considerably exceeded the weight of carbon contained in the absorbed carbon dioxide.
In this way the origin of the carbon, oxygen, and hydrogen in plants was established.
Thus, over the course of the 18th and the beginning of the 19th centuries, the basic principles of the air nutrition of plants 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. What the role of light actually was, however, remained unclear.
К. А. Тимирязев и энергетическая сторона фотосинтеза
The next stage in understanding the nature of photosynthesis was K. A. Timiryazev's study of the energetics of the process and the role of light. Timiryazev 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 photosynthesis.
Major contributions to the study of the pigments involved in photosynthesis were made by:
- Willstätter, who gave the formula for chlorophyll and the каротиноидов,
- M. S. Tsvet, who developed the chromatographic method for separating leaf pigments.
The ecology of photosynthesis was studied by many Russian scientists:
- S. P. Kostychev,
- V. N. Lyubimenko,
- A. A. Ivanov,
- D. I. Ivanovsky,
- A. A. Richter.
Major contributions to the chemistry of photosynthesis were made by Soviet scientists:
- A. I. Terenin,
- A. A. Krasnovsky,
- A. A. Nichiporovich,
- T. N. Godnev,
and abroad by:
- O. Warburg,
- M. Calvin,
- E. I. Rabinowitch and others.
Опыты Блэкмана о свете и температуре
Frederick Blackman's experiments around 1905 revealed that photosynthesis consists of two distinct kinds of reactions — one that depends on light and one that does not. Blackman found that at low light intensity the rate of photosynthesis increased with more light but was largely unaffected by temperature, whereas at high light intensity the rate rose with temperature instead. He reasoned that a fast, light-driven photochemical step is followed by a slower, temperature-sensitive chemical step.
This interpretation established the two-stage model of photosynthesis: a light-dependent phase and a "dark," temperature-controlled phase governed by enzymes. Blackman's work explained why factors like light, temperature, and carbon dioxide can each become the limiting factor under different conditions, and it framed the modern division of photosynthesis into light reactions and carbon-fixing reactions.
История термина «фотосинтез»
The word "photosynthesis" itself has a documented history that mirrors the maturing of the science. The process was studied for more than a century before it acquired its now-standard name, and the choice of term was the subject of genuine debate among scientists. Tracing the terminology shows how vocabulary in the biological sciences evolves to match new understanding.
Чарльз Барнс и предложение термина «фотосинтез»
Charles Barnes, an American botanist, proposed a formal name for the process of carbon assimilation in green plants in 1893. Barnes actually suggested two candidate terms, "photosyntax" and "photosynthesis," and personally favored "photosyntax." The scientific community, however, gradually adopted "photosynthesis" instead, and that is the term recorded and preserved in the literature, including in the Oxford English Dictionary.
Эволюция научной терминологии
The photosyntax-versus-photosynthesis episode is a clear case of semantic evolution in the biological sciences, where the term that prevails is not always the one its proposer preferred. "Photosynthesis," built from the Greek roots for "light" and "putting together," proved intuitive and durable, while "photosyntax" faded from use. As later discoveries — such as anoxygenic bacterial photosynthesis and photophosphorylation — broadened what the process encompassed, the meaning attached to the surviving word expanded rather than being replaced, illustrating how scientific terminology adapts to accommodate new knowledge.
Структура хлоропласта и его ультраструктура
In plants and algae, photosynthesis takes place inside specialized organelles called chloroplasts. A chloroplast is bounded by a double membrane and contains an internal system of flattened membranous sacs called thylakoids, often stacked into structures known as grana, all suspended in a fluid matrix called the stroma. This compartmentalized ultrastructure physically separates the two stages of photosynthesis.
The thylakoid membranes house the chlorophyll and the protein complexes that carry out the light-dependent reactions, while the surrounding stroma contains the enzymes that fix carbon in the light-independent reactions. The leaf is itself adapted to support this organelle: broad, flat blades expose a large surface to sunlight, while internal air spaces and pores (stomata) allow carbon dioxide to reach the chloroplast-rich cells. This arrangement, from leaf shape down to thylakoid stacking, optimizes the capture of light and the supply of raw materials.
