experiment von engelmann

Contribution to the History of Photosynthesis: Theodor Wilhelm Engelmann and Hugo Von Mohl

Théodor Wilhelm Engelmann  (1843 -1909) was a German botanist and physiologist.

He also shed important enlightenment on the functions of light in photosynthesis, particularly  light quality .

It is now a well accepted fact that the process of photosynthesis is affected by the  properties of light  which include light quality, light intensity, and light duration.

Von Mohl also recognized the presence of  starch  in the chloroplasts and developed the concept that this starch is a reserve food (Spoehr 1926).

He then illuminated the alga with different colors of light using a prism.

It has long been established that some forms of algae constitute the nano-plankton.

Note:  The lists of contributors and Literature Cited are in the  History of Photosynthesis  Mainpage.

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• Biology Article
• Photosynthesis Early Experiments

Early Experiments on Photosynthesis

Table of contents, introduction, photosynthesis discovery – early experiments, experiment to prove carbon dioxide is essential for photosynthesis, other experiments.

Photosynthesis is a light-dependant process that plants use to produce their own food. It is the process by which plants convert light energy into chemical energy, which can be used later for plants’ own processes. During this process, oxygen is produced as a byproduct. Photosynthesis was discovered only in 1800. To prove the existence of photosynthesis in plants, many scientists performed numerous experiments.

Let us have a detailed look at the early experiments on photosynthesis.

Also Read:  What is Photosynthesis

Since photosynthesis is a light-dependant process, it only takes place in the presence of sunlight. But along with sunlight, the plant also requires water and carbon dioxide as raw materials for this process to synthesise carbohydrates. Green plants also possess a green pigment known as chlorophyll which helps in capturing light energy. All these key features of photosynthesis were revealed later during the mid-nineteenth century when numerous scientific studies were conducted on photosynthesis.

Below mentioned are the experiments that were conducted by the early scientists in support of photosynthesis.

Materials required: A healthy potted plant, a wide-mouthed glass bottle with a split cork, potassium hydroxide solution (KOH), and starch solution.

Experiment:

• Select a healthy potted plant and place it in the darkroom for two to three days to ensure the leaves are free from starch.
• In a wide-mouthed glass bottle, add 10-15 ml of potassium hydroxide solution and split the cork vertically.
• Now carefully insert half part of a leaf into a glass bottle through the split cork and the other half exposed to air.
• Place the complete unit undisturbed in sunlight for about 3 – 4 hours.
• After 4 hours, detach the leaf from the plant and slowly remove it from the bottle and test it with the starch solution.
• We can observe that the half part leaf which was inside the glass bottle (KOH solution) did not show any colour change, but the other half part exposed to the surroundings turned its colour to dark brown, indicating the presence of starch in it.

Conclusion: In this experiment, we can conclude that carbon dioxide is essential for photosynthesis. Both the portion of the leaf received the same amount of water, chloroplasts , and sunlight but the half part which was inside the glass bottle did not receive carbon dioxide.

After discovering the importance of carbon dioxide in photosynthesis, many experiments were conducted to understand other essential factors for this process. Joseph Priestly was one of the first scientists to perform these experiments.

Experiment by Joseph Priestley

In 1770, after a series of experiments, Joseph Priestley came to a conclusion regarding the essentiality of air for photosynthesis and also for the growth of plants.

Materials required: A bell jar, candle, rat, and a plant.

• Priestley kept a burning candle and a rat together in the single bell jar.
• After some time, the candle was extinguished, and the rat died.
• For the second time, he kept a burning candle, a rat, and a green plant together in the bell jar.
• He observed that neither the candle got extinguished nor did the rat die.

Conclusion: Based on his observations, Priestley concluded that in the first case, the air in the bell jar got polluted by the candle and rat. However, in the second case, the plant reinstated the air that was spoiled by the candle and the rat.

But it took another few years to reveal what was exactly released by the plant to keep the rat alive and the candle burning.

Jan Ingenhousz: He proved that sunlight is essential for the photosynthesis process during which carbon dioxide is used and oxygen is produced.

