Early Experiments On Photosynthesis: Experiments And Factors Affecting

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:57 PM IST

What Is Photosynthesis?

Photosynthesis is a process in which green plants, algae, and certain bacteria convert light energy into chemical energy and subsequently produce glucose and oxygen from carbon dioxide and water. The process, therefore, forms the basics of how energy flows through the food chain, for it forms the primary energy source for almost all life forms on Earth.

Early experiments by Joseph Priestley and Jan Ingenhousz in the 18th developed the fact that plants could be able to produce oxygen and that the process had to be completed under the presence of light. To this extent, studies of such nature laid the foundation for our understanding of photosynthesis. The ancient theories evidenced that photosynthesis was propped to play the most essential function in maintaining life on Earth and enabling the proper functioning of its ecosystems.

Ancient Theories Of Plant Growth

The ancient theories related to plant growth are:

Aristotle’s Theory

Aristotle was a Greek philosopher who theorized that plants grow out of the soil and also have some form of a soul that allows them to emerge and procreate. He showed his concepts of plants as passive animals that only absorb nourishment from the soil, where they have no idea about sunlight or other essentials' impact on them.

Theophrastus’ Observations

Theophrastus, Aristotle's student, vented much-entering botany by systematically monitoring the growth of plants. He noted several functions of plants, primarily on how different plants react to their surroundings. Still, it appears he didn't identify the role that sunlight played in photosynthesis. His contribution laid the building blocks for future botanical research and also led to the fact that empirical observations play a significant role in plant biology.

Van Helmont’s Experiment (1648)

Van Helmont decided to run an experiment on the measurement of plants' growth by water. He took a single willow tree, planted it in a pot, and weighed it, including both the tree and pot, with a known soil weight. Then, throughout five years, he added water to the pot but not additional soil.

Hypothesis And Objective

Van Helmont pointed out that the growth of plants is due to water intake but not soil or any other food matter. He carried out this experiment to find the contribution of water in increasing the growth and hence the weight of a plant.

Experiment Design

The details are given below:

Materials Used

A large pot with known weight soil
Young willow tree
Distilled water
Weighing balance of weighing the mass of the soil and pot
Various water and other maintenance tools for the plant

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Procedure

Weigh the pot and the soil
Plant the willow tree and weigh the pot with the tree.
Water the plant regularly with distilled water
After five years, re-weigh the weight of the pot the remaining soil and the weight of the tree.

Results And Conclusion

Van Helmont found that the willow tree's weight had increased tremendously, meanwhile, the weight of the soil had lost a little. Thereby giving him the reason to think that the gain in weight of the plant was total because of the water since the mass lost by the soil was meagre.

Weight Gain Of Plant

The willow tree grew and its weight increased considerably. His measurements showed that the increase in the weight of the tree was more, relative to the decrease in mass of the soil.

Role Of Water In Plant Growth

Van Helmont's experiment has been an early preliminary discovery of the fact that water is a vital element in plant growth. Unable to present the process of photosynthesis and cellular breathing, his findings insisted on the nature of water and, thus, opened the way for further studies related to the biology of plants and growth processes.

Joseph Priestley’s Experiments (1770s)

The details of the experiment are given below:

Hypothesis And Objective

Joseph Priestley had assumed that plants were able to return "foul" air to its normal condition, again suitable to sustain life. More particularly, he was trying to determine if plants would change the air in so doing, produce a substance in the air that was an essential requirement for respiration.

Experiment Design

Priestley designed an experiment to investigate how plants impact the purity of the air. He took a setup of a sealed container in which a plant with a lighted candle was put and observed a change in the flame in the candle in the presence of the plant and that would help him know if air is getting purified because of plants.

Materials Used

Glass jar or bell jar (sealed container)
A plant, for example, mint or other common window plants
A lit candle
A pair of bellows to add and remove air (optional)
Apparatus to measure and observe the flame

Procedure

Place a lit candle inside a sealed jar.
Put a plant in the jar and seal it so that no air inside can escape out to the atmosphere.
Observe the flame on the candle for some length of time recording changes in its nature and flicker.
After some time, take out the plant and examine the air by blowing out the candle again or using other ways.

Results And Conclusion

Priestley observed that a candle's flame, which became faint and extinguished in the sealed jar, would again be ignited if the plant was part of the equation. Therefore, the plant was releasing some combustible substance.

Priestley concluded that plants develop a principle (it would later be proven to be sensible people also inferred that since plants produced oxygen, then it was an unwholesome gas that harmed life.) This would be the same oxygen that purifies or renovates the atmosphere and that the plants serve as the food of the flame.

