Metabolism and Energy Transformation in Body Cells - Renata Armenakovna Petrosova 2004

Primary Synthesis of Organic Compounds. Photosynthesis
History of the Study of Photosynthesis

For centuries, biologists have tried to unlock the mystery of the green leaf. For a long time, it was believed that plants synthesize nutrients from Water and minerals. This conviction stemmed from an experiment conducted in the 17th century by the Dutch scientist Jan Baptist van Helmont. He planted a willow sapling in a tub, precisely recording its mass at 2.3 kg and the dry soil mass at 90.8 kg. For five years, he only watered the plant without adding anything to the soil. After five years, the tree's mass had increased by 74 kg, whereas the soil mass had decreased by a mere 0.06 kg. Van Helmont concluded that the plant derived all its substance from water. Thus, the scientist identified one of the substances essential for plant Photosynthesis.

The first attempt to scientifically define the function of the green leaf was undertaken in 1667 by the Italian naturalist Marcello Malpighi, the founder of plant anatomy. He noticed that if the initial cotyledons of pumpkin seedlings were removed, the plant would cease to develop. Malpighi hypothesized that under METABOLISM/18.html">The Influence of sunlight, certain transformations occurred within the plant's leaves, accompanied by the evaporation of water. However, these hypotheses did not attract much attention.

A century later, the Geneva scientist Charles Bonnet observed a curious phenomenon: plant leaves submerged in water and exposed to sunlight became covered with air bubbles. Bonnet sought to determine whether the air originated from the plants or the water. He conducted an experiment: taking a Glass of boiled water—which therefore contained no air—he placed plant leaves inside it. No bubbles appeared. From this, the scientist concluded that the bubbles were released not from the leaves, but from the water. Bonnet then modified the experiment. By blowing into the water several times through a delivery tube, he noticed that the bubbles began to appear once more. Bonnet concluded that the plant played no significant role in bubble formation, and that the bubbles merely gathered on the leaf surface from the water. This Conclusion proved to be incorrect.

The Discovery of the green leaf's role in photosynthesis belongs to the English chemist Joseph Priestley. In 1772, while studying Structure/19.html">The Importance of air for combustion and Respiration, he set up the following experiment. Under a glass bell jar where a candle had extinguished, he placed a mint plant and left it for some time. The plant did not die; on the contrary, it produced new leaves. When the scientist introduced a burning splint into the jar, it flared up brightly. The air beneath the bell jar had once again become "good." Priestley drew an important conclusion: plants improve the air and render it suitable for respiration and combustion. Thus, The Role of green plants was established for the first time. Pursuing his further experiments, Priestley noticed that plants improve the air only in the presence of light. He was the first to suggest the role of light in plant metabolism.

Later, in 1800, the Swiss scientist Jean Senebier provided a scientific explanation of this process, attempting to unravel its physicochemical aspects. By this time, oxygen had been discovered and its properties studied. Senebier established that leaves decompose carbon dioxide and release oxygen under the action of sunlight.

Many scientists, striving to unravel the mystery of the green leaf, made significant contributions to The Study of plant physiology. In the second half of the 19th century, researchers successfully obtained a green alcoholic extract from plants exhibiting a strong Blood-red fluorescence. This substance was named chlorophyll.

A new milestone in the advancement of knowledge regarding photosynthesis was the discovery made by the German naturalist Robert Mayer concerning the plant's absorption of sunlight energy and its conversion into the chemical bond energy of Organic compounds. He was the first to conclude that The amount of carbon deposited in a plant must depend on the intensity of light falling upon it.

A crucial contribution to the study of photosynthesis was made by the Russian scientist K. A. Timiryazev. He investigated the influence of various Regions of the solar spectrum on photosynthesis. He managed to establish that photosynthesis proceeds most efficiently precisely within the red rays, and proved that the intensity of photosynthesis corresponds to the absorption of light by chlorophyll.

K. A. Timiryazev concluded that by assimilating carbon, a plant simultaneously assimilates sunlight, converting its energy into the energy of organic compounds. In his work "The Sun, Life, and Chlorophyll," he detailed and scientifically justified his experiments. K. A. Timiryazev's Laboratory Research Methods and techniques were subsequently employed by other scientists in further studies of photosynthesis.

An act of international recognition of the scientist's achievements was Timiryazev's invitation in 1903 to the Royal Society of London to deliver his famous lecture, "The Cosmic Role of Plants." For his research, he was elected an honorary doctor of several Western European universities.