Jean Senebier: He demonstrated that during photosynthesis, carbon dioxide in the air is absorbed, and oxygen is released by the plant.

Julius Robert Mayer: Mayer proposed the idea that light energy is being converted into chemical energy during photosynthesis.

Julius Von Sachs: He discovered that the photosynthesis process leads to the production of glucose molecules.

T.W.Engelmann: Engelmann was the scientist who discovered the importance of chlorophyll in photosynthesis.

Cornelius van Niel: He introduced the chemical equation of the photosynthesis process when he revealed that the oxygen released by plants at the end of photosynthesis comes from water and not from carbon dioxide.

Also Read:  Photosynthesis in Higher Plants

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Are any experiments that had been done but related to other factors which affecting the rate of photosynthesis?, If so then I would be grateful if you can send me any of them. I am very interested to do such experiment and that will be also a part of my assessment task that I will be doing next week. Most of the information that I get from the source really help me, and I hope that it is vital for me.

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Highlighting Theodor W. Engelmann's “Farbe und Assimilation” [Color and Assimilation]

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Some pioneers of photosynthesis

1. plants need water.

2. Plants produce oxygen

A few years later, in 1777, Antoine Laurent de Lavoisier (1743-1794), French chemist, philosopher and economist (Figure 2), replaced the theory of phlogistics with the “general  théorie of combustion ”. It gives the name of oxygen to the gas involved.

3. Plants, oxygen and light

(1) Light is necessary for the plant to restore air (photosynthesis);

(2) only the green parts of the plant are involved in this restoration;

(3) all living parts of the plant “damage” the air, but the extent of air restoration by a green plant far exceeds its harmful effect.

A century later, Theodor Wilhelm Engelmann (1843-1909), a German physiologist (Figure 3), demonstrated the role of the colour of light in an experiment with filamentous algae (spirogynous type) illuminated with coloured spots, then with a prism, in which aerobic bacteria* serve as an indicator of oxygen production. Bacteria density was highest in the areas illuminated by the blue and red lights.

4. Plants use carbon dioxide

Jean Senebier (1742-1809), a Swiss naturalist, meteorologist and pastor (Figure 4), studied gas exchanges between plants and the atmosphere. He showed that plants absorb carbon dioxide and produce oxygen in the presence of light and published a book in 1783 entitled “ Research on the influence of sunlight in transforming fixed air into clean air by vegetation” . These observations are reinforced by those of Nicolas-Théodore de Saussure (1767-1845), a Swiss chemist, biochemist and botanist (Figure 5): de Saussure shows that plants need carbon dioxide, but also water, nitrogen compounds and mineral salts to ensure their nutrition and growth.

Jean-Baptiste Joseph Dieudonné Boussingault (1802-1887), French chemist, botanist and agronomist, is considered the founder of modern agricultural chemistry (Figure 4). After developing air analysis techniques, he demonstrated – around 1860 – that the volume of gaseous oxygen released and the volume of CO2 absorbed are almost identical.

5. Chlorophyll and chloroplasts

Hugo von Mohl (1805-1872), a German botanist (Figure 6), gave the first detailed description of “Chlorophyllkörnern” (chlorophyll granules) in green leaves in 1837.

Arthur Meyer (1850-1922), a German botanist, cell biologist and pharmacognosist (Figure 6), was the first to name and describe chlorophyll-containing structures in chloroplasts (which Meyer called “autoplasts”) known as grana.

6. Plants transform light energy: photosynthesis

Julius von Sachs (1832-1897), a German botanist (Figure 7), participated very actively in the development of plant physiology. In particular, it demonstrates that starch grains present in chloroplasts are formed under the influence of light.

