Historical Discoveries in Photosynthesis

Chloroplasts contain an internal system of membranes called thylakoids. The thylakoids may be arranged in stacks called as grana. The thylakoid membranes not arranged in stacks and are in direct contact with chloroplast stroma are called as stroma lamellae. During photosynthesis, light reaction occurs in grana.
Hill conducted experiments on isolated chloroplasts, having some oxidants like ferricyanide and benzoquinone (Hill reagents). By placing them in sunlight, he noticed evolution of oxygen from water. Hill concluded that if there was hydrogen acceptor in the medium, it would have been reduced. Arnon in 1951, 1954, repeated the experiment with isolated chloroplast and concluded that -
(i) The hydrogen acceptor present in plants is NADP. It is reduced to $NADPH _2$.
(II) An ADP molecule is converted to ATP in light by utilizing inorganic phosphorous. This phenomenon is called as photophosphorylation.

Robert Mayer, 1942, gave a very important concept in which he stated that plants convert light power (light energy) into chemical difference (chemical energy).

Photophosphorylation is synthesis of ATP from ADP in presence of light in the chloroplast. It is also called as photosynthetic phosphorylation. It was discovered by Arnon in 1954. Arnon gave difference between two types of photophosphorylation, cyclic and non-cyclic photophosphorylation. He gave resemblance of photophosphorylation with oxidative phosphorylation. The difference between the two is in photophosphorylation ATP is synthesized using light energy whereas in oxidative phosphorylation, ATP is synthesized using chemical energy. 

Photosynthesis occurs in two stages in a cell. In the first stage, light-dependent reactions capture the energy of light and use it to make the energy-storage and transport molecules ATP and NADPH. The light-independent Calvin cycle uses the energy from short-lived electronically excited carriers to convert carbon dioxide and water into organic compounds that can be used by the organism (and by animals that feed on it). This set of reactions is also called as carbon fixation. The key enzyme of the cycle is called as RuBisCO. The Calvin cycle or reductive pentose phosphate cycle or $C _3$ cycle is a series of biochemical redox reactions that take place in the stroma of chloroplasts in photosynthetic organisms. 

Carbon fixation pathway in C$ _{3}$ plants was discovered by Calvin, Benson and Basham in unicellular alga Chlorella using C-14 labelled carbon dioxide. They fed radiolabelled carbon dioxide to alga and killed algal cells and isolated the organic compounds at various time intervals, through co-chromatography technique in order to decipher the various compounds into which carbon radio label travels.

Photorespiration is the process of uptake of oxygen and production of carbon dioxide in the light by the photosynthesising tissue. It was discovered by Dicker and Tio (1959), when they observed that the rate of respiration of green leaves is much higher in light than in the dark.

Melvin Ellis Calvin was an American chemist most famed for discovering the Calvin cycle along with Andrew Benson and James Bassham, for which he was awarded the 1961 Nobel Prize in Chemistry.

In 1930 C.B Van Niel proved that, sulphur bacteria use $H _{2}S$ and $CO _{2}$ to synthesize carbohydrates as follows:

$6CO _{2}+12H _{2}S\rightarrow C _{6}H _{12}O _{6}+6H _{2}O+12S$

This led Van Niel to the postulation that in green plants, water $(H _{2}O)$ is utilized in place of $H _{2}S$ and $O _{2}$ is evolved in place of sulphur. He indicated that water is electron donor in photosynthesis.

$6CO _{2}+12H _{2}O\rightarrow C _{6}H _{12}O _{6}+6H _{2}O+6O _{2}$

Hatch and Slack pathway is a metabolic pathway for carbon-dioxide translocation occurring in $C _4$ plants. The overall effect of the pathway is to carry $CO _2$ from the mesophyll cells, which are in contact with air, to the bundle-sheath cells, which are the major sites of photosynthesis.

Joseph Priestley conducted experiments in 1774 showing that plants restore the air that has been 'injured' by burning candles or breathing animals, demonstrating the role of plants in gas exchange.

Photosynthesis is a process by which green plants manufacture their food with the help of carbon dioxide and water in the presence of sunlight. It was discovered by Jan Ingenhousz. Through his experiments, he showed that sunlight is essential for the plant process that helps to somehow purify the air fouled by the breathing mouse and the burning candle in Priestley's bell jar experiment. In another experiment with an aquatic plant (Hydrilla), he showed that in bright sunlight, small bubbles were formed around the green parts of the plant while in dark, no bubbles were formed. He identified those bubbles to be of oxygen. Thus, the correct answer is option C.

The Emerson effect is the increase in rate of photosynthesis after exposure to light of wavelength 670 nm far red light and 700 nm, red light respectively. When simultaneously exposed to light of both wavelengths, the rate of photosynthesis is far higher than the sum of red light and far red light photosynthesis rates. The effect was early evidence, that photosystems processing different wavelengths cooperate in photosynthesis. 