Discovery Of Oxygen

Although Priestley conceived of oxygen simply as a gas supporting combustion and respiration and did not consider it an element, his experiments greatly contributed to the discovery of oxygen. His work, at a minimum, thus laid the ground for many later discoveries concerning respiratory gases.

Role Of Plants In Air Purification

Priestley's experiments confirmed that plants clean the air by giving out oxygen and ridding the air of carbon dioxide. This discovery acknowledged the role of plants in providing breathable air and factored in later investigations into the part played by the process of photosynthesis in the quality of air and the state of health of ecosystems.

Jan Ingenhousz’s Discoveries (1779)

The details of the experiment are given below:

Hypothesis And Objective

Jan Ingenhousz hypothesised that green plants produce oxygen only in daylight and thus prepared to demonstrate how light is necessitated in the plant to produce oxygen and whether or not plants photosynthesise in the absence of light.

Jean Senebier’s Contributions (1782)

The details of the experiment are given below:

Hypothesis And Objective

Jean Senebier hypothesised that carbon dioxide is a critical factor for photosynthesis and that plants obtain this factor from the air. He aimed to determine how carbon dioxide functioned in the respiration and photosynthesis of plants.

Nicolas-Théodore de Saussure’s Findings (1804)

The details are given below:

Hypothesis And Objective

It was Nicolas-Théodore de Saussure who first proposed a hypothesis regarding plants: they neither do nor could solely absorb carbon dioxide. However, later he put forth a hypothesis that water could restructure via dissociation into hydrogen and oxygen, which in turn is used to build the plant biomass. His main goal was to assess the contributions of water and carbon dioxide toward the plant growth and formation of organic matter.

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Frequently Asked Questions (FAQs)

1. What was the significance of Van Helmont’s experiment on photosynthesis?

Van Helmont's experiment showed that plants increase in mass as a result of water intake, thus ruling out the theory that a large part of the increment in mass of a plant comes from the intake of soil.

2. How did Joseph Priestley contribute to the understanding of photosynthesis?

Joseph Priestley discovered that plants give off oxygen; this process is used in combustion and breathing, pointing out or stating that the role of the plants is to purify.

3. What did Jan Ingenhousz discover about photosynthesis?

Jan Ingenhousz discovered that light is an element needed for photosynthesis. This process is drawn out only by the green parts of a plant.

4. Why are Jean Senebier’s experiments important in the study of photosynthesis?

Experiments performed by Jean Senebier proved carbon dioxide to be another basic component of photosynthesis. He revealed that plants assimilate this gas and then use it for the formation of organic matter.

5. What were the key findings of Nicolas-Théodore de Saussure regarding photosynthesis?

Nicolas-Théodore de Saussure brought a better understanding of photosynthesis because Saussure quantified the roles of water and carbon dioxide in photosynthesis.

6. How did the discovery of cyanobacteria's role in the Great Oxygenation Event change our perspective on the evolution of photosynthesis?

The realization that cyanobacteria were responsible for the Great Oxygenation Event about 2.4 billion years ago highlighted the profound impact of photosynthesis on Earth's history. It showed that the evolution of oxygenic photosynthesis dramatically changed the planet's atmosphere and paved the way for the evolution of complex life forms. This discovery linked photosynthesis research to broader questions in Earth science and evolutionary biology.

7. What was the key finding of Jan Baptista van Helmont's willow tree experiment, and how did it advance our understanding of plant growth?

Van Helmont's willow tree experiment showed that the increase in the tree's mass over several years far exceeded the decrease in soil mass. This led him to conclude that water, not soil, was the primary source of the plant's growth. While his conclusion was not entirely correct (as we now know plants also use carbon dioxide from the air), this experiment was groundbreaking in challenging the prevailing belief that plants grew solely from nutrients in the soil.

8. What was the significance of Jan Ingenhousz's experiment in the history of photosynthesis research?

Jan Ingenhousz's experiment was crucial in demonstrating that light is essential for photosynthesis. He showed that plants produce oxygen only in the presence of light, not in darkness. This experiment helped establish the fundamental role of light in the photosynthetic process, laying the groundwork for further research into the light-dependent reactions of photosynthesis.

9. How did Joseph Priestley's experiments with a candle and a sprig of mint contribute to our understanding of photosynthesis?

Priestley's experiments demonstrated that plants can "refresh" air that has been depleted of oxygen by a burning candle. He observed that a mouse could survive in a sealed container with a mint plant, but not without it. This discovery suggested that plants produce a substance (later identified as oxygen) that is essential for animal life, hinting at the gas exchange aspect of photosynthesis.

