Photosynthesis is the process by which green cells convert light energy into chemical energy, synthesizing glucose from carbon dioxide and water through two phases: the light-dependent reactions (occurring in thylakoid membranes) that produce ATP and NADPH2, and the light-independent Calvin cycle (occurring in stroma) that uses these products to fix carbon dioxide into glucose. The process involves photosystems (PSI and PSII), accessory pigments (chlorophylls, carotenoids, xanthophylls), and specialized structures like grana and stroma lamellae. C3 plants use the Calvin cycle directly in mesophyll cells, while C4 plants (like sugarcane and maize) have Kranz anatomy with bundle sheath cells that concentrate CO2 to prevent photorespiration. The rate of photosynthesis is controlled by limiting factors such as light intensity, CO2 concentration, and temperature, as described by Blackman's Law of Limiting Factors.
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Hello children, I'm Ravi Chandra from Sri Chaitana, an organization committed in students dreams of achieving something big. And stay with me for an hour. I'll take you to a tour of a chapter called photosynthesis.
And I promise you, you'll be extremely happy after listening to it. Don't leave me. All right. So we are going to start this chapter photosynthesis and we'll run through this topic very fast. First I start with the definition of photosynthesis. It is the synthesis of organic compounds. What is that organic compound? Glucose from water and CO2 from simple inorganic compounds.
Next important point which time it take place. Light phase occur during daytime.
Even the dark phase also occur during daytime. This is something which you know you study in your lower classes.
What are the cells in which photosynthesis occur? Green cells. This is simple point. What type of conversion? It's a energy transduction process. Light energy is converted to chemical energy. First ATP in light phase. Then this is used in the synthesis of glucose. Now what is this process? This process is anabolic process constructive.
And what is the cell organally involved in this process? It is chloroplast.
Chromataphors are seen in blue green alga. They are the extensions of plasma membrane which contain pigments. Right?
Then next one is the equation for photosynthesis.
6 CO2 + 12 H2O give rise to glucose, oxygen and water. Look here water is donating its hydrogens to carbon dioxide.
So it means that water is losing hydrogens's therefore it's getting oxidized. Carbon dioxide is gaining hydrogens therefore it's getting reduced. So the compound which gets oxidized is water therefore it's a reducing agent and the compound which get reduced is carbon dioxide. Having said that in some green sulfur bacteria it is not water it is hydrogen sulfide which is actually getting oxidized. That is the reason you know pretty well it is an oxygenic photosynthesis.
Then the most important one from where this compounds now look at this this is simple carbon in glucose should from carbon dioxide.
Hydrogen in glucose should come from water. Oxygen in glucose come from carbon dioxide.
Oxygen liberated come from water. And hydrogen here should come from water.
And oxygen here will come from carbon dioxide. Well, these lines are looking little difficult for you to understand, isn't it? I shall I make it easy. 12 oxygen atoms are there. Six 2 are 12. It means that all the oxygen liberated is coming from water, isn't it? Then the oxygen present here and the oxygen present here should definitely come from carbon dioxide. That's it. Same thing I've written here. What did I write here? Carbon in glucose come from carbon dioxide. Hydrogen in glucose come from water. Oxygen in glucose come from carbon dioxide. Oxygen released is from water. And the scientist name you remember Neil. Hydrogen in product water come from substrate water. Oxygen in product water come from carbon dioxide.
Nice. We made a good start. Right. Where is photosynthesis observed? It is observed in monerins, protestants and plants. And what is about monorins? It shows both oxygenic and an oxygenic.
Oxygenic in blue green alga whereas in green sulfa and purple green sulfur it is an oxygenic. That's what I written.
Photosynthesis is oxygenic in monerance that is blue green alga is an example for that protestants and plants.
Photosynthesis is an oxygenic because sulfur compounds is going to get oxidized. That is the reason it is an oxygenic.
This word is little tricky. Cheo autotroof. The general belief of most of you is autotroof means it should perform photosynthesis. But the fact of the matter is even though they are autoro that doesn't perform photosynthesis.
They oxidize the inorganic chemicals present in them and thereby gain energy.
So therefore they are not examples of photosynthetic organisms even though they are auto drops. Next one, photosynthesis is a physicochemical process. Why we say that? There are some physical processes and chemical processes involved in this. What are the physical changes? Here I've written absorption of light is physical.
Excitation of electron from chlorophyll is physical. Photosis of water is physical. Whereas synthesis of ATP and NADPH2, synthesis of sugar from glucose, these are the ones which are chemical.
That is the reason your textbook says it's a physicochemical process.
Photosynthesis is an ultimate source of food naturally because it is going to synthesize glucose which is the starter produces and thereby the entire food chain depends on it and photosynthesis not only release oxygen during light phase it also produce glucose during dark phase. These are the two vital compounds which are produced. That completes the introduction part to photosynthesis children. Now we get into some experiments which are there in your textbook. The first is variegated leaf.
Look at this. A leaf has got both green and non-green parts. Only green parts respond to iodine test. Star starch iodine test. Non-green parts doesn't. So it means that it explains the role of chlorophyll in photosynthesis that is variegated. Then black paper leaf experiment. Let us not waste our time here. A part of the leaf is covered with a black paper. The remaining part of leaf was normal. That part of the leaf which is not covered with black paper respond to iodine test. Not the one which cover with black paper. So therefore this experiment explains the role of light in photosynthesis. Then Maul's half leaf experiment. Half of the leaf is exposed to Koh and you know children KO absorbs all the CO2. So therefore this part of the leaf doesn't get CO2. So therefore there is no starch. The other part will get CO2.
There is starch. So therefore the role of carbon dioxide in photosynthesis is explained by Maul's halfleaf experiment.
Now the next important one is the scientist names. The first in that list is Priestly. Let me show you a nice diagram based on that we'll be discussing on it. Look at this. In the first bell jar, you observe the candle is burning and the rat is happy. Isn't it? Yes. But after some time, the candle was put off and the rat died. You may ask me why such sad things happened.
Simply because there is no oxygen. The deficiency of oxygen is the reason why the rat got suffocated and the candle was put off. Then you know what Priestley did? He thought that he should not kill rat. So therefore what he kept?
He kept a mint plant under the bell jar.
Now mint plant is able to perform photosynthesis and you know children in photosynthesis CO2 is actually taken in and oxygen is liberated. So the burning candle and mouse was respiring and liberating CO2 and the plant is taking the CO2 and by a process called photosynthesis evolved oxygen and that oxygen kept the candle burning and made and keep and kept the mouse happy or alive. So that is the most important point. And what Presley said here what I have written here experiment one candle and mouse in bell jar the candle did not burn and the mouse died both candle and mouse damage the air all right by taking up all the oxygen. Then what the next one experiment two here the candle mouse and mint plant. All right. What did you observe? The candle continued to burn in closed space and the mouse was alive.
The plants restore the quality of the air. What did Presley said? Presley said plants take bad air that is CO2 and liberate good air that is oxygen. That's very simple. And there is one word. Is there any way where we can lit the candle without opening the bell jar? All right. There are many ways where we can lit the candle without the opening the bell jar. Using the burning glass or or magnifying glass better way of saying using a mirror all right to direct light into the jar are some of the ways to relight the candle. This is a question which was asked. Then engine house you know what did he do? He did the priestly experiment. He kept the bell jar the entire setup during daytime because light was there. The plant was able to perform photosynthesis and evolve oxygen keeping the mint plant keeping the mouse alive. In the same setup when it kept in dark you know what happened there is no photosynthesis. There is no evolution of oxygen and the entire mouse and candle was put off. Not only that children priestly sorry engine house did one more experiment oxygen bubbles was seen from a plant called hydrillaa the name is not there in your book hydrilla and this oxygen bubbles evolved only during daytime because light phase and dark phase occur only during daytime in the night time there was no oxygen bubbles from hydrillaa so again what is the ultimate summary of engine house experiment light is essential for photosynthesis That's a very important point.
Sachs plants produce starch or glucose.
All right. In green substances in plants are located in special bodies called chloroplast. And you know what is that green substance? The green substance is chlorophyll. Then we talk about angle man. Just like Spider-Man, He-Man, Engleman is associated with action. Now what did he do? He took a light prism to break light an alga called cladophora and an aerobic bacteria. Let me show you the diagram. What happened here? Based on that we'll go through this. Look here. What did the prism do? Divided the light into seven colors. He exposed cladophora to all the seven colors. That wavelength at which the rate of photosynthesis is more is blue and red.
Naturally oxygen is evolved as a product in light phase. You know pretty well because of oxygen evolution in large quantities in blue and red more aerobic bacteria accumulated in that suspension.
Clearly signifying that blue light and red light are the most effective light in photosynthesis. And be careful children angle man is associated with action spectrum not absorption spectrum.
And what is an alga used by him?
Cladophora. What is an alga used by Calvin in his experiments? Chlorella. So they bec for these two examples are important. Alga used by Engleman is cladophora by Calvin is chlorella. And we talk about warneal. This is simple experiment. All of you know that. All right. We already discussed that if it is water. All right. Then the oxygen is evolved.
And if it is not water, if it is H2S, oxygen is not evolved. Look at this two.
Look at these two. Carbon dioxide is common in both. Only when water is there, oxygen is evolved. When water is not there, H2S is there. There is no evolution. That was a time where the people was little confused about this oxygen release. Is it coming from CO2 or water? Because both of them contain oxygen. War Neil conveniently with his experiment working on green sulfur bacteria proved to the world that oxygen evolve come from water not from carbon dioxide. This is a very important point.