Chlorophyll is the liquid substance in a plant cell, which is responsible for its colour. Plants make food when sunlight strikes chlorophyll. Pelletier and Caventou discovered chlorophyll in 1818.

Jan Ingenhousz demonstrated that sunlight is essential to the plant process by showing that aquatic plants produce bubbles in the presence of light but not in the dark.

T. W. Engelmann experimented on Cladophora. Using a prism, he split light into its spectral components and then he illuminated a green alga, Cladophora, placed in a suspension of aerobic bacteria. The bacteria were used to detect the sites of oxygen evolution. He found that the bacteria accumulated mainly in the region of blue and red light of the split spectrum. Thus, action spectrum of photosynthesis was first studied by Engelmann.

Photosynthesis
is a process by which green plants manufacture their food with the help of
carbon dioxide and water in the presence of sunlight. It was discovered by Jan
Ingenhousz. Through his experiments, he showed that sunlight is essential for
the plant process that helps to somehow purify the air fouled by the breathing
mouse and the burning candle in Priestley's bell jar experiment. In another
experiment with an aquatic plant (Hydrilla), he showed that in bright sunlight,
small bubbles were formed around the green parts of the plant while in dark, no
bubbles were formed. Thus, the correct answer is option A.

Theodor Wilhelm Engelmann was a German scientist. In 1883, he performed his famous action spectrum experiment to learn which wavelengths or colour of light were the most effective in carrying out photosynthesis in the green alga.

A) Joseph Priestley first discovered oxygen and discovered that it is released by plants.
B) Jan Ingenhousz proved that sunlight is essential for photosynthesis.

Boussingault was a  French chemist and he made a very significant contribution to the fields of agricultural science and metallurgy.

Melvin Calvin was the professor of chemistry. He was awarded the nobel prize for chemistry for the discovery of various pathways of photosynthesis. 3-phosphoglyceric acid as first $CO _{2}$ fixation product in algal photosynthesis was discovered by Calvin. He used radioactive $^{14}C$ in algal photosynthetic studies. This led to the discovery that the first $CO _{2}$ fixation product was a three-carbon organic acid. He also helped to mark out the complete biosynthetic pathway, hence it is named as Calvin Cycle. The first stable product identified was 3-phosphoglyceric acid (PGA), hence it is named as $C _{3}$ pathway. Calvin cycle occurs in all photosynthetic plants whether they have $C _{3}$ or $C _{4}$ pathway.

Photosynthesis takes place in the green leaves of plants and other green parts of plants like stem etc. The most active photosynthetic tissue in higher plants is the mesophyll of leaves. Mesophyll cells have many chloroplasts, which contain the specialized light absorbing pigments. These pigments are known as photosynthetic pigments. Chlorophyll and carotenoids are the types of photosynthetic pigments. Chlorophyll is the primary pigment and carotenoids are the accessory pigments. Chemistry of photosynthetic pigments was first studied by Willstatter and Stoll in 1912. They discovered that chlorophyll has a tadpole-like configuration. It has a head called porphyrin and a tail made up of long chain alcohol called phytol. Porphyrin head is made up of four pyrrole rings which are linked by methine bridges. 5 atoms— 4 carbon and one nitrogen form the skeleton of each pyrrole ring. Nitrogen lies towards the centre. Thus, the correct answer is option A.

Photosynthesis is a process by which green plants manufacture their food with the help of carbon dioxide and water in the presence of sunlight. It was discovered by Jan Ingenhousz. Through his experiments, he showed that sunlight is essential for the plant process that helps to somehow purify the air fouled by the breathing mouse and the burning candle in Priestley's bell jar experiment. In another experiment with an aquatic plant (Hydrilla), he showed that in bright sunlight, small bubbles were formed around the green parts of the plant while in dark, no bubbles were formed. He identified those bubbles to be of oxygen. Thus, the correct answer is option B.

T.W Engelmann: He described the first action spectrum of photosynthesis. By using a prism he split sunlight into its spectral components (VIBGYOR) and then illuminated green algae Cladophora placed in a suspension of aerobic bacteria. The bacteria were used to detect the sites of O$ _2$ evolution.

A) Stephen Hales is called the father of plant physiology for his extensive research on photosynthesis.
B) Joseph Priestley showed that animals exhale carbon dioxide (impure air) and plants give out oxygen (pure air).
C) Ingenhousz showed that light is essential for photosynthesis.
D) Von Helmont proved that plants require minerals from the soil for photosynthesis.
So the correct answer is 'Priestley'.