10. What role did Cornelius van Niel's studies on purple sulfur bacteria play in elucidating the general equation for photosynthesis?

Van Niel's work with purple sulfur bacteria, which use hydrogen sulfide instead of water in photosynthesis, led him to propose a general equation for photosynthesis. He suggested that photosynthesis is essentially a light-dependent reaction in which hydrogen from a hydrogen donor reduces carbon dioxide to form carbohydrates. This insight helped scientists understand that oxygen released during photosynthesis comes from water, not carbon dioxide.

11. How did the discovery of RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) impact our understanding of carbon fixation in photosynthesis?

The discovery of RuBisCO, the enzyme responsible for the initial carbon fixation step in the Calvin cycle, was a major breakthrough. It explained how plants could capture and convert atmospheric CO2 into organic compounds. RuBisCO's dual function as both a carboxylase and oxygenase also helped scientists understand photorespiration, a process that can reduce photosynthetic efficiency under certain conditions.

12. How did the discovery of C4 photosynthesis by Hatch and Slack change our understanding of photosynthetic adaptations?

The discovery of C4 photosynthesis revealed an alternative carbon fixation pathway that some plants use to adapt to hot, dry environments. This pathway involves a spatial separation of initial carbon fixation and the Calvin cycle, allowing plants to concentrate CO2 around RuBisCO and reduce photorespiration. This finding expanded our understanding of plant adaptations to different environments and the diversity of photosynthetic mechanisms.

13. What was the significance of Daniel Arnon's discovery of photophosphorylation in chloroplasts?

Arnon's discovery of photophosphorylation demonstrated that chloroplasts can produce ATP using light energy, without the need for cellular respiration. This finding showed that chloroplasts are capable of generating their own energy currency, making them semi-autonomous organelles. It was a crucial step in understanding how light energy is converted into chemical energy during photosynthesis.

14. What was the significance of discovering the role of magnesium in chlorophyll molecules?

The discovery that magnesium is the central atom in chlorophyll molecules was crucial for understanding the structure and function of these pigments. Magnesium's ability to form coordination complexes allows chlorophyll to absorb light efficiently and initiate the electron transfer process in photosynthesis. This finding linked the atomic structure of chlorophyll to its function in light harvesting.

15. How did T.W. Engelmann's experiment with algae and bacteria demonstrate the relationship between light wavelength and photosynthesis?

Engelmann used a prism to split white light into its component colors and exposed different parts of a filamentous alga to these colors. He then added aerobic bacteria, which congregated near the portions of the alga exposed to red and blue light. This elegant experiment showed that photosynthesis is most efficient at red and blue wavelengths of light, corresponding to the absorption spectrum of chlorophyll.

16. How did the discovery of radioactive isotopes contribute to our understanding of the carbon fixation process in photosynthesis?

The use of radioactive carbon-14 isotopes allowed scientists to trace the path of carbon during photosynthesis. In particular, Melvin Calvin and his colleagues used C-14 to map out the steps of carbon fixation, leading to the discovery of the Calvin cycle. This technique revolutionized our understanding of the dark reactions of photosynthesis and how plants convert carbon dioxide into glucose.

17. What was the significance of Robert Hill's chloroplast experiment in the study of photosynthesis?

Hill's experiment demonstrated that isolated chloroplasts could produce oxygen in the presence of light and an artificial electron acceptor, even without carbon dioxide. This showed that the light-dependent reactions of photosynthesis (which produce oxygen) can occur independently of the carbon fixation reactions. Hill's work was crucial in separating the light and dark reactions of photosynthesis conceptually and experimentally.

18. How did the discovery of photosystems I and II contribute to our understanding of the light-dependent reactions of photosynthesis?

The discovery of photosystems I and II revealed that photosynthesis involves two distinct light-capturing systems working in series. This finding explained how plants can efficiently capture light energy and use it to drive electron transport, leading to the production of ATP and NADPH. Understanding these photosystems was crucial for elucidating the Z-scheme of electron flow in photosynthesis.

19. What role did Melvin Calvin's lollipop experiment play in unraveling the dark reactions of photosynthesis?

Calvin's lollipop experiment, using algae in a lollipop-shaped flask, allowed for rapid sampling and analysis of photosynthetic products at different time points. By exposing the algae to radioactive CO2 for varying durations and then quickly killing and analyzing them, Calvin and his team were able to trace the path of carbon through the photosynthetic process. This led to the discovery of the Calvin cycle, also known as the dark reactions or light-independent reactions of photosynthesis.

