Welcome to kashibiology. In our last post we discussed over all concept about the Transport in Plants under the Plant biology.in this post we’re about to unfold the Historical background about the basis of Life on earth that is Photosynthesis.
Photosynthesis-Basis of Life on Earth
The word photosynthesis is made up of two words one is photo another is synthesis you know that photo stands for light and synthesis means to make something, to produce something.
photosynthesis is going to be a process in which green plants are going to utilize light and they will produce food.
Earlier when we were not aware of the process of photosynthesis.
We didn’t know what food is, but now with lots of technologies, with lots of experiments, and with lots of work we know that food which is being prepared in the process of photosynthesis is carbohydrate.
Should we define photosynthesis, we will definitely say that photosynthesis is a reaction which is occurring in the green parts of the plant or green tissues of the plant.
In which these green parts are going to use sunlight and they will produce carbohydrates.
If you want to chemically represent the reaction you can simply write it down like this.
6 molecules of carbon dioxide are used along with 6 water molecules.
Sunlight is very important and carbohydrates will be produced.
One more important thing is in the process of photosynthesis 6 molecules of Oxygen gas are also released.
This Oxygen gas is considered to be the wasteful product of photosynthesis.
Why it is wasteful because photosynthesis reaction mainly produces carbohydrate and oxygen is the side product.
That means photosynthesis reaction does not occur to produce oxygen but to produce carbohydrate.
Oxygen is simply the side product or oxygen is simply the extra product. That is why it is known as a wasteful product.
But fortunately or unfortunately all the aerobic living organisms on the earth are dependent on this wasteful product of the plants photosynthesis.
If you want to define photosynthesis in more detail or in more technical terms what you can see in this reaction.
On the left hand side you are having carbon dioxide and on the right hand side you are having carbohydrate.
These components have carbon in themselves. Carbon dioxide is also having carbon and carbohydrate is also having carbon.
Do you know what is the difference between the carbon of carbohydrate and carbon which is present in carbon dioxide.
Carbon dioxide carbon is actually inorganic carbon and the carbon which is present in carbohydrate is organic carbon.
So how you can define photosynthesis- is the conversion of inorganic carbon into organic carbon by using sunlight as an energy source.
In another way you can see that light is being utilized in the reaction and carbohydrate is being produced.
Someone asks you what is light and what should be the reply regarding the light. Light is the visible part of electromagnetic radiation.
Light is a form of energy. It is a form of radiation energy. Light is made up of photons and photons have energy themselves.
The light is a form of energy and this carbohydrate which is a type of chemical when being utilized in glycolysis and TCA cycle it will also produce energy.
indirectly we can also say that carbohydrates are also the form of energy because carbohydrates are having energy rich bonds. So carbohydrates are also a form of energy.
Therefore the definition of photosynthesis is conversion of inorganic carbon into carbohydrate.
Conversion of light energy into chemical energy is also known as photosynthesis.
So finally photosynthesis is the process by which plants are using light energy to convert inorganic carbon into organic carbon of carbohydrate.
This is the simplest and cleanest definition of photosynthesis reaction.
Historical Aspects of Photosynthesis
We are sharing some important contributions of very famous scientists in Discovery of different steps of photosynthesis. We know that photosynthesis is not a single step process.
Ideally if we want to learn photosynthesis in detail, then there is a lot of literature data we need to understand.
I want to mention some experiments, discoveries and the contribution of scientists which related to the Photosynthesis from the year 1727 to 2000.
We have to try to give you a brief discussion about the historical data about the discoveries and contribution of different biologists in years wise, but if any mistakes or updates are needed please comment us.
Year-1727:
It was Stephen Hales who recognized the importance of sunlight air and green Leaves or green tissues for nourishment of plants.
Year-1770:
Joseph Priestley confirmed that oxygen evolved in the process of photosynthesis by a simple but famous experiment popularly known as Bell jar experiment in 1774 Joseph Priestley discovered oxygen.
Year-1779:
Jan Ingenhousz worked out on an aquatic plant and confirmed that in bright light small bubbles (oxygen) were formed which purified the air.
Year-1783:
According to Lavoiser the pure is Oxygen while the Foul air is carbon dioxide.
Year-1804:
De. Saussure showed that water is essential in photosynthesis and also carbon dioxide used by plants with the releasing of oxygen.
Year-1818:
Pelletier and Caventon discovered and named photosynthetic pigment chlorophyll.
Year-1845:
Von Mayer-according to him green plants have the ability to change solar energy into chemical energy in the process of photosynthesis.
Year-1854:
Sachs- confirmed that,it is starch, a type of complex polysaccharide which is the visible and stored product of plant form from the glucose after photosynthesis.