Reuben and Carmon um not that much important children. If you look at what did he do? He has taken 06 here. He took 08 here.
So naturally this will be 016. This will be O6 and this will be O8.
So it's very clear that oxygen is coming from water. Therefore it is 08. Oxygen in glucose and the product water is coming from carbon dioxide. Therefore it is 016. And by the way let me put one question. What are the two isotopes used in photosynthesis? In light phase it is 08 and in dark phase by Kelvin it is yes you guess correctly C14. All right. Then after that all the scientist names I kept here children. Priestly mint plant engine house hydrillaa angel man cladophora green sulfur bacteria calvin chlorella hatch and slack sugar cane right then we talk about the chloroplast. Now this is something which you already heard in a chapter uh in your first year.
Chloroplast contain membrane envelope.
Outer membrane is more permeable than inner membrane. The space is called periplastial space. Stroma contain proteinous fluid. It has got many circular DNAs. Unlike mitochondria which has got circular one circular DNA. It contain all three types of RNA. Not all three types of RNA polymerase. All three types of RNA polymerase is there inside the nucleus. Such kind of questions you should be careful children. 70s ribosomes produce proteins. Enzymes of dark phase. Your textbook says carbon reactions are synonym for dark phase.
Remember that reduction of carbon dioxide to occur in stroma. So shall I say that both proteins and sugars are produced in stroma of chloroplast? Yes, enzymes work only in intact chloroplast.
If I isolate all the chloroplast, put it in a storehouse and can produce glucose by exposing them to light. Absolutely not. The enzymes turn volatile on isolation. Isolated chloroplast can perform light phase but not dark phase.
Remember that this is the diagram of chloroplast. All the philyloids grouped together to form granom. All right. So look at this is the philyloid. Thyloid and this are all the philyloids. This is said to be one granom. The space inside that is said to be the lumen.
And this thyloid which joins the two adjacent granom is said to be the stroma lame or stroma lam or stroma thyloid.
This is said to be the membrane system present inside the chloroplast.
All right. Graner a part of membrane system. It's a stack of philyloids. Gran represent a group of uh uh a a group of granom is called graner. Pigments are present on graner. Stroal lame. Just now I have shown you. All right. The two adjacent grana are joined by stroma lame. And you know this is very important. On this children on this grana there is both photos system one and photo system 2. Photo system one and photo system 2. Whereas on on stroma lamela there is only photo system one.
Now what is photo system? It's a group of pigments. All right. Here you see only photos system one. Whereas in these two you see both photo system one and two. Remember I repeat again granthyloids contain both photos system one and two whereas stroma lame will have only PS1 that is the reason non-cyclic electron transport is not seen there these are the points which you know it gran both PS1 and PS2 stroma only PS1 philyloid membrane is energy transducing membrane because it is impermeable to protons allow the proton accumulation on one side create a proton gradient. When you break this gradient, ATP synthesized. Therefore, we say energy transducing membrane. Could you answer in mitochondria? What is the energy transducing membrane? Yes. In a membrane of mitochondria is energy transducing membrane. What is the significance of light phase? There is a synthesis of ATP and an ADPH2. Good question. There is a division of labor within the chloroplast. Isn't it children? Light phase help in the synthesis of ATP and NADPH2 and dark phase job is to utilize this ATP and NADPH2 to synthesize glucose. So I'm going to give you two statements. Tell me which is correct. Light phase depends dark face depends on light phase.
Statement number two dark face depends on light. Which is correct? Dark face depend on light phase is correct. Dark phase depends on light is not totally correct because for dark phase no light is needed but dark phase depends on the products of light phase. That is an important point which you have to remember. Now this is a very u one area where you normally make mistakes. These are called tangential these are called longitudinal walls or radial walls. When the light intensity is low, the chloroplast are arranged with the flat surfaces facing light because they want to absorb more light. So therefore when the light intensity is less, how are the chloroplast? Chloroplast are perpendicular to this transverse walls perpendicular to this longitudinal walls perpendicular. I'm sorry I repeat again when the chlorop when the light intensity is less chloroplast are present perpendicular to this longitudinal walls or radial walls or parallel to the transverse walls. This is correct. One more way when the light intensity is high look at the chloroplast they are present parallel to the longitudinal or radial walls and they are perpendicular to the transverse walls. So it means that the chloroplast keep moving. They're dynamic depending on the light intensity. They tend to move from one orientation to another.
Different shades of green color is because of chlorophyll A, chlorophyll B, carotenoids and xanthophils. So chlorophyll A is blue green, chlorophyll B is yellow green, carotenoids is yellow orange, exantoils are yellow. Have you seen old and mature leaves children?
Yes, they are yellow because of eluted exanthtoil. Then keratenoid strictly speaking keratenoid is a combination of kerotin and xanthophil. What is the color of xanthophil? Yellow. What is the color of kerotene? Orange. So therefore yellow orange. Easy way to remember. And chlorophyll A is blue green and chlorophyll B is yellow green. Remember this. All these four pigments can be separated by a technique called paper chromatography.
Now let us talk a little bit about chlorophyll pigments. It's a lipid.
Remember that it is fat soluble because it's a lipid. It is water insoluble and it is seen in monera. In blue green alga you see chlorophyll. Whereas in some sulfur bacteria you see bacterial chlorophyll. It is also a type of chlorophyll but it is not truly chlorophyll. All right. Mona protestera and plants they contain what is this?
Chlorophyll. Blue green alga chlorophyll A only. Datoms and dinoflagillates A and C. You know that uglyoids A and B. Now we go to fungi no chlorophyll. Now we go to plants. Green alga A and B. Brown alga A and C. Red alga A and D. So start in higher plants it is A and B. So what about blue green alga A. So remember that those are the pigments which I've kept here. Yugenoids, green alga, brown alga, red alga. Alga is very unique in having all types of chlorophyll pigments. Higher plants A and B. The head of chlorophyll. Now if you look at this, it looks like a tennis racket. The head of chlorophyll is called pfirin head and the tail is said to be phytol tail and this head contain four rings and this four rings are said to be pyrol rings. The central element in this four rings is magnesium. It is joined to nitrogen present in this four pyrol rings. So this is pfiryin head and this is phytol tail. Just one remember one point you remember magnesium is present in the center. Chlorophyll is a chief pigment. All right. Chlorophyll a has absorption peaks in blue and red doia.
This is called absorption spectrum.
Observe here in blue light and red light. Chlorophyll A is absorbing large amount of wavelengths. In blue and red and in other wavelengths you could see the absorption of that is very less.
Blue and red absorption is more. What about chlorophyll B? Same blue and red absorption is more. But if you look at the peak children, chlorophyll B absorbs more blue when compared to A.
Likewise, chlorophyll A absorbs more red when compared to chlorophyll B. I repeat again. B absorbs more blue when compared to A and B abs and chlorophyll A absorbs more red when compared to B. But both of them absorbs more of blue and red. This is absorption spectrum. A graph which explains about different wavelengths of light absorbed by pigments. What about keratenoids? In the graph which is given, it is blue and green. It shows absorption peaks in blue and green caratenoids. You remember that also. I'm going to show you those grams.
Keratenoids, children, they're lipids just like chlorophyll. Just like chlorophyll, they're fat soluble. Just like chlorophyll, they're water insoluble. Keratenoids are yellow, orange. Absorption peaks. This is the point I was referring to. Blue and green.
They're accessory pigments. Which one?
Keratenoids and xanthophils are accessory pigments. I'm going to show you what are those accessory pigments.
They absorb light and transmit light to the reaction center and they protect the reaction center from getting photo oxidized. So these are the two jobs of accessory pigments. Both keratenoids and xanthophils does this job. Now let us talk about zanthophils just like keratenoids. They're lipids. They are fat soluble. They're water insoluble.
The color I told you is yellow lutein. I was talking about a a green sorry a yellow xanthophil which is present in old mature leaves.
Is it an accessory pigment? Yes. And it helps in wide range of light to be absorbed even uh keratenoids. It protects the reaction center from high intensities of light. This is the point which I was referring to. Brown algae is brown because of xanthophil called fcoanth.
This is an outside chance. Ficoillins.
They're water soluble proteins. This is interesting. Unlike chlorophyll and carotenoids which are water insoluble fats, ficcoilins are water soluble protein. The study of algae is fology.
So therefore ficoins are seen only in alga. Ficoeritthrine ficoyanin are the two types of pigments which are present in alga. Then we talk about action spectrum. We again talk about angle man.
He for the first time reported a graph which explains the rate of photosynthesis at different wavelengths of light. All right. Now look here children. This is it. Observe this. How do you know the rate of photosynthesis at different wavelengths of light? By the amount of product formed. What is the product which is liberated into the atmosphere? Oxygen. So by looking at amount how much amount of oxygen is liberated. One can easily tell the rate of photosynthesis. And look here it's very clear that in blue light and red light the rate of photosynthesis is more. We already discussed that. All right. Action spectrum peaks are there in blue and red. Then this is a very interesting graph. Did you observe that in your textbook children? Yes. Now observe here. This is the black colored one is the action spectrum which is the contribution of all the pigments. You should not say action spectrum of chlorophyll. There is nothing like action spectrum of chlorophyll.
Understand? And this uh blue colored one is the absorption spectrum of chlorophyll A. What did you observe?
I'll tell you three things. One, action spectrum and absorption spectrum of chlorophyll A are overlapping at the peaks.