20. What was the significance of Otto Warburg's quantum yield experiments in photosynthesis research?

Warburg's quantum yield experiments aimed to determine the minimum number of light quanta required to fix one molecule of CO2 in photosynthesis. His work suggested that photosynthesis was highly efficient, requiring only 4-5 quanta per CO2 molecule. Although later research showed the actual number to be higher, Warburg's experiments were crucial in establishing the quantitative relationship between light absorption and carbon fixation in photosynthesis.

21. What role did the isolation of chloroplasts play in advancing photosynthesis research?

The isolation of intact chloroplasts allowed scientists to study photosynthetic reactions outside of the complex cellular environment. This technique enabled researchers to manipulate conditions and study specific aspects of photosynthesis, such as the light-dependent reactions, in a controlled setting. It was crucial for experiments like Hill's reaction and for understanding the biochemical pathways involved in photosynthesis.

22. How did the use of inhibitors contribute to our understanding of the electron transport chain in photosynthesis?

Inhibitors like DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) helped researchers identify specific components of the photosynthetic electron transport chain. By selectively blocking certain steps, scientists could determine the order of electron carriers and the points at which ATP and NADPH are produced. This approach was instrumental in mapping out the details of the light-dependent reactions.

23. How did the development of pulse-amplitude-modulated (PAM) fluorometry contribute to studying photosynthesis in living plants?

PAM fluorometry allowed scientists to measure photosynthetic efficiency in living plants without damaging them. This technique measures chlorophyll fluorescence, which is inversely related to photosynthetic activity. It enabled researchers to study how various environmental factors affect photosynthesis in real-time and in intact plants, providing valuable insights into plant physiology and stress responses.

24. What role did the discovery of photorespiration play in our understanding of RuBisCO's function and plant productivity?

The discovery of photorespiration explained why plant productivity was often lower than theoretically predicted. It revealed that RuBisCO can fix oxygen instead of CO2 under certain conditions, leading to energy loss. This finding was crucial for understanding plant metabolism under different environmental conditions and led to research on ways to reduce photorespiration to improve crop yields.

25. How did the elucidation of the xanthophyll cycle contribute to our understanding of plants' photoprotection mechanisms?

The xanthophyll cycle was found to be a key mechanism for plants to dissipate excess light energy as heat, protecting them from photodamage. This discovery helped explain how plants adapt to varying light conditions and maintain photosynthetic efficiency while avoiding damage from excess light. It broadened our understanding of the complex regulatory mechanisms involved in photosynthesis.

26. How did the development of artificial photosynthesis systems contribute to our understanding of natural photosynthesis?

Attempts to create artificial photosynthesis systems have provided insights into the fundamental principles of light harvesting, electron transfer, and catalysis in natural photosynthesis. These studies have helped identify the key components and processes that make natural photosynthesis so efficient, while also suggesting potential improvements for artificial systems designed for energy production.

27. How did the use of electron microscopy advance our understanding of chloroplast structure and function?

Electron microscopy revealed the detailed internal structure of chloroplasts, including the arrangement of thylakoid membranes into grana and stroma lamellae. This structural information was crucial for understanding how the spatial organization of photosynthetic components contributes to their function, such as the separation of photosystems I and II in different regions of the thylakoid membrane.

28. What was the significance of discovering the light-harvesting complex proteins (LHCs) in photosynthesis research?

The discovery of LHCs explained how plants can efficiently capture light energy across a broad spectrum. These proteins, associated with chlorophyll molecules, form antenna complexes that funnel light energy to the reaction centers of photosystems. Understanding LHCs was crucial for explaining how plants maximize light capture and adapt to different light environments.

29. How did the development of chlorophyll fluorescence techniques contribute to studying photosynthesis in vivo?

Chlorophyll fluorescence techniques allowed researchers to non-invasively measure photosynthetic efficiency in living plants. These methods provide real-time information about the state of photosystem II and the overall health of the photosynthetic apparatus. They have become invaluable tools for studying plant stress responses and for screening crop varieties for improved photosynthetic performance.

30. How did the elucidation of the Calvin cycle's regulation mechanisms contribute to our understanding of photosynthetic carbon fixation?

Understanding the regulation of the Calvin cycle, including the roles of light-activated enzymes and metabolite feedback, revealed how plants balance carbon fixation with their energy status and metabolic needs. This knowledge explained how plants coordinate the light-dependent and light-independent reactions of photosynthesis and adapt to changing environmental conditions.