Эволюция фотосинтеза
Photosynthesis is an ancient process whose origins lie in bacteria that lived billions of years ago, long before plants existed. Studying its evolution combines molecular biology, comparative analysis of genes, and the fossil record. Modern molecular data have produced surprising conclusions about which organisms invented photosynthesis and how the machinery spread from one lineage to another.
Древние фотосистемы у бактерий
The earliest photosystems — the protein-pigment complexes that capture light — first arose in bacteria, not in plants. These ancient reaction centers performed anoxygenic photosynthesis, meaning they captured light energy without splitting water and without releasing oxygen. The two main types of photosystem found today in cyanobacteria and plants are thought to descend from these primitive bacterial reaction centers, which were later combined and refined into the oxygen-producing apparatus.
Открытие аноксигенных фотосинтезирующих бактерий
Anoxygenic photosynthetic bacteria are organisms that perform photosynthesis without producing oxygen, and their discovery reshaped the understanding of the process. Cornelis van Niel was central to this work: by studying purple and green sulfur bacteria, he showed that these microbes use compounds such as hydrogen sulfide instead of water as their electron donor, releasing sulfur rather than oxygen. His comparative studies led to the unifying insight that oxygenic and anoxygenic photosynthesis are variations on a single underlying chemical theme.
Варианты бактериального фотосинтеза
Bacteria carry out several distinct variants of photosynthesis, classified largely by whether they produce oxygen and which pigments and electron donors they use. The main groups include:
- Purple bacteria and green bacteria, which perform anoxygenic photosynthesis using bacteriochlorophyll;
- Cyanobacteria, which perform oxygenic photosynthesis using chlorophyll and water as the electron donor;
- Heliobacteria, anoxygenic bacteria with their own distinctive type of photosystem;
- Halobacterium and related organisms, which use the pigment bacteriorhodopsin to capture light by a completely different, non-chlorophyll mechanism.
The non-chlorophyll system of Halobacterium is striking because bacteriorhodopsin drives a light-powered proton pump rather than the classic electron-transport photosynthesis, showing that nature has solved the problem of capturing light energy in more than one way.
Эволюционное положение гелиобактерий
Heliobacteria occupy a key position in studies of photosynthetic evolution because their reaction center is regarded as one of the simplest and possibly most ancient. Molecular analysis of heliobacteria has helped researchers reconstruct how the more complex photosystems of cyanobacteria and plants may have arisen from simpler ancestral forms. Their study by groups including Howard Gest at Indiana University placed heliobacteria firmly within debates about the deep origins of photosynthesis.
Обмен генами на ранних этапах эволюции бактерий
Gene-swapping — the horizontal transfer of genes between different bacterial lineages — appears to have shaped the early evolution of photosynthesis. Molecular work by Jin Xiong and Carl E. Bauer, reported in the journal Science, analyzed photosynthesis genes across bacterial groups and concluded that these genes did not descend along a single neat line. Instead, early bacteria exchanged blocks of photosynthetic genes, assembling the modern photosynthetic toolkit from components that originated in different organisms.
Эволюционное древо бактерий против модели «заросли»
Because of extensive gene-swapping, the early evolution of photosynthetic bacteria looks less like a clean branching tree and more like a tangled "briar patch." In the conventional view, each metabolic process is inherited down a single evolutionary tree, but the gene-transfer findings suggest that individual metabolic capabilities, including photosynthesis, evolved and spread somewhat independently of the organisms that carried them. Work discussed by researchers such as William Fischer and summarized for the public by science writers like Hal Kibbey emphasized that reconstructing this history requires tracing individual genes rather than assuming whole organisms evolved as units. The journal Photosynthesis Research has been one venue for these evolutionary debates.
One striking implication is a partial reversal of the conventional view of which bacteria came first. Rather than oxygen-producing cyanobacteria being primitive, the molecular evidence supports the idea that anoxygenic purple and green bacteria were among the earliest photosynthetic organisms, with oxygen-producing photosynthesis evolving later as a more advanced innovation.
От цианобактерий к хлоропласту
The chloroplasts of plants and algae are descended from free-living cyanobacteria that were engulfed by a larger host cell and retained as internal partners. According to this endosymbiotic origin, an ancient cell took up an oxygen-producing cyanobacterium, which over time became the chloroplast — an organelle that still carries its own DNA and resembles cyanobacteria in many features. This event transferred oxygenic photosynthesis from bacteria into the eukaryotic lineages that gave rise to algae and, ultimately, all green plants.