Year-1864:
G.G.Stokes- was able to separate for the first time a pure fraction of chlorophyll a and chlorophyll b.
Year-1888:
Engelmann, by his experiments, gave an action spectrum of photosynthesis. He found that the red and blue spectrum of light is very effective in photosynthesis.
Year-1905:
Blackmann proposes limiting factors and also dark phases of photosynthesis.
Year-1912:
Wilstatter, Still & Fischer- first study about the structure of chlorophyll.
Year-1920:
Otto Warburg- study the effect of high intensity of light, high oxygen concentration and effect of cyanide poison on the process of photosynthesis.
Year-1925:
Kellin- give the term cytochrome.
Year-1931:
Van Neil-by his experiment on green and purple sulphur bacteria demonstrated that in the photosynthesis carbon dioxide reduction takes place into carbohydrate while oxidation of water as well as also reported that photosynthesis is light dependent process.
Van Neil experiments clearly differentiated two types of photosynthesis, namely oxygenic and non oxygenic. because green sulphur bacteria in his experiment used hydrogen sulphide gas Instead of water as hydrogen donor.
Hence there is no oxygen evolved in the experiment, rather than sulphur gas evolved. Therefore he confirmed that oxygen evolved in photosynthesis from the breaking of water, not from the carbon dioxide.
Year-1932:
Arnold and Emerson work-used different temperature and light flashes they found out the existence of dark and light phases of photosynthesis.
Year-1937:
Hill-by his experiment he stated that oxygen released during light reaction not in dark reaction.
Year-1940:
Ranson and Thomas- gave the term CAM and observed it in succulent plants (belongs to Crassulaceae family).
Year-1941:
Hassid, Kamen and Rumen-day workout heavy isotopes of oxygen 18 and found that oxygen evolved in photosynthesis comes from splitting of water not from carbon dioxide.
Year-1954:
Arnon et al-discovered the phosphorylation reaction of photosynthesis and also worked on carbon dioxide fixation.
Year-1954-1955:
Melvin Calvin discovered and identified the pathway of carbon dioxide fixation during dark reaction and called it C3 cycle.
Year-1957:
Emerson- discovered red and far Red light effect on photosynthesis later it is called immersion enhancement effect.
Year-1959:
Dicker and Tio-discovered photo respiratory process in tobacco plant.
Year-1960:
Hill and Bendall- Proposed there are two photo systems.
Photosystem I and Photosystem II work together in non-cycled photophosphorylation and are called the ‘Z’ scheme of photophosphorylation in light reaction.
Year-1961:
Menke-called thylakoid is a structural and functional unit of chloroplast.
Year-1961:
Peter Mitchell-proposed his famous theory popularly known as Chemiosmotic theory in which he explained exactly how ATP formation takes place in mitochondria and chloroplast.
Year-1963:
Biggins and Park- Quantasome is a piece of thylakoid membrane.
Year-1965:
Hatch and Slack- discovered another pathway of carbon dioxide fixation in some plant and called its C4 pathway.
Year-1996:
Kozaki and Takeba explained how photorespiration protects the plant from photo oxidation.
Year-2000:
Reinfelder- explain that confirms that items also perform C4 pathway of carbon dioxide fixation.
Bessel Kok- discovered Photosystem I (P-700).
Reinfelder- discovered Photosystem II (P-680).
Some Famous Experiment
Sachs work-
Sachs in 1864 for the first time said that the end product of photosynthesis is carbohydrate.
Today with lots of technology and knowledge we know what the end product of photosynthesis is glucose.
But at an earlier time when we did not have any technology and so much knowledge regarding living organisms.
Sachs for the first time said that carbohydrate is being produced in photosynthesis reactions.
Before this we were Not aware of the end product of photosynthesis.
Priestley work-
After this there was a scientist whose name is Priestley.
Priestley for the first time performed an experiment which is famously known as the Candle jar experiment.
What is this candle jar experiment?
In this experiment, Priestley designed two setup.
He took a burning candle, and he put a large glass jar on the candle.
After sometime he observed that the candle is turned off now the candle is no more lightning.
In the second setup he put a mint plant along with the burning candle. The same setup was there but this time he also so I took a mint plant.
Inside the Jar he observed that this time the candle was burning for a much longer time than the previous one.
So he concluded that definitely this mint plant is producing some kind of gas which is keeping the candle burning and later on it was discovered that it is the Oxygen gas.
which is responsible for the continuous burning of candles. Priestley was credited with the discovery of Oxygen gas.
Priestley was the first person who proved that in photosynthesis reaction Oxygen gas is produced and Sachs was the person who said that carbohydrate is produced.