Yes. What does it mean? It means that whichever wavelength of light chlorophyll A absorbs in large quantities at the same wavelength rate of photosynthesis is also more. It means that chlorophyll is achieve the headmaster. Yes or no? Then one more important point chlorophyll A and absorption spectrum of chlorophyll A and action spectrum are not exact one to one overlap. No doubt they are overlapping at peaks but it is not exact one to one overlap. What does it mean? It tells that other pigments also have a role to play. Other pigments look here a captain is an important person in a team.
Whenever captain plays the team normally wins normally not always isn't it? Same is the case here. Chlorophyll A is no doubt chief but doesn't mean that chlorophyll A alone controls the entire photosynthetic rate. It is not the case.
Look at this.
There is very less absorption of light by chlorophyll at this wavelength.
But look at rate of photosynthesis. It is not dropping to zero. What does it mean? other pigments are there which holds and allows photosynthesis to take place. So telling that peaks overlap to some extent is right. Telling that it is not exact one to one overlap is also right. I'm pretty sure that you understood this. This is the point which I've written here. Uh chlorophyle absorbs blue 420. Nice number. All right. and red strongly and these very wavelength also produce maximum photosynthetic activity. All right, that means that the peaks overlap. Action spectrum of photosynthesis and absorption spectrum of chlorophyll is not exact one to one overlap.
Photosynthesis is not driven by chlorophyll alone. It depends on the combined absorption of chlorophyll accessory pigments or one more way of saying accessory pigments broaden the action spectrum beyond the absorption spectrum of chlorophyll. Nicely I've written here this is a very important point to remember. Then we come to a concept of photo system already I was talking about what is the meaning of photosystem.
Photosystem is a cluster of pigments.
It's a group of pigments all right involved in photosynthesis. Now what does a photo system include? Photo system include a reaction center, a light harvesting complex, primary electron acceptor and some proteins and enzymes. All these four put together is said to be a photo system. Reaction center children always a chlorophyll a molecule. Light harvesting complex or antenna complex include not only chlorophyll A but chlorophyll B, carotenoids and xantoils. But when it comes to reaction center, it is chlorophyll. Your textbook says except one molecule of chlorophyll. They're referring to like that is reaction center.
The reaction center contain a special chlorophyll. uh actually is a pair but in your textbook they gave only one special chlorophyll a molecule capable of converting light energy to chemical energy. The light harvesting complex or antono complex include all four pigments. But these three are said to be accessory pigments. All right? Because they absorb light and transmit light to the reaction center. All right? The accessory pigments include chlorophyll B, carotenoids and xanthophils. What are the function of accessory pigments? It absorbs light and transmit light to the reaction center. Protect the reaction center from excessive light intensity.
This is a diagram which explains you the concept of photos system.
This is entire photo system. It contain chlorophyll A. Here I have shown two but take it as one chlorophyll A molecule.
This is light harvesting complex which absorb light and transmit light to the reaction center. And this is the primary electron acceptor which is also a part of photosystem. And you also see what is called the entire process taking place even in the presence of some proteins.
All these four put together you can call it as photos system. Uh this is not that much important in ryen's energy transfer excited. Look here if this is a pigment it's electrons are getting excited de excitation this energy is transported to the pigment number two. All right. So therefore in this way so not only pigment not only pigment directly absorbs light from outside but also some amount of uh energy is also transported from the previous pigment. So this is how the transfer of energy occur from one pigment to another. All right to naturally when the energy is lost when the energy is lost wavelength is going to what is called increase. So it is going to transfer to a pigment with higher wavelength is something which you know pretty well. Now we talk about photo system one and photo system two.
First photo system to function in non-cyclic is PS2.
Even though your textbook says both the photo systems operate simultaneously but photo system 2 operate little earlier than photo system one because it excites earlier. Discovery it is second. That is the reason why you call it as two.
reaction center is P 680 absorbs maximum light at 680. Some of you are thinking that it absorbs only at 680. No absorption maximize 680.
Normally it absorbs from around 650 to 680. All right. Chlorophyll A that is reaction center I'm talking about. So absorption maximize 680. That is the reason why it is said to be P680. It is located on granloid membranes only. PS2 is absent on stromal amal photo system one. It is the second photo system to function. It is discovered first. Reaction center is P700. It absorbs maximum light of 700 nanometers.
It is located both on granoids and also on stroma lame. This is interesting. PS1 is seen not only on stroma lame but also on the granloid.
Now we are in the last part of light phase where we look at how the light phase operate. All right. Now listen properly to what all I'm talking here. If at all you get a feeling that I went little fast, pause the video and and see it one more time. Surely you'll understand this. All right. So what is how we are going to talk about? Let me explain you this children uh in on a white page. Let me take a white page and explain you that will make your job more easier. Isn't it? Huh? Look here. What we do here children this topic I'll divide in into two or three installments. This non-cyclic electron transport we'll study in three installments such that it becomes more easier for you to follow. Right? Look here. This is a thyloid membrane.
Observe philyloid membrane. This is the thyloid membrane. And the space inside the philyloid membrane is said to be the lumen. Now listen carefully. All right, concentrate more. This is the philyloid membrane and the space inside that is said to be the lumen and this entire thing is stroma. So shall I put my hand like this and write all the three parts?
Yes. Now what are the all the three parts what are right here? This is said to be stroma. Yes. And this is said to be the philyloid membrane. Yes. And this is said to be the lumen up to here. No problem. Stroma. This is the philyloid membrane. And the space inside the thyloid membrane is lumen. S means stroma, thyloid membrane and lumen. Up to here there is absolutely no problem.
Now what I do is let me change the pen.
Right now I'll take a black one. So let me see if you can properly see it because on the white background black looks better. Now let us start with on the philyloid membrane you know pretty well on the membrane you see the presence of pigments. Just now I told you it contain photos systems. So therefore this is a photo system. Huh?
And the reaction center is P680. The reaction center is P680. Huh? Correct.
And there are other pigments also. Yes.
And they are accessory pigments. So shall I tell you a small equation? Photo system is equal to reaction center plus light harvesting complex.
reaction center plus light harvesting complex. Light harvesting complex is also called antenna complex and light harvesting complex or antenna complex include chlorophyll A, chlorophyll B, carotenoids and xantoils.
I exclude chlorophyll A. The remaining three are said to be accessory pigments.
I repeat again photos system or pigment system is equal to reaction center plus light harvesting complex. Now I break light harvesting complex into four. A b car keratenoid xantoll. I exclude a from that and the remaining three are said to be accessory pigments. Perfect. All right. Now it is going to absorb the light children in the form of photons.
What will happen now? When it absorbs light in the form of photons, electrons get excited.
And now it becomes P680.
I'm going to show you like this. This is an electron which is getting excited.
Look here. I am P680. When light hits me and also thanks to all the pigments which absorb light and transfer that light energy to me. So my electrons get excited. This is how it is.
This is the high energy electron. And what did you study? High energy means more unstable, isn't it children? So this P680 star is an excited form of this P680 with high energy electron. So what does it do? This is going to lose look here. This is going to lose its two electrons or one electron whatever maybe it's going to lose two electrons to a compound called fopitin.
This name is not given in your textbook.
They said primary electron acceptor.
They did not say what is the primary electron acceptor. This is focopon.
No problem. I'm P680. When light hits me, this is P680 star here. Then I'm going to donate the two electrons to fociton.
Now after donating two electrons to fopiten now the P680 star let me show you like this for convenience only only for convenience. Now it becomes P680 plus why because it has lost two electrons naturally. Now P680 plus all right now wants the two electrons and it asks fopitin can you give me two electrons.
Focitin says nothing doing I'm not going to give. Then p680++ gets worried I'm deficient of two electrons who is going to help me water says I will help you. So therefore this is going to help in the breakdown of water into two electrons two protons half water provided if it is one water.
If it is two water, four electrons, four protons and one molecule of oxygen. All right. Yes. Now this two electrons goes to P680 plus such that it can become P680. Now you understood P680 plus light P680 star.
P680 star becomes P680 plus after losing two electrons. P680 plus after gaining two electrons from water again becomes P680.
If somebody ask you which photo system is responsible for breakdown of water your answer should be PS2. I forgot to write you this is PS2. It operate first.
I told you no this is photo system 2.
This photo system is respon. One more question. Where does this breakdown of water occur? This breakdown of water occur on the lumen side. Lumen side. Is there any protein playing a big role here? Huh? There is a protein and this protein is oxygen evolving complex which is attached to the thyloid membrane back towards the lumen side which is playing a good role in this process. Everybody is happy. PSP68 is happy because it got two electrons and fopitin is happy because it got two electrons from this. Up to here there is absolutely no problem. What it happens here children is there is loss of two protons here and this two protons is going to increase the proton presence in lumen. What did you study in chemistry?
More protons means less pH or acidic. So the lumen starts becoming more and more acidic because of loss of protons from water.
This is called photois of water.
Manganesees and chlorine are the two important elements which are required for photosysis of water.
I'm going to stop here and go back and see what did I write. All right. With regard to this particular topic right now look here. Uh let me see what I have written here. Cello from here the first step in non-cyclic electron transport is absorption of light by photos system 2 light excites P680 of the reaction center this is totally correct I'll change the pen I'll change the pen to red all right then what the next one it is an uphill transport yes children 6680 to P680 star is surely an uphill because this has more energy Even compared to this, it's an uphill transport. P680 lose an electron and become oxidized.