• F.F. Blackman, a British plant physiologist discovered that photosynthesis is a two-step process and only one of which uses light directly.
• Hill discovered that green particles obtained from broken cells could produce oxygen from water in the presence of light and a chemical compound, such as ferric oxalate, able to serve as an electron acceptor. This process is known as Hill reaction.
• Benson was the co-researcher of Calvin who discovered the Calvin cycle in photosynthesis.
• The process of photosynthetic photophosphorylation was discovered by Arnon. Photosynthetic photophosphorylation is the process of phosphate group transfer into ADP to synthesize energy-rich ATP molecules making use of light as an external energy source. So, this option is correct.

The first photosynthetic organisms to appear on Earth were likely anaerobic bacteria, which evolved the ability to use light energy before the development of oxygenic photosynthesis in cyanobacteria.

Engelman discovered the action spectrum of photosynthesis in 1833. He found that bacteria accumulated in the region of blue and red light of split spectrum. He thus discovered the effect of the different wavelength of the light on photosynthesis and at that time he discovered the first action spectrum of photosynthesis.
So, the correct option is B.

The process of photophosphorylation was discovered by Arnon. He used the term assimilatory to refer ATP and $NADP$. Photophosphorylation is the process in which light energy is converted into chemical energy through the production of ATP. The process of reduction of $NADP$ into $NADP + H^{+}$ may be denoted as electron transport system (ETS). 

Peter Dennis Mitchell, was a British biochemist who was awarded the 1978 Nobel Prize for Chemistry for his discovery of the chemiosmotic mechanism of ATP synthesis. 

A) Photosynthesis was partially discovered by Jan Baptista van Helmont, a Belgian chemist, physiologist and physician.
B) Stephen Hales proved that plants require light for photosynthesis.
C) Joseph Priestley revealed the essential role of air in the growth of green plants.
So the correct answer is 'Stephen Hales'.

a. Peter Mitchell, in 1961 proposed chemiosmotic hypothesis, according to this hypothesis, the ATP is synthesized by ATPase complexes located on the non-appressed portions of thylakoid membranes, particularly towards margins.

b. Free energy is a concept useful in the thermodynamics of chemical or thermal processes in engineering and science proposed by Gibbs.

c. Daniel L. Arnon in 1961 discovered photophosphorylation, It is the process of phosphate group transfer into ADP to synthesize energy-rich ATP molecule making use of light as an external energy source.

d. CO$ _2$ fixation in dark reaction was thoroughly worked out by M. Calvin.

Hence, the correct answer is 'a-s, b-r, c-q, d-p'.

Julius Robert Mayer made his claim in his The Organic Motion in its Relation to Metabolism which was published in 1845. In this publication, he wrote: "The plants take in one form of power, light and produce another power, chemical difference." He used the term ‘power’ for energy and ‘chemical difference’ for chemical energy. He, therefore, made it clear that plants do not only produce organic matter but also provide the energy which sustains life. Consequently, his finding has made further enlightenment on photosynthesis.

Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants. 

Julius Robert von Mayer was a German physician and physicist. He was the first to state the law of the conservation of energy i.e., energy is neither created nor destroyed. He stated that the sun is the ultimate source of energy for both plants and animals and that when absorbed plants convert this light energy through the process of photosynthesis.

Photosynthesis
is a process by which green plants manufacture their food with the help of
carbon dioxide and water in the presence of sunlight. When light energy is
absorbed by photosynthetic pigment chlorophyll, then it gets exited and photosynthetic
reaction center loses an electron. In this way, light energy is converted to
chemical energy. Conversion of light energy into chemical energy is the primary
event in photosynthesis. R. Mayer stated that in photosynthesis light energy is
converted into chemical energy. He also proposed that the sun is the ultimate
source of energy utilized by living organisms.

Joseph Priestley discovered that plants produce oxygen.
Jean Senebier discovered that the source of this carbon is carbon dioxide. 
Sachs discovered that starch grains are produced in plant leaves and  these are the first visible product of the process of photosynthesis. 
Jan Ingenhousz discovered that light plays a major role in photosynthesis. 

• Most of the experimental work in photosynthesis has been done on Chlorella. Through photosynthesis it multiplies rapidly, requiring only carbon dioxide, water, sunlight and a small number of minerals to reproduce. 
• It is easy to culture and it is easy to understand the photosynthetic process in chlorella cells.
•  Based on the above advantages most of the photosynthetic work was conducted in chlorella compared to hydrilla, spinach leaves, and Chlamydomonas. 

The correcr answer is ' Sachs ' .
Sachs stated that green parts in the plants produces glucose which is later stored as starch and this starch is the first visible product of photosynthesis . in 1865 Sachs proved that chlorophyll was confined to special bodies only , which was later termed as Chloroplasts .

Van Helmont concluded that plants get their food from water. Van Helmont wanted to prove plants use materials from the soil to perform photosynthesis and done an experiment and proved that.