31. What role did the discovery of state transitions play in explaining how plants optimize light harvesting?

State transitions were found to be a mechanism by which plants can balance the excitation of photosystems I and II under changing light conditions. This process involves the movement of light-harvesting complexes between the two photosystems, allowing plants to optimize their light-harvesting efficiency. The discovery highlighted the dynamic nature of the photosynthetic apparatus and its ability to adapt to varying light qualities.

32. How did the development of transgenic plants contribute to photosynthesis research?

Transgenic plants allowed researchers to manipulate specific genes involved in photosynthesis, providing insights into their functions and the potential for improving photosynthetic efficiency. For example, plants with altered levels of RuBisCO or other Calvin cycle enzymes have been used to study carbon fixation and explore strategies for enhancing crop productivity.

33. What was the significance of discovering the role of stomata in regulating CO2 uptake and water loss in photosynthesis?

The discovery of stomata's role in gas exchange revealed how plants balance CO2 uptake for photosynthesis with water loss through transpiration. This finding was crucial for understanding how plants adapt to different environmental conditions and manage their water use efficiency. It also highlighted the complex interplay between photosynthesis and other plant physiological processes.

34. What role did the elucidation of the water-splitting complex play in understanding oxygen evolution in photosynthesis?

The discovery of the manganese-containing water-splitting complex in photosystem II explained how plants are able to oxidize water molecules to produce oxygen. This finding was crucial for understanding the source of oxygen in photosynthesis and the mechanism by which plants generate the electrons needed for the light-dependent reactions.

35. How did the development of high-resolution structural biology techniques contribute to our understanding of photosynthetic complexes?

Techniques like X-ray crystallography and cryo-electron microscopy have revealed the detailed structures of photosynthetic complexes such as photosystems I and II, the cytochrome b6f complex, and ATP synthase. These structural insights have been crucial for understanding how these complexes function at the molecular level, including the precise arrangements of pigments, electron carriers, and protein subunits.

36. What was the significance of discovering the role of the circadian clock in regulating photosynthesis?

The discovery that the circadian clock regulates many aspects of photosynthesis, including gene expression and enzyme activities, revealed how plants anticipate and prepare for daily light-dark cycles. This finding explained how plants optimize their photosynthetic performance throughout the day and adapt to seasonal changes in day length.

37. What role did the discovery of chemiosmosis play in explaining ATP synthesis during photosynthesis?

Peter Mitchell's chemiosmotic theory explained how the electron transport chain in photosynthesis generates a proton gradient across the thylakoid membrane. This gradient drives ATP synthesis through ATP synthase, much like in cellular respiration. This discovery provided a unifying mechanism for energy production in both photosynthesis and respiration, revolutionizing our understanding of bioenergetics.

38. What role did the discovery of carbon concentrating mechanisms in algae and cyanobacteria play in understanding photosynthetic adaptations?

The discovery of carbon concentrating mechanisms revealed how some photosynthetic organisms adapt to low CO2 environments. These mechanisms, which involve actively concentrating CO2 around RuBisCO, showed that photosynthetic organisms have evolved diverse strategies to optimize carbon fixation. This finding was important for understanding photosynthesis in aquatic environments and has implications for improving crop productivity.

39. What was the significance of discovering the role of carotenoids in photoprotection and light harvesting?

The discovery that carotenoids serve both as accessory pigments for light harvesting and as photoprotective agents expanded our understanding of the complexity of the photosynthetic apparatus. Carotenoids' ability to quench excited chlorophyll molecules and dissipate excess energy as heat is crucial for protecting plants from photodamage, especially under high light conditions.

40. How did the discovery of C3-C4 intermediate species contribute to our understanding of the evolution of photosynthetic pathways?

The identification of plants with characteristics intermediate between C3 and C4 photosynthesis provided insights into how the C4 pathway might have evolved. These species showed various stages of the development of C4 traits, suggesting that the evolution of C4 photosynthesis occurred gradually through a series of adaptive steps. This discovery has implications for understanding plant evolution and for efforts to engineer C4 traits into C3 crops.

41. How did the discovery of non-photochemical quenching (NPQ) mechanisms contribute to our understanding of photoprotection in plants?

The elucidation of NPQ mechanisms showed how plants dissipate excess light energy as heat to protect their photosynthetic apparatus from damage. This discovery was crucial for understanding how plants cope with fluctuating light conditions and maintain photosynthetic efficiency while avoiding photodamage. It also provided insights into potential strategies for improving crop resilience to environmental stresses.