P680 star lose an electron and become oxidized to P680 plus. The excited electron is then transferred to primary electron acceptor called fopitton.
Photoysis is a lightdriven process splitting of water into protons, electrons and oxygen. Where does it occur on the lumen side? How many photo systems are involved? Only one PS2.
These electrons lost from P680 must be replaced continuously. So water act as electron donor. Water gives electrons to P680 such that it becomes this oxygen evolving complex is involved minerals manganesees and chlorine. All right. Provide electrons to this. Add more protons to lumen decreasing the pH.
All right. So nice. We have reached up to here. This is the first part of non-cyclic electron transport. I'm pretty sure that you understood this without any problem. Then comes the next very important point. All right, which I'm pretty sure you have to concentrate here children. What will happen next?
Listen here. The two electrons from here. Shall I change the pen? Yes, I will do. All right. Now, it is going to lose the two electrons. The two electrons are lost from fopitin to a compound called plasto quon. Uh this is a very important compound. It is going to two lose two electrons to plastoone.
Plastoquinone is a lipidendi. So all this is thyloid membrane. What did you study you know in cytology? All right you studied that theloid membrane has contained lipids phospholippids. All right. Any membrane will have lipids and proteins just like plasma membrane. So the thyloid membrane contain lipids. Plastoinone is also a lipid. You are a lipid. I am a lipid.
You can go. So plastochinone can freely move. Hydrophobic. It can freely move within the lipid billayer. So it's mobile. It can move easily. Nobody's going to ask you ask plasinone where you're going, how where you're going. So plasquinone is always easy to move.
Otherwise this membrane is impermeable.
Be careful impermeable. But plasquin is an exception. It can move without any problem. Did all of you understood this?
Cello. It is accepting two electrons.
All right. Now, not only it accepts two electrons, it accepts two protons also.
From where? From the stroma.
Then naturally by accepting two electrons and two protons, plastoon is going to become plastool.
In organic chemistry you studied owns on reduction give rise to all. That's very simple. Now by accepting two electrons and two protons I am plastoinone. I accept two electrons from fopitton. I accept two protons from stroma. Now I have got two electrons and two protons.
I am free to move. So therefore what I do? I move from dash side. Look here.
This is the this is the membrane. Okay.
I move from dash side from the stroma side. I pick this is from stroma side. I move towards that side towards the lumen side. Ch I going to move up to here. I'm going to go up to here.
So this is PQ H2 plastool.
Why H2? Because it's accepting two electrons and two protons. Therefore P H2. So I'm moving from here to here. Who am I? Plasto.
What do I do later? After reaching here, I'm going to stand like that. On which side I am? I'm here on the lumen side.
On the membrane only, but on the lumen side. Why I'm standing? I'll tell you the reason. All right. I will wait. I will wait for what? I will wait for a compound called cytochrome B6F.
What does cytochrome B6F do? It is going to wake up. And what does it do?
Immediately it is going to pull. It is going to pull two electrons only only electrons from PQH2.
Once it pulls the two electrons from PQH2, its two protons now are more free to move and these two protons will be dumped into the lumin.
This is interesting. I repeat again PQ present towards the stroma side. I accept two electrons thanks to fopitton.
I accept two protons from stroma. Now I become pq2.
Now I tend to move on this membrane towards the lumen side. I'm free to move because the lipids are permeable. I'm a lipid. Phospholipids are there and thyloid membrane permeable. After reaching here I lose two protons and I lose two electrons.
Who is responsible for that? Cytochrome B6F. It says that I'll pull the two electrons from you. And it pulls two electrons. Once it pulls the two electrons, the two protons are lost.
What did you observe? Two protons are lost from dash to dash. Two protons are lost from stroma to lumen.
Question is how are these two protons moving? These two protons are moving through plastoinon. With the help of plastoinone the two protons are moving.
Question you're going to ask me is is plastoquinone acting as a proton channel? N does it act as a proton pump? No. Then how can it carry proton physically with his hands? It is physically carrying it.
Simple way of saying well in a lighter way I said but actually it is oxidation reduction. It's a chemical process which is actually carrying protons. So protons are carried chemically. All right? Not in the form of proton channel, not in the form of facilitated diffusion, not in the form of active transport, not even in the form of simple diffusion.
Then how I'm getting reduced here and I'm getting oxidized here. That's it. It is a reduction oxidation. So after getting reduced here, I have hydrogens's. I go here, I drop the hydrogens's means protons and then again come back here. So it means that it is a chemical process which is actually transporting protons from stroma to lumen via plastoino.
Who is the man of the match here for carrying protons from stroma to lumen?
Difficult, very difficult because there are two very fierce competitors. One is definitely plasquinone which is physically carrying protons. simple way proton carrier or hydrogen carrier because this is hydrogen's and one more competitor is cytochrome B6F by pulling the two electrons from PQH2 it is allowing the two protons to move into the lumen if you ask me both of them are joint winners let us be fair but we'll say one important statement PQ means plastoone is a proton carrier no problem there Proton carrier. It is moving from here to here. And cytochrome B6F is proton pump. Right word. Why proton pump? Because it is actually helpful in pumping protons into the lumen. Pump.
Some of you got it out. You said pump.
Yes, I said. All right. Then pump is a word used. You know water is pumped from lower to higher. So pump is a word used from lower to higher. Do you mean that there are low protons here and high protons here? Of course, high protons are here because protons are constantly added by breakdown of water. So there are more protons here. So protons are moving from low to high against the concentration.
That is the reason we require some energy. Protons have to move from low to high against the concentration. That is the reason we require energy. Not only that when there are more positive charge inside look here this mischievous positive charge protons doesn't want more protons to move to join once you get a seat in a bus you want the bus to move you don't want the other passengers to come all right same is the case here once the protons are here they don't want the remaining positive charge protons to move here so if at all you want to transport protons from here to here you have to do it with force Because there's a lot of resistance here. So not only there is a difference in concentration, there is also an electrochemical gradient which is between here and here. Isn't it? Charge difference, concentration difference.
Why concentration difference? Less protons, more protons. Why charge?
Less positive charge, more positive charge. And protons have to move to an area of more positive charge. Protons are also positively charged.
That is the reason this movement is said to be active means better way of saying it is against the concentration gradient. It requires energy.
Now the question you're going to ask me is who is going to provide the energy?
Very simple. The downhill movement of electrons listen carefully. The downhill movement of electrons is responsible for liberating energy. Now you understood what is the job of this chlorophyll molecule. The job of this chlorophyll molecule electrons get excited and its electrons getting deexited. Higher energy to lower energy from higher energy to lower energy energy get liberated.
You may ask me what I should do with this energy. Come on help in transport protons from stroma to lumen. This is easy to answer.
Your textbook also talks about the concept of redux potentials. Let me not talk too much of chemistry here but just I'll just touch and go here this topic redux potentials look here the meaning of redux potential is the ability to get reduced potential to get reduced look here when p680 star is going to fopit electrons move from fopitton to plasinone from here to here it means that pro electrons are moving from lower redux potential potential value containing compound to higher. Look here children if I want to pull something all right from the previous one I should have higher redux potential I should have more reduction potential then only I can pull isn't it yes so all these electron carriers are kept in the increasing order of redux potentials so let me give you imagine it is minus20 here all right so that is foponin then imagine this is zero here or maybe I put it as minus 10 here for convenience or this is zero here. What is it? Is it not increasing order of redux potentials?
Yes, because minus 10 is more than minus 20. Agreed?
If I take a difference of redux potentials and listen carefully difference of redux potentials - 10 -20 it comes to + 10. Now you understood the difference of redux potentials is positive. And what did you study in chemistry? The difference of redux potential if it is positive free energy will be negative. Yes or no? And you know that when the free energy is negative it is energy releasing process.
That is the reason energy is released in this downhill movement of electrons. So in two ways I explain in the language of higher energy of electron to lower energy. When the electron move from its higher energy to lower energy, energy is liberated. One more electrons are going to move from lower redux potential to a compound of higher redux potential.
Difference of redux potential is positive means free energy is negative means it's an exothermic reaction.
Energy releasing process. Ultimately if somebody ask you what the utility of this energy, utility of this energy is for the transport of protons from stroma to lumen.
It is taking a little time but I want you to understand this concept. Of course, you understood this concept. I want you to remember this concept thoroughly. Your tutor have explained all this nicely. It is this job is to read this topic such a way that there is no need for you to to read for more amount of time in the coming days. Look here. What did I write here? What did I write beyond this? We were we were we were up to here we read water. Now let me talk about plastoinone and cytochrome B6F here. What did I write here? I kept one or two white pages. All right.
Fociton is the primary electron acceptor. Correct. It is present on the stroma side of the correct. All right.
Then plastoinon very important. It is a lipid. It is hydrophobic. It can easily pass through the lipid billayer. It is a mobile hydrogen carrier because it accepts electrons and it accepts protons. Therefore, hydrogen it is mobile electron carrier moves from stroma side stroma side to the lumen side. It accepts electrons from fopitin.
It accepts protons from stroma side. PQ becomes PQH2. It moves towards the lumen side. It loses two electrons thanks to cytochrome B6F which pulls the two electrons. In this process the two protons are added to the lumen. All right. Protons are added not only by PQ but also by water.