De. Saussure Hypothesis-
We know that on one side of the reaction there is carbon dioxide and water molecules and at the right hand side of the reaction carbohydrate and Oxygen gas.
Now the big question is from where this Oxygen gas is coming because both the reactants at the left hand side are having oxygen in themselves.
Carbon dioxide is also having the oxygen and water molecules are also having the oxygen.
There was a scientist whose name is the saucer and the Saussure first predicted that it is the carbon dioxide. which is going to give rise to oxygen but his thinking was absolutely wrong.
it is not the carbon dioxide which is going to produce oxygen but it is the water molecule which is going to give rise to Oxygen gas produced in photosynthesis reaction.
How does it happen? It is very simple. There were two scientists namely Ruben and Kamen. What did they do?
Ruben & Kamen work-
They used a carbon dioxide gas which has Oxygen 18 isotope. Why did they use Oxygen heavy isotopes? Oxygen 18 isotope is a heavy isotope, hence it is easily detected. but they gave normal water (normal Oxygen in water) to the first plant.
So in the first set up or in the first plant water is quite normal. it has normal oxygen. Carbon dioxide which is being utilised is having a heavy isotope of oxygen.
in the second plant they reverse the method that means the carbon dioxide is quite normal but this time the water they used is having Oxygen 18 isotope. Heavy isotopes of oxygen plants are going to release oxygen.
that is the fact but if in real sense oxygen is coming from carbon dioxide. In the first plant it should be oxygen 18 or if the oxygen is coming from water then in the second experiment it should be oxygenating.
and later confirmed that, in the second experiment the released oxygen is not the normal one, but the heavy isotope of oxygen that means oxygen 18.
Ruben and Kamen confirmed that oxygen is released from water in photosynthesis, and today we know very well that there is a process known as photolysis of water or photo oxidation of water. In which oxygen is produced from water molecules.
Engelmann work-
It was quite confirmed that the sun is a source of sunlight for green plants. all kinds of light used in photosynthesis by the plant.
Whatever light is reaching up to the Earth’s surface is not being utilised by a photosynthesis scientist whose name is Engelmann.
Engelmann performed an experiment and he proved that out of different types of light.
it is the visible light in which plants can do photosynthesis
For this he took two plants.
When he provided the first plant with Gamma radiation or X radiation or ultraviolet radiation or microwaves or radio waves he came to know that this plant died out, but didn’t photosynthesize.
He provided the second plant with visible light. He came to know that this plant survived and also did photosynthesis.
Hence it is proved that in photosynthesis only visible light is required.
visible light is the mixture of seven different types of lights as we know there is a visible spectrum in which 7 different types of lights are present.
Violet light, Indigo light, blue light, yellow light, Orange light and red light. so visible light itself is made up of seven different types of light. Violet light starts from 400 to 700 nm.
There is one more question: can plants do the same level of photosynthesis in all types of light? if you are going to provide a plant with only violet light and you are going to plant with only red light that means monochromatic light can both the plants produce the same level of carbohydrate, the answer is no.
because when we took a plant and gave it violet light and we took a plant and gave it only red light.
we found that photosynthesis and carbon carbohydrate production is much higher in, red light provided plant
In which maximum carbohydrate was produced so that’s how we can simply conclude that out of 7 different types of lights which are used in photosynthesis.
It is the red light in which plants do maximum photosynthesis.
that in red light plants perform maximum photosynthesis but how we can see that from the sun not a particular type of light is coming on the earth surface.
Light is like a run of photons. It is simply the shower of photons and many photons are coming together in this shower or in this range of photons there are different types of photons.
Some Basic Points about Phases of Photosynthesis-
The photosynthesis reaction is completely divided into two reactions. one is known as light reaction another is known as dark reaction.
The light reaction cyclic electron flow by which energy rich chemicals form such as ATP and any NADPH.
These chemicals are used in the reduction of carbon dioxide into carbohydrates.
So we can say it is the assimilation of carbon dioxide but for this kind of assimilation the energy produced in light reaction is utilised in dark reaction to reduce carbon dioxide to make Glucose.
So the products of light reaction are used in dark reactions and the carbohydrate is produced and the carbohydrate is utilised by plants and other animals.
The site of light reaction are grana or thylakoids and dark reaction is in stroma of chloroplast.
a light reaction occurs in two manner whether it is non cyclic electron flow or it is cyclic electron flow.
In stroma either it is C3 cycle or C4 cycle or cam cycle these are the types of dark reactions.
Note-we shall discuss details in coming post
Conclusion-
Hope after reading this post you will be able to understand how the different stages of photosynthesis has discovered by various experiments.
Thanks for reading this post.
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