Современное понимание фотосинтеза
Modern science describes photosynthesis as two coupled stages: the light-dependent reactions and the light-independent reactions, exactly as Blackman's experiments first suggested. Together these stages convert light energy into the chemical energy of carbohydrates. Understanding both stages, and how photosynthesis relates to respiration, is essential to applying this knowledge in agriculture and biotechnology.
The light-dependent reactions occur in the thylakoid membranes and capture light energy to produce the energy carriers ATP and NADPH, splitting water and releasing oxygen in the process. This light-driven synthesis of ATP is called photophosphorylation. The light-independent reactions, also called the Calvin cycle, then take place in the stroma, where enzymes use the ATP and NADPH to fix carbon dioxide. In this carbon-fixation step, carbon dioxide is attached to the five-carbon sugar ribulose bisphosphate, beginning the chain of enzymatic reactions that builds sugar.
Фотосинтез и клеточное дыхание
Photosynthesis and cellular respiration are complementary, nearly opposite processes that together cycle carbon and energy through the biosphere. Photosynthesis uses light energy to build carbohydrates from carbon dioxide and water while releasing oxygen; cellular respiration breaks those carbohydrates back down using oxygen, releasing carbon dioxide, water, and usable energy. The early experiments of Priestley and Ingenhousz first hinted at this balance when they found that plants restore air in the light but spoil it in the dark, behaving like animals when they cannot photosynthesize.
Образование углеводов
The direct product of carbon fixation is carbohydrate, which the plant uses for energy and as a building material. The Calvin cycle first produces simple sugars, which are then assembled into larger molecules. Among the most important products are:
- simple sugars such as glucose, used immediately for energy;
- starch, a storage form of carbohydrate;
- cellulose, the structural carbohydrate that forms plant cell walls and the basis of plant fiber materials.
Because cellulose and related carbohydrates are made by photosynthesis, the process is ultimately the source of wood, cotton, paper, and other fiber materials, as well as of food.
C4-фотосинтез
C4 photosynthesis is a specialized variant that helps certain plants fix carbon more efficiently under hot, bright, and dry conditions. In ordinary (C3) plants, the carbon-fixing enzyme can wastefully react with oxygen instead of carbon dioxide in a process called photorespiration, which lowers photosynthetic efficiency. C4 plants reduce this loss by first capturing carbon dioxide into a four-carbon compound and concentrating it around the carbon-fixing enzyme, suppressing photorespiration.
Crops such as corn and sugar cane use the C4 pathway, which is part of why they are so productive in warm climates. Understanding C4 photosynthesis and photorespiration is central to efforts in molecular biology and plant breeding aimed at raising photosynthetic efficiency in crops and increasing agricultural yields. Brazil's large-scale production of ethanol from sugar cane is one practical example of harnessing efficient photosynthesis for biofuel.
Значение фотосинтеза для жизни на Земле
Photosynthesis is fundamental to life on Earth because it supplies the food, oxygen, and stored energy on which almost all organisms depend. Green plants and other photosynthetic organisms are the primary producers at the base of nearly every food chain, and the organic matter they create feeds animals, fungi, and most bacteria. Without photosynthesis the accumulation of organic matter would stop and complex life could not persist.
The process also created and maintains the oxygen-rich atmosphere that animals breathe. The oxygen released by oxygenic photosynthesis, first by ancient cyanobacteria and now by plants and algae, transformed the early atmosphere and made aerobic life possible. At the same time, photosynthesis is central to the planet's carbon balance: it removes carbon dioxide from the air and locks it into biomass, which directly affects the concentration of greenhouse gases and influences climate change. Forests and other vegetation act as major carbon sinks, which is one reason their conservation matters so much (подробнее: Чем полезен лес is referenced above).
Photosynthesis carries great practical importance as well. It underlies food production and crop yields, supplies biomass and biofuels, and provides the raw material for fiber and many industrial products. It even shapes how people manage plant growth: herbicides often work by blocking steps in photosynthesis, killing weeds while crops are protected. From global oxygen supply to the bread on the table, photosynthesis remains the single most important biochemical process supporting life on Earth.