Now look here. What did I write? Protons PQ not does not form a pore or a channel for protein transfer. It transfers protons from stroma to lumen by binding them chemically and carrying them as a part of PQH2. Totally clear. Why energy is needed to transport protons from stroma to lumen? Because of concentration difference and electrical gradient. Here I've written movement of protons from lumen is against the concentration gradient as high protons already exist in the lumen and further accumulation is energetically uphill and added to that when more protons enter into the lumen the lumen becomes electrically positively charged related to stroma. Positive charges repel other positive charges. Therefore incoming protons are electrostatically repelled.
So energy is needed to force more protons. Now you understood why energy is needed to carry protons from stroma to lumen.
And where from where this energy come from already I told you it is the downhill movement of electron or difference of redux potentials.
Light excise electron in PS2. These electrons now possess high free energy to low free energy. Hence electrons lose free energy. It helps in uphill transport of protons. In non-cyclic electron transport delta E the difference of the redux potential is positive because electrons move from a carrier with lower or more negative redux potential to one with higher or more positive redux potential. If delta E is positive then the delta G the free energy will be negative. Negative delta G means the free energy decreases. Hence energy is released spontaneously.
And let me talk about the cytochrome B6F complex. It helps in proton accumulation inside the lumen. PQ gets oxidized.
Two protons get liberated into the lumen. Two electrons from PQ is accepted by cytochrome B6F. And proton carrier is plastochinone. Proton pump. These two points are important. Proton carrier is plastochinone. Proton pump is cytochrome B6F. Both of them work together for the transport of protons from stroma to lumen. Cytochromes and iron containing proteins and cytochrome B6F oxidize PQH2 and it is going to reduce plastocyanin.
So the next electrons from cytochrome B6F children electrons from cytochrome B6F reach plastocyanin. So let me show you again this is electrons.
This is p680 star then to fopitin. Huh? then to plastoone.
gas plastoinone not only accepts two electrons but also two protons I'm sorry PQH2 PQH2 loses two protons into lumen then it loses two electrons to cytochrome B6F from here the two electrons goes to plastoion so this entire movement is downhill higher energy of electron to lower energy lower redux potential to higher redux potential. Higher energy to lower energy energy get liberated. The difference higher what redux potential to lower lower redux potential to higher redux potential the difference of redux potential is going is positive.
Therefore the free energy will be negative. Energy is liberated. Both this energy liberation will help in the movement of protons from low to high.
Now you understood why this electron transport should occur.
Plastocyanin hemocyanin gastrop ports blood pigment blue yes so it means that plastoscyanin is a copper containing electron carrier so why I'm why I brought hemocyanin understand that just like that copper here also copper in that way so it's not that related to that all right cytochrome it oxidized cytochrome B6F is it not pulling the two electrons from cytochrome B6F means oxidizing cytochrome B6F and reducing P700 is going to give the two electrons to P700 plus occur. It occur on the lumen side. Electron carrier is mobile electron energy from fopitin to plastoyanin from fopitin to plastoyanin higher to energy lower redux potential from fopitin lower to higher. This is uphill transport and P680 star to plasyin is downhill. These are points are very important to remember. I'm pretty sure that you understood this entire process.
Let me show you the diagram children with regard to this. That will help you to understand. This is photo system 2.
Again it all of you know this is photo system 2 P700. Again it is going to lose. It becomes P700 star. Then it becomes feridoxin reducing substance.
Then to feridoxin then to NADP. This is how it moves. All right. So again when P700 star loses two electrons it becomes P700++.
Now the plastoscyanin is going to give its two electrons to P700 plus. This is a what is called the photosystem 2 which is operating P700 star feridoxin reducing feradoxin and ultimately to NADP+. It absorbs reaction center is P700 discovery first absorption maxima at 700 located on granyloids and also on stroma lamealic P700 to P700 this is uphill to NADP plus downhill P700 donates electrons to feroxin reducing substance then accepts electrons from plastoyanin feroxin reducing substance it's an iron sulfa protein feroxin ultimately donates electrons to NADP P an enzyme remember FNR federoxin NADP reductase is an enzyme responsible for this location of FNR is on the stroma side look here this is the entire diagram you could see here this is the one we studied water is breaking up here all right first step is P680 it is losing electrons fopitin is somewhere here all right then it loses electrons to plastoone H we already discussed it It is accepting protons. Then PQH2 it is losing two protons and losing two electrons to cytochrome B6. From here to plastoyanin from plastosin the electron goes to PS1 to feridoxin and ultimately to NADP. So evolution of oxygen is on the lumen side. More proton accumulation is on the lumen side. Breakdown of water is on the lumen side. Synthesis of NADPH2 is on the stroma side.
All right. And this FNR enzyme is there on the stroma side.
All just this is very simple. Now more protons got accumulated. More protons got accumulated in the lumen. Isn't it up to here? No problem. Now what will happen? These protons which are there in the lumen will tend to move towards the stroma. Why? Come on. When there are more protons always system always will be from more to less. All right. When more protons are there they want to tend to move to an area where it is less. But this membrane thisoid membrane is impermeable to protons. That is the reason there is one carrier. This time it is acting as a facilitated diffusion carrier. This tail is acting as a channel for the movement of protons.
And when protons move from higher to lower, this is from lower to higher energy is needed. When the same protons move from higher to lower, energy will be liberated. And that energy liberated will help in the synthesis of ATP. This is said to be chemiosmosis. Here I'm going to explain you does that scheme of course include all this PS2 to primary electron acceptor primary electron acceptor to PS1 PS1 to primary electron acceptor primary electron acceptor to NADP+ products of non-cyclic electron transport is ATP NADP H2 and oxism and cyclic electron transport children let me show you here cyclic electron transport occur all right under conditions where a photo system is exposed to a wavelength greater than 680 or when there is a deficiency of NADP+ or when there is ATP synthesis needed but not NADPH2 cyclic can occur both on granal and always on stroma lame because there is no PS2 there. So in cyclic photos system loses electrons to feridoxin from feridoxin the electrons go back to plastoinone cytochrome B6f plastoyanin and again go back to the same photo system that is the reason why I say it's cyclic and in the cyclic electron transport there is no FNR involvement there is no NADPH2 there is no PS2 therefore there is no photosis of water and there is no evolution of oxygen only proton electrons get accumulated in the lumen when the same protons move through this coupling factor ATP synthesized. So the common product formed both in cyclic and non-cyclic is ATP. And the last part in light phase chemiosmosis scientist name is Peter Mitchell. It synthesis of ATP due to the breakdown of proton gradient.
It is applicable for both chloroplast and mitochondria.
What we require in chemiosmosis? We require an impermeable membrane. We require a proton gradient across the membrane. We require a proton carrier from stroma to lumen. We require a proton pump. And we also require a proton carrier from lumen to stroma. All these are needed for chemiosmosis. We already discussed all that. Why there are more protons? Because of photosis of water and active transport. Why there are less protons in stroma? Why there are less protons? There is a reduction of NADP and there is active transport.
Look here children. First I create a gradient. This is the thyloid membrane.
First I create a gradient very very less and very very high. Once more protons get accumulated in the lumen. Now on one fine morning I'll carry this protons from high to low just like in hydroelectric power from higher height when the water is dropped the turbines move energy is liberated. When a ball is rolled from a higher height energy is liberated the potential energy yes or no. So the difference so same way from when the protons move from higher to lower through this coupling factor when protons move from higher to lower energy is liberated and that energy is responsible for ATP synthesis. This is called photophosphorilation.
First I accumulate protons in the lumen thanks to water and plasquinone. Then after some time I carry these protons from lumen to stroma through coupling factor. The tail part of coupling factor act as a proton channel and because of this the head part is going to rotate because energy is liberated. This is called proton motive force and that rotation confirmational change will help in the synthesis of ATP.
This is the entire concept of ATP synthesis and CF knot CF1 this is the CF knot and this is CF1. So the CF knot act as a proton channel. When protons move from high to low energy get liberated and ATP synthesized in the head part.
This entire thing is said to be ATP synthes. The tail is CF not embedded in thyloid membrane head is CF1. It is on the stroma side. CF not help in facilitated diffusion channel for proton CF1 use this proton motive force to generate ATP. This is a nice diagram.
This is C of not and this is CF1 phase.
Here we see the production of glucose.
Then what we did in light phase is to synthesize ATP and NADPH2 because they are needed for dark phase.
So we produce all the raw materials needed. Now our job is to see the glucose synthesis without wasting any time. We'll get into it. It is called carbon pathway. We already discussed about this. It is temperature dependent because enzymes are involved. Enzymes are temperature sensitive in enzymes chapter you study.
It is dependent on the products of light phase not on light products of light phase. And they're high energy intermediates. Why you say intermediates? Because ATP and ADPH2 are surely intermediates because ultimately they produce glucose. All right, they're intermediates and that high energy intermediates be synthesized in light phase.
It is not dependent on light.
Now there is a proof immediately after light becomes unavable dark phase occur for some time till ATP and NADPH exhaust.
So it means that it is not dependent on light. It is dependent on light phase.
All right. Then occurrence it occurs in stroma of miso mostly. So Calvin children a scientist name he got Nobel prize in 1961.
Experimental plant is chlorella. Isotope used is C14. Sodium bicarbonate is the form of uh radioactive carbon which is injected into chloral C14. Chemical used to kill also hot methanol. What we did is what this man did is he added radioactive carbon in the form of sodium bicarbonate into alal cells. He allowed photosynthesis to take place for a certain period of time.