It was finally in 1930 that Cornelis Bernardus van Niel (1897-1985), a Dutch-American microbiologist (Figure 8), demonstrated that photosynthesis is a light-dependent redox reaction, in which the hydrogen of an oxidizable compound (H 2 A) reduces carbon dioxide to cellular material (CH 2 O)x. This reaction is expressed according to the equation:

CO 2 + H 2 A + light → (CH 2 O)x + A 2 + H 2 O

Notes and References

Cover image. Joseph Priestley [Source: Ozias Humphrey (1742-1810) / Public domain]

[1] Lavoisier, very interested in Van Helmont’s work, points out that the word gas comes from the Dutch word ghoast which means spirit. He adds that the English “express the same idea by the word ghost and the Germans by the word geist”.

[2] Phlogistic theory is a chemical theory that explained combustion by postulating the existence of a “flame element” present within combustible bodies.

[3] Gest H. (2002) History of the word photosynthesis and evolution of its definition. Photosynth Res 73(1-3):7-10.

• Pol D. (2007) History of Plant Biology, History of Knowledge of Plant Physiology. Fondation La main à la pâte : https://www.fondation-lamap.org/fr/page/11407/histoire-des-connaissances-sur-la-physiologie-des-plantes
• Website “Photosynthesis education”. https://photosynthesiseducation.com/discovery-of-photosynthesis/

• Kompaktlexikon der Biologie

Engelmann-Versuch

Kompaktlexikon der Biologie : Engelmann-Versuch

Engelmann-Versuch , das nach T.W. Engelmann (1843-1909) benannte Experiment zum Nachweis des Aktionsspektrums der Fotosynthese . Engelmann nutzte ein Prisma, um das Sonnenlicht in verschiedene Spektralbereiche aufzutrennen und damit die fädige Grünalge Spirogyra zu bestrahlen. Bestimmte Zellen wurden so durch blaues, andere durch grünes und wieder andere durch rotes Licht bestrahlt ( vgl. Abb. ). Der während der Fotosynthese entstehende Sauerstoff diente Engelmann als Maß für die fotosynthetisch wirksamen Wellenlängen des Lichts. Um die Sauerstoffbildung verfolgen zu können, setzte Engelmann aerotaktische Bakterien zu ( Aerotaxis ), die sich vor allem im blauen und roten Bereich des Spektrums ansammelten, wohingegen sie bei grün bestrahlten Algenzellen kaum vorhanden waren ( Grünlücke ).

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Engelmann’scher Bakterienversuch

Engelmann versuchte zu zeigen, dass Photosynthese und Sauerstoffproduktion abhängig von der Wellenlänge des Lichts sind. Für seinen Versuch spaltete er Licht mit einem Prisma in seine einzelnen Farbbestandteile auf. Als nächstes leuchtete er eine Faden-Grünalge mit den einzelnen Lichtfarben an. Um die Photosyntheserate zu messen, gab er aerotaktische Bakterien hinzu, die sich dorthin bewegten, wo Sauerstoff war. Er konnte feststellen, dass die Bakteriendichte im roten und blauen Licht am größten war, bei diesen Wellenlängen musste die Photosyntheserate also am höchsten sein. Weiters konnte er feststellen, dass die Photosynthese in Chloroplasten stattfindet: Das Anleuchten der Chloroplasten lockte Bakterien an, während sie beim Anleuchten anderer Zellbestandteile ausblieben.

Erklärung für Kinder:

Herr Engelmann hat herausgefunden, dass die Photosynthese abhängig von der Wellenlänge des Lichts ist. Die Pflanzen mögen nämlich nicht jedes Licht, sondern nur z. B. blaues oder rotes. Für seinen Versuch leuchtete er eine Alge mit verschiedenen Farben an. Um die Photosyntheserate zu messen, benutzte er ganz besondere Bakterien, die dorthin wandern, wo die Luft am saubersten ist. Schnell konnte er sehen, dass im roten und blauen Licht die meisten Bakterien waren. Dort musste also die Luft am saubersten sein und somit die Photosyntheserate ganz hoch.

