Early Experiments On Photosynthesis: Experiments And Factors Affecting

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 forms the basics of how energy flows through the food chain, 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 can produce oxygen and the process had to be completed under the presence of light. Such studies 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 did not 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 ran 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.

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.

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

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 soil and the weight of the tree.

Observation & Conclusion

Van Helmont found that the weight of the willow tree had increased tremendously, while the soil had lost a little weight. 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:

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 doing so, producing 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.

Observation & Conclusion

Priestley observed that a candle's flame became faint and extinguished in the sealed jar, and would again ignite 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)

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.

He took green plants and submerged them under water in sunlight and darkness. He observed that bubbles formed only in the sunlight. It can be concluded from the experiment that oxygen is released only in the presence of sunlight. There only green parts of plants perform the process of photosynthesis.

Jean Senebier’s Contributions (1782)

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)

Nicolas-Théodore de Saussure first proposed that plants 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.

Summary Table – Early Experiments On Photosynthesis

The table below summarizes the early experiments on photosynthesis performed by different scientists:

Importance Of Early Experiments

The importance of early experiments includes:

• It establishes the scientific basis of photosynthesis.

• It showed that light, water and carbon dioxide are essential for the process of photosynthesis.

• It explained how plants sustain life by producing oxygen.

• It formed the basis for modern day plant physiology

Photosynthesis Experiments NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Experiments and their observations by different scientists

• Importance of experiments

Practice Questions for NEET

Q1. Which of the following is correct for photosynthesis?

1. Biological oxidation process

2. Photochemical catabolic process

3. Photo-oxidative metabolism

4. Biological photo metabolism

Correct answer: 4) Biological photo metabolism

Explanation:

Photosynthesis is the vital biological process through which green plants, algae, and certain bacteria transduce light energy to chemical energy, primarily in chloroplasts. This conversion yields glucose.

The fundamental equation of photosynthesis is:

6 CO₂ + 6 H₂O + light energy ↦ GLUCOSE + 6 O₂

Key components of this reaction are:

1. Carbon dioxide (CO₂) - Obtained from the atmosphere via stomata.
2. Water (H₂O) - Absorbed from the soil by roots.
3. Light energy - Captured by chlorophyll pigments in leaves.
4. Glucose - Utilized for energy and cellular expansion.
5. Oxygen (O₂) - Released into the atmosphere as a byproduct.

This process is essential for life on Earth, as it generates oxygen and organic compounds necessary for the survival of most organisms.

Hence, the correct answer is Option (4) Biological photo metabolism.

Q2. Oxygen is not produced during photosynthesis by

1. Cycas

2. Nostoc

3. Green sulphur bacteria

4. Chara

Correct answer: 3) Green sulphur bacteria

Explanation:

Photosynthesis -

Enzyme-regulated anabolic process of manufacture of organic compounds inside the chlorophyll-containing cells.

Since Charan Cycas come under the plant kingdom, they perform oxygenic photosynthesis. Green sulfur bacteria utilize H2S instead of H2O and perform anoxygenic photosynthesis or do not evolve oxygen.

Hence, the correct answer is Option (3) Green sulfur bacteria.

Q3. Greatest proportion of photosynthesis in the world is carried out by:

1. trees in the rain forests of the world

2. trees in the temperate forests of the world

3. algae in oceans

4. irrigated crop fields

Correct answer: 3) Algae in oceans

Explanation:

Algae are the largest oxygen-producers in the world through photosynthesis, in the oceans, and these organisms are very significant in the production of oxygen. Estimates have suggested that marine plants, particularly unicellular photosynthetic algae, produce about 70% to 80% of the oxygen produced in the atmosphere. These kinds of organisms, such as Prochlorococcus, play an important role in the aquatic ecosystem and, because of photosynthesis, play a crucial role in affecting the balance of oxygen in the environment.

Hence, the correct answer is Option (3) algae in oceans.

Also Read:

• MCQs on Photosynthesis

• Photosynthesis in Higher Plants

• Difference between Photosystem 1 and 2

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