He dropped it in hot methanol.
photosynthesis stopped. By using auto radiography he was able to know the intermediate compounds. Again he took this al suspensions again he did the same. This time he increased the time of time of photosynthesis. In this way he decifered the entire Calvin cycle in 1961 along with Basham. He got a Nobel Prize.
Technique used to know the intermediate compounds is auto radiography and Benson and Basham are his associates.
and other contributions of Calvin light energy is converted to chemical energy during light phase and enhanced solar energy research as renewable source. All right. Now children there are two pathways of carbon dioxide fixation.
Your textbook clearly says about that one is C3 pathway a glucose is synthesized and one more in C4 pathway also a glucose is synthesized. So we'll start with the C3 pathway and the initial carbon dioxide acceptor is RUBP.
The first stable product is PGA and in C4 pathway it is P's initial carbon dioxide acceptor and the first stable product is oxyloistic acid. Let us start all right this Calvin cycle and let us see one by one. Now listen carefully. So we'll start this Calvin cycle and produce glucose. Let us see six molecules.
Six molecules of RUBP.
Six molecules of RUBP. Ribulos bif phosphate.
It's a 5carbon compound. I take six molecules of RUBP.
Okay. Then I add six molecules of carbon dioxide and six molecules of water.
And what is produced is 12 molecules of phosphoglyceric acid which is a threecarbon compound.
This is a very easy one. Six molecules of RUBP combined with six molecules of carbon dioxide and six molecules of water to form 12 molecules of RUBP.
And listen here, RUBP is a 5carbon compound. It's a keto sugar. Now I'm adding one carbon in the form of carbon dioxide. Then naturally it forms a sixcarbon compound, isn't it? It's going to highly unstable. It breaks into two threecarbon compounds. And this two three carbon compounds is PGA. So easy to remember. So it's very clear that RUBP is a five carbon plus one six carbon. It breaks into two three carbons. So 1 RUBP plus 1 CO2 produce 2 PGA. So 6 R U BP plus 6 CO2 will produce 12 PGA.
What is this step called? This step is called caroxilation phase.
What is an enzyme responsible for this?
The enzyme responsible for that is robiscoco. How many ATP utilized in this process? Zero. How many NADPH2 utilized in this process? zero. Let us see all the points with regard to coroxillation phase. All the points with regard to coroxillation phase.
It is the first and the crucial phase.
Yes. Initial carbon dioxide acceptor is a fivecarbon keto sugar. Yes. First stable product is phosphoglyceric acid which is a threecarbon non- sugar. Yes.
enzyme is rubp caroxilase.
It has oxygen activity as well but here it is not acting as oxygenase.
Number of Kelvin cycles needed to burn glucose is six because one CO2 is said to be one Kelvin cycle. So six Kelvin cycles has to operate in order to produce glucose.
This is the equation children. 6 Rub BP plus 6 CO2 and six water give rise to 12 PGA.
Substrate is keto sugar. Product is phosphoglyceric acid. No ATP used. No NADPH2 used. Perfect. That completes the first phase of Calvin cycle which is said to be caroxilation phase. Now let us go to the next phase children. What will happen in the next phase? Let us see what what we do in the next phase.
Look here what we did. We took six molecules of a RUBP.
Yes.
And we added six molecules of carbon dioxide and we produced 12 molecules of phosphoglyceric acid.
Let us do some calculations.
5 6 are 30 1 6 are 6 36 12 3's are 36 easy to remember absolutely no problem this completes the next phase that is said to be the caroxilation phase now let us talk about the next phase reduction phase what I do this 12 molecules of PGA listen here 12 molecules of PGA I convert to 12 molecules of phosphoglycerol deihide.
What did you study in your chemistry?
Acids is becoming alihide. When can acid become alihide? Only when you reduce it.
Reduction. So therefore reduction means what? Addition of hydrogens. So what I do is here I add 12 molecules of ATP and 12 molecules of NADPH2.
That's it. Look here children in PGA there are six CO2. Huh? This 6 CO2 present in PGA to that six CO2 present in PGA I'm adding hydrogens thanks to NADPH2 which is giving hydrogens to it.
So 12 pga contain this 6 CO2 to this 6 CO2 I'm adding hydrogen C H C H O that is nothing but PGA it's a sugar it's a trio sugar three carbon sugar it's a monossaccharide also called glycerol deihide phosphate and no prizes for guessing what is it called this is rightly called reduction ction phase because you are reducing this compound to this. It is not a singlestep process. It's a many step process. But in your textbook they have given in a short form reduction phase.
Let us read what is there under reduction phase. What did I what I have written under reduction phase. All right let us see reduction phase is the next step. I'll change the pen. All right.
Reduction phase. Please concentrate here. 12 PGL molecules are converted to 12 PGL in this 12 ATP and 12 NADPH2 are needed. All right. ATP needed for 6 CO2 in the reduction phase is 12. Correct?
12. ATP needed for one CO2 in the reduction phase will be two. As simple as it same way NADP for 6 CO2 is 12 and for one CO2 it is two. All right. And what the fast form triio sugar? The fast form triio sugar is PGL.
And how many PGL molecules we produce children? We go back. How many PGL molecules we produced? 12. You know what I do with this 12 PGL?
All right. I break it into two.
10 PGL and 2 PGL. Okay.
Now what I do with this 2pgl this 2 PGL I produce one molecule of glucose naturally because this is three carbon compound 2 3's are 6 1 6 yes I'm very happy that I produce glucose so out of 12 PGL I take 2 PGL and produce glucose you got a doubt why can't you take all 12 and produce six glucose why you're taking only two. There is a logic here.
Now each PGL is a threecarbon compound.
Yes. 10 PGL means 30 carbons. Yes. These 30 carbons are utilized in the regeneration of 6 Rubp 10 3 5 6 30. So now you understood 10 PGL.
First we have to keep it aside then only we can produce six rubp. If you can't regenerate rubp you can't continue the cycle for long that is the reason why we took only 2 pgl. So this is the reduction phase children and this is said to be the regeneration phase where 10 pgl are utilized in the regeneration of 6 rubp and I want to tell you here I use six molecules of ATP. So it's very clear.
Let us count how many ATP we produce in utilize in total. 12 + 6 18 ATP. And how many NADPH2 be utilized? 12 NADPH2. So 18 ATP and 12 NADPH2 are needed for how many carbons? 6 CO2.
For how many glucose? One glucose. So for 6 CO2, six calvin cycles, one glucose. we require 18 ATP and 12 NADPH2 one Calvin cycle or for one CO2 we require 3 ATP and 2 NADPH2 in the reduction phase number of ATP 12 and in the regeneration phase six for one CO2 in the reduction phase two in the regeneration phase one total three so let us just see what I what we have written all right with regard to reduction phase phase and regeneration phase. Children, we already went up to here. Yeah. 2 PGL out of 12 are utilized to produce glucose. Understood? 10 out of 12 PGL regeneration. You understood that PGL formed in Calvin cycle help in the synthesis of glucose, sucrose and ultimately starch. You know it.
Substrate for reduction phase PGA. It's not a sugar. Product is PGL. It's a sugar. ATP is 12 in the reduction phase.
12 in the regeneration phase. NADPH2 for 1 CO2 2 and two. Then we talk about the regeneration phase. Already I told you 10 PGL I utilize 6 ATP to produce 6 RUBP because 10 3es are 30 5 6 are 30.
Regeneration of RUBP is needed for continuity of this cycle. ATP needed is six but one ATP is needed. All right. For one CO2 substrate in the regeneration phase is PGL.
Product is RUBP. Is it true that both substrate and product are sugars? Huh?
All right. ATP used is six and NADPH3 used is none. So look at the cycle here.
I have written 6 CO2 plus 6 RUBP 12 PGA caroxilation phase 12 PGA 12 ATP and 12 NADPH to 12 PGL reduction phase two is utilized in the production of glucose and the remaining 10 PGL are utilized in the regeneration of 6 Rubp very nicely given 6 ATP are utilized here this is a repetition children 6 CO2 this much 1 CO2 is this much 6 C in coxulation phase zero. One C in coxulation phase natural will be zero.
Six C in the reduction phase 12 one C in the reduction phase 2. If they ask you reduction of CO2 one CO2 say three reduction phase means C2. So be careful about this. Six CO2 in the regeneration phase six one CO2 in the regeneration phase is one. Important statements about C3 plants. They are mostly mostly in temperate regions. Yes, C3 plants are mostly temperate. Temperature optimize is 20 to 25°.
They work because temperate regions children the temperature optimize is less. Temperature is less. Common example rice, wheat, potato, tomato, bell pepper. All right. And tomato. We come across this. All right. In factors, initial carbon dioxide RUBP. First stable product is PGM. It occur in the stroma of the chloroplast of misophil.
Star starch is synthesized in stroma of chloroplast. Rubiscoco act as both caroxilase and oxygenase. Location is in misoil cells. Is pep caroxilase observed in C3 plants? Yes. Is photorespiration seen? Yes. I'll tell you what is photorespiration.
All right. So these points uh you'll understand after some time effect of you'll understand after some time. Next carbon dioxide saturation point is around 450 ppm. Now what is this?