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Pictorial Demonstrations of Photosynthesis

• Published: April 2004
• Volume 80 , pages 421–425, ( 2004 )

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• Roger P. Hangarter 1 &
• Howard Gest 1  

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Theodor Engelmann's experiments in 1882 provided the first recorded visual demonstration of light wavelengths that are absorbed by photosynthetic pigments. Later, starch images in intact leaves were used to demonstrate photosynthesis in green plants. Similarly, light-induced chloroplast movements can form images in leaves as a result of changes in light transmittance through leaves and photoinhibition can form images that can be visualized by whole leaf chlorophyll fluorescence. This paper provides a brief account of how photosynthesis has been used to create an assortment of 'living images' that offer stunning demonstrations of various aspects of photosynthesis.

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Hangarter, R.P., Gest, H. Pictorial Demonstrations of Photosynthesis. Photosynthesis Research 80 , 421–425 (2004). https://doi.org/10.1023/B:PRES.0000030426.98007.6a

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What did Jan Ingenhousz discover about photosynthesis?

Dutch-born British physician and scientist Jan Ingenhousz discovered that light is necessary for photosynthesis . This observation built upon work begun by English scientist Joseph Priestley , who had burned a candle in a closed container until the air within the container could no longer support combustion. Priestley then placed a sprig of mint plant in the container and discovered that after several days the mint had produced some substance (later recognized as oxygen) that enabled the confined air to again support combustion. Ingenhousz followed up on this work by placing plants in a transparent container and submerging them in water. He noticed that, following exposure to sunlight, little bubbles appeared on the undersides of the plants’ leaves. Bubbles eventually stopped being produced, however, when the plants were placed in the dark.

A second key observation made by Ingenhousz was that the bubbles produced by plants upon light exposure appeared only on the plants’ green parts. Thus, he concluded that only the green parts had the ability to restore the combustible substance (oxygen) to the air.

Ingenhousz further observed that all living parts of the plant “damage” the air (respire), but the extent of air restoration by a green plant far exceeds its damaging effect. In other words, in darkness he found that plants release carbon dioxide gas, the substance responsible for “damaging” the air. However, plants make up for this by producing oxygen at a rate that is far greater than the rate at which they release carbon dioxide.

Engelmannscher Bakterienversuch

• Photosynthese

Der Engelmannsche Bakterienversuch (nach Theodor Wilhelm Engelmann) dient dazu, die lichtabhängige Sauerstoffbildung bei der oxygenen Photosynthese in verschiedenen Bereichen des Lichtspektrums grob zu quantifizieren.

Zu diesem Zwecke lenkte Engelmann einen Lichtstrahl durch ein Prisma und projizierte das entstehende Lichtspektrum auf einen dünnen Algenfaden, der sich in einem wässrigen Medium befand, das Bakterien enthielt, die positiv chemotaktisch auf Sauerstoff reagieren. Je nach Farbe des Lichts, das auf den Algenfaden traf (vom langwelligen Rot über Orange, Gelb, Grün und Blau bis zum kurzwelligen Violett), produzierte das in den Chloroplasten enthaltene Photosynthesesystem mehr oder weniger Sauerstoff, worauf sich die Bakterien mehr oder weniger stark an den betreffenden Stellen ansammelten. Die Menge der angesammelten Bakterien nahm er als ungefähres Maß für die Photosyntheserate, die der Sauerstoffproduktionsrate entspricht.

Das Resultat zeigt deutlich, dass die Optimalbereiche für die Photosynthese im langwelligen Rot und im kurzwelligen Blau liegen, dazwischen im Bereich von Grün und Gelb ist die Photosyntheserate geringer. Dies geht ungefähr parallel mit den Absorptionsmaxima der Photosynthesepigmente (siehe Grafik).

Mit den Absorptionsmaxima der Photosynthesepigmente kann auch die grüne Farbe der Pflanzen erklärt werden: Während das rote und das blaue Licht fast vollständig absorbiert werden, werden das grüne und gelbe remittiert oder durchgelassen.

• Elmar Weiler, Lutz Nover; Begründet von Wilhelm Nultsch: Allgemeine und molekulare Botanik . Thieme, Stuttgart 2008 , ISBN 978-3131476616.
• Engelmannscher Bakterienversuch (Animation): http://www.youtube.com/watch?v=Vy7bCCu65dk