450 parts per million means for every 10^ 6 air molecules CO2 at 450 units for every 10^ 6 air molecules is CO2. So at 450 450 is the amount of CO2 present for every 10^ 6 molecules of air then max photosynthesis is reached in a C3 plant but atmosphere contain 03% means only around 350 ppm atmosphere contain 350 ppm saturation is at 450 ppm use a common sense it means that present level of carbon dioxide is surely less than what is needed for saturation that is the reason you grow the C3 plants in carbon dioxide enriched environment those are called greenhouse crops tomato and bell pepper we'll come across that all right many greenhouse crops then cranotum is absent chloroplast dimmorphism is absent number of caroxilations required is six no decarboxilations and number of cell types is only one nice it took a little time for me to get rid of Kelvin cycle But we discussed it perfectly. All right. Next time there should not be any confusion. Before I get into hatchlack cycle, first of all you have to understand the birth of hatchlack cycle is for what sake? Why hatslack cycle has to operate in some plants. So for that we should touch the concept of photoresiration first. So first we'll get rid of photorespiration children and then we'll come back to this the concept of hatchlack cycle. So let us see what is photorespiration. Let us see what is photorespiration just for a minute. Huh? This is the place where we talk about photorespiration.
Let me explain you this concept of photorespiration. First simple hardly it takes 2 minutes. Now listen carefully.
Imagine I have rubp molecule. Yes.
Now this time imagine oxygen is more not carbon dioxide interesting previously rub combined with CO2 enzyme name was rubiscoco now I'm rubiscoco I have got two active sides one for rubp one for either oxygen or CO2 when oxygen concentration is more oxygen will run and bind this place and competitively inhibit the binding of CO2 so therefore I can say this higher amount of oxygen act as a competitive inhibitor of RUBP caroxilase activity because caroxilase activity cannot occur when oxygen bind here oxygenous activity is seen that's it now listen carefully rubp is going to combine with oxygen because atmosphere contain more amount of oxygen when compared to CO2 then this will occur what did you study in your chemistry children any compound in the presence of oxygen has to break isn't it Yes. So therefore, RUBP is a 5carbon compound.
It breaks up into a 3carbon compound called phosphoglyceric acid and a twocarbon compound called phospho glycolic acid. Phosphoglycolic acid. A twocarbon compound called phosphoglycolic acid.
These are the two products formed.
3 + 2 5. This is five. Yes or no? Yes.
Up to here. No problem. Now shall I per are you going to permit me to take two molecules of RUB in place of one?
Okay, no problem. Two. Then natural A then how many PGA formed? Two phosphoglyceric acid. How many phosphoglycolic acid formed? Two. Yes.
Now listen because 3 2's are 6 2's are 4 6 + 4 10 5 2 are 10. No problem. Enzyme name RUBP oxygenase.
Now listen carefully.
This two molecules of phosphoglycolic acid. Look what happens. This is going to pass through a series of reactions.
pass through a series of reactions and form one molecule of phosphoglyceric acid and form one molecule of phosphoglyceric acid passing through chloroplast peroxyome mitochondria. These are the three cell organels.
Now let us count small two twos of four.
This is phosphoglyceric acid 3 means there is a loss of dash carbon dioxide.
There is also a loss of dash water just like in respiration.
Substrate substrate just like in respiration substrate plus oxygen just like in respiration produce water and CO2.
Yes or no? Huh? But unlike in respiration there is no ATP synthesis.
There is no NADPH2 synthesis.
Unlike in dark phase there is no sugar formation.
No ATP no NADPH2 no sugar. I repeat again five carbon two molecules 10 2 3's are 6 2's are 4. These two molecules of phosphoglycolic acid 2's are four. One CO2 is lost and the remaining three becomes one molecule of phosphoglyceric acid. Now use all your common sense and tell how many molecules of phosphoglyceric acid is formed. Let us see for two molecules. Two molecules here from here one three molecules.
So the number of phosphoglyceric acid molecules formed is three. Why we are counting? Because ultimately this PGA should form what? This PGA should form PGL and should form glucose by Calvin cycle.
Keep this in mind. How many PGA molecules formed in RUBP oxygenation?
Total three.
And what about RUBP fits get caroxilated children? How many PGA formed for two molecules? For six molecules of RUBP, it is 12.
For two molecules of RUBP it should be four. Ah now you got this. So two molecules of RUBP when it combines with two molecules of carbon dioxide that is Calvin cycle the number of PJ formed is four. 4 PGA 4 PGL glucose.
Then if the same two molecules of rubp combines with oxygen the number of PGA formed is 2 + 1 three only. So less PGA less PGL and less glucose. That is the reason why I say photorespiration is an unproductive process.
Shall I tell you one more reason why it's unproductive?
there is a loss of carbon in the form of carbon dioxide.
Added to that in this entire process there is utilization of ATP and NADPH2 to make things more worse.
That is the reason photorespiration is not an useful process.
And who is the villain here? Who should be blamed for photorespiration?
Please don't blame oxygen for that.
It is the enzyme rubiscoco which has a dual nature.
It is providing seed for CO2. All right, that's good. But it can also provide seed for oxygen if oxygen concentration is more than CO2.
So it is the rubiscocoite which is causing a problem for us. If rubiscoco says I absorb only CO2 I don't take oxygen then we wouldn't have seen this entire process the fact that this is going to absorb even oxygen means take even oxygen catalyze even rubp oxygenation that is the problem but if rubiscoco is a problem can we send rubiscoco out no Don't do that because without rubiscoco and without Calvin cycle we can never produce glucose.
The only way we can produce glucose is by using rubiscoco and other enzymes of calvin cycle.
Neither we can keep rubiscoco with us because quite often it is getting oxygenated.
Neither we can throw rubiscoco out because if we throw rubiscoco out there is no way we can produce glucose.
This is a very tricky situation isn't it children? Yes. Then three plants sugar cane maize sorghum. Shall I say SMS?
Huh? Sugar cane, maize and sorghum thought a lot for a long period of time.
They came out with a solution. You know what is the solution?
They ask rubiscoco and all the other enzymes of Calvin cycle.
Can you please change your place from misoil to bundle sheath?
Then the enzymes ask why we should change our place because bundle sheath cells are large. They are more green because there are more chloroplast and more importantly they are properly insulated with subarin. So you feel without any disturbance you can stay there.
All the enzymes of Calvin cycle which are normally present in misoil cells on the request of sugar cane maze and sorghum they all pack their bags and they go to bundle sheet cells. This is interesting. All right. Bundle sheath cells. Now let us see after all the Calvin cycle enzymes going to bundle sheet cells in sugar cane ma and sorghum how is the glucose produced and how is photorespiration prevented there this is the last topic for us to discuss concentrate what all I'm saying here all right this is the photo before we go to the photo uh the C4 pathway children before we go to C4 pathway let me see let us go through this photo respiration what I have written photorespiration is a light dependent process in which RUBP oxygenation occur leading to consumption of oxygen and release of CO2 without production of ATP or sugar.
It's a very marathon statement. I kept too many points there. Shall I make it break it and make it easy? Huh? All right. Time daytime. Yes. light high light intensities only in high light intensities there will be more oxygen release only when there is more oxygen release RUP oxygenation occur CO2 concentration is less oxygen concentration should be more and this occur only in C3 plants because I told you sugarce maze and sorghum have found out some way we don't know but found out some way to avoid photorespiration by asking all the calvin cycle enzymes to go to bundil she cells will We'll be talking about that story in 2 minutes.
Cell organises for this chloroplast, mitochondria and peroxyome. It is not useful. Rubiscoco act as oxygenase. High concentration of oxygen reduces the caroxilase activity. This is a competitive inhibition.
One rubp one oxygen. This is a fivecarbon compound breaking into a three carbon and two carbon.
Enzyme name oxygenase. that occur in chloroplast conditions highlight high oxygen and low CO2 same thing I take children for two molecules all right then two molecules of PGA and two molecules of phosphoglycolate or phosphoglycolic acid what will happen to this two molecules of phosphoglycolic acid it forms two molecules of glycine in peroxyome one molecule of serin in mitochondria ultimately one molecule of phosphoglyceric acid so it's very clear that this two molecules of phosphoglycolic acid all right is going to ultimately form one molecule of phosphoglyceric acid. So now count 2 PGA here 1 PGA. So total three PGA molecules are there for two molecules of RUBP. So the number of PJ formed will be three.
What is utilized in photorespiration?
ATP and NADH.
What is not produced in photorespiration? sugars ATP and it not produced. Why photorespiration is a wasteful process? For every two molecules of RUBP undergoing normal caroxilation, all right, the number of PGF formed is four. When the same two molecules of RUBP undergo oxygenation during photorespiration, the number of PJ formed is only three. Only three molecules of PJ are effectively recovered. One carbon is lost as CO2 children. We already seen less PGA, less glucose.
Added to that ATP and NADPH2 are consumed. No ATP is produced, no sugars.
All right. Now, at this point, don't talk about C4. Look at C3. CO2 fixation rate and high light intensities. I we'll discuss this after we discuss C4.
Children, is photorespiration okay? Yes.
Now we get into this the C4 pathway. We stopped our story by saying that all the Calvin cycle enzymes are asked to enter into bundle sheet cells by SMS plants.
Then what it will do in misophil? What it will do in misoil? Let us now look in misophil. It keeps six molecules of phosphoenol pyrovic acid.
This is a threecarbon compound. Yes or no?
No. RUBP six molecules of phosphoenol pyroic acid then it is going to combine with six molecules of carbon dioxide then it forms six molecules of oxalo acetic acid it is a four carbon 6 3's are 18 1 6 are 6 18 + 6 is 24 6 4 are 24 first stable product is a fourcarbon compound that is the reason it is called C4 cycle where this reaction occur not in bundle sheath misoil it occur in misoil cells this reaction occur in misoil cells what will happen to six molecules of oxyloic acid it may be transaminated to form six molecules of aspartic acid it is also a fourcarbon amino acid it's an acidic amino acid R is CH2CO BOH is aspertic. CH2CH2 COH is glutamic. You studied under biomolelecules. So oxyloic acid can be transaminated to aspartic acid.
Okay, leave it. It's not needed. It's not needed for us. Six molecules of oxyloic acid forms six molecules of malic acid. Naturally, this is the reduction process. I don't want to talk all that. This is also a fourcarbon compound.
Okay. Up to here no problem. First PP is absorbing CO2 and form oxyic acid. Oxyic acid is forming malic acid. What happens next? What happens next? This malic acid through plasmo decimator is transported to dash is transported to bundle sheet cells.
Yes. Bundle sheet cells. So a fourc carbon organic acid through plasmo desmitter. Why only plasma dismitter?
Because they're superized. I told you bundle cells are superin. Subarin is impermeable to water. So it forms malic acid. What will happen to the six molecules of malic acid. It forms six molecules of pyrovic acid.
And pyrovic acid is a dash carbon 3 carbon.
This is dash carbon. Four carbon. 6 4 are 24 6 3's are 18 there is a loss of six carbons that is in the form of 6 CO2 yes or no and I told you this reaction occur in which cells bundle sheet cells is rubiscoco there in bundle sheet cells yes can rubiscoco listen carefully can rubiscoco in bundle sheet cells get oxygen No. Why? Because walls are subverized.
Subarin is impermeable to water. Cork bottle caps are made up of cork. Have you ever seen? Because it prevents the entry of moisture from outside to inside. Because cork is made up of subarin. So rubiscoco site if I'm an enzyme rubiscoco one side is for rubp other is either other side is either for seo or oxygen. No way oxygen can reach because the entire walls are supervised.
So can photorespiration occur in C4 plants? Nah.
Then can Calvin cycle occur in C4 plants bundle sheet cells? Yes. How is CO2 passing through superized walls? No. If it oxen cannot enter even CO2 also cannot enter. Then how can Calvin cycle occur?
Malic acid runs through plasmo carrying this carbon dioxide into bundle sheet cell and liberate that CO2 to form pyrovic acid and that CO2 is accepted by RUBP. This is accepted by six molecules of RUBP to form 12 molecules of PGA.
It form 12 molecules of PGL. 10 and two.
This two molecules form glucose. This 10 molecules somewhere we have seen this.
Yes children you recollected correctly.
You're very smart. And this reactions are nothing but Calvin cycle.
Where is Calvin cycle occurring? Bundle sheet cells. Why? Because bundle sheet cells are properly supervised and rubiscoco site is never exposed to oxism.
Can dark phase occur in bundle sheath?
Yes. Calvin cycle occur in bundle sheath. All right. Then this pyroic acid it job is over. Now in the presence of ATP 12 ATP molecules form phosphoenol pyroic acid. You got it out. Six molecules by 12. In order to add six inorganic phosphates. In order to add one inorganic phosphate to one pyroic acid, I require energy of two ATP molecule breakdown.
ATP here is acting as energy donor note donor. Did all of you understood this?
Huh? two molecules of ATP first break liberate energy and that energy add one inorganic phosphate to pyrobic acid to form phospol pyroic acid finished how many ATP needed here 12 here 18 here total 30 ATP are needed in entire C4 pathway now I'm pretty sure that all of you understood this C4 pathway look at this atmospheric carbon dioxide accepted by PP forms a C4 acid C4 for acid malic acid first oxyloic acid oxyloic acid you say first stable product but I'm sorry to say that it is not stable the most stable form is malic acid that is the reason oxyaloestic acid is not transported instead malic acid is transported to bundle sheet cells all right this malic acid which is transported but if they ask you what the first stable product in C4 pathway for god's sake don't take malic acid you take oxyic acid only But when compared to oxaloistic acid, malic acid is more stable. That is the reason this C4 malic acid is transported to bundle sheet. It under go decarboxilation again to form what is called and that CO2 lost is accepted by RUBP and Calvin cycle. Kelvin cycle and this C3 acid what is this C3 acid pyroic acid is transported back into misoil and it is used in to form again phosphenol pyrovic acid easy way to remember just shall I tell you the easy way to remember this is PP this is forming oxyloic acid this is forming malic acid malic acid is transported and it is forming pyrovic acid pyrovic acid is transported back this is And this CO2 lost here is accepted. This is Calvin cycle. So all these reactions are in fact known to you. This is three carbon. This is four carbon. This is four carbon. This is four carbon. This is three carbon. This is three. So three carbon organic acid in this direction.
Four carbon organic acid from misoil to bundle sheet cells.
H nice. I'm getting exhausted here. All right. But I don't think you're getting exhausted because you're all very smart students. So you can easily understand all what all I'm saying. So we are winding up children. Last five minutes.
All right. Just we'll see about C4 pathway pathway. Definition it's an alternate pathway of carbon dioxide fixation occurrence in tropical SMS sugar cane maze and sorghum. Is it seen in India more or America? mostly India.
India is what? Subtropical. So therefore tropical or subtropical sugarce maze and sorghum and in tropical regions temperature is more. Yes. Carbon dioxide saturation is 360 ppm.
Atmosphere 360 ppm. Saturation means highest photosynthetic activity 360 ppm. So it means that the present level of carbon dioxide in the atmosphere is enough for a C4 plant to reach saturation. You need not enhance CO2 or you need not use a chopper to fumigate the fields with CO2 or in advanced countries we do it or grow them in a what is called green houses. It's not needed.
Common example sugar cane maze and sorghum. Initial carbon dioxide acceptor is PP. First stable product oxyloic acid operate in misoil and bundle sheath.
Primary caroxilation cytoplasm of misoil. Secondary caroxilation stroma of bundle sheath. Remember that PP caroxilation caroxilase in cytoplasm rubiscoco bundle sheath. Rubiscoco act as caroxilase only. Photo respiration is absent. productivity is high crayons anotomy the bundle sheet cells in the form of many rings this is called crayons it's a German word so one more language all right you know now that is German crayons means a group of bundle sheet cells in many rings all right arranged in many rings the bundle sheet cells are large their subarized walls contain more number of chloroplast PS2 is absent interesting why PS2 is absent if PS2 is there there is photosis of water. If photosis of water is there oxygen release will be there. Bundle sheet cells does not want any oxygen that is the reason they are soberized. So if PS2 is there in bundle sheet there is a chance for oxygen released that is the reason even the abandoned PS2 they are a granal chloroplast thyloids doesn't stack to form grana in bundle sheet. So chloroplast of misoil cell grana is seen calvin cycle enzymes are absent.
Chloroplast of bundle sheet cell grana is absent but contain the calvin cycle enzymes means within the same plant.
Misophil cell and bundle sheet cell are differing in chloroplast. Dorphism is seen in C4 plants.
PP CO2 oxyistic acid malic acid is transported CO2 Calvin cycle pyroic acid is transported back bond so nicely you explain all this all right that's about C4 pathway I don't think all these reactions are needed 6 PP 6 CO2 6 oxyloic acid remember only one point it occur in cytoplasm of misophil first stable product is this and the six oxyistic acid will be converted to six molecules of malic acid All right. Malic acid or aspartic acid either of them can enter the bundle sheet cells. Then this reaction is important. Six molecules of malic acid is converted to six molecules of pyroic acid. Decarboxilation carbon dioxide lost act by rubbp. Calvin cycle operate.
Decarboxilation and carboxilation both of them occur in bundle C cells. All right. Decaroxilation is prerequisite.
All right. For Calvin cycle to o occur.
So that's what it is. Secondary caroxilation occur in bundle sheet cells. Rubiscocoite is never exposed to oxygen. Rubiscocoite is always exposed to CO2. No chance for photorespiration.
18 ATP and 12 NADPH2 in bundle sheet.
Another 12 ATP misophil total 30 ATP.
All right. This is the 30 ATP. So now differences between C3 and C4. Rub primary electron acceptor C3. This is C3. This is C. This is C3. This is C4.
Okay. Primary carbon dioxide acceptor RUBP and then C4 PP. First stable product oxy first product PGA C3. Oxyloic acid C4.
Type of cells involved only misophil C3.
Misopil and bundle sheet C4.
Right. Next. Calvin cycle enzymes are present in misophil cells in C3. Bundle sheath cells in C4. Starch is synthesized in misoil cells in C3.
Bundle sheath cells in C4. Photo respiration is seen in C3 can never be seen because rubiscocoside is always exposed to CO2. C4.
Productivity less in C3 because of photorespiration. Productivity is more in C4 because there is no photo respiration. Oxygen play an inhibitory role C3. Oxygen can never play an inhibitory role C4.
Only one type of cell misophil C3 misophil and bundle sheath C4 cranottom is absent C3 present C4 chloroplast dimmorphism is absent C3 chloroplast dimmorphism is present C4 tomato bell pepper chlorella C3 majority of plants are C3 SMS no not the one what you're thinking sugarce maze and sorghum is SMS that is C4 all right temper ate plants is C3. Tropical plants are C4. Sugar cane tropical easy way.
Low low temperature optima. 20 to 25° is C3. 30 to 40° is for C4 because they are tropical.
CO2 saturation for a C3 plant is 450.
Don't think C350.
No. C3 450 and 4 350. All right. Be careful about this.
That's all Indi. That's about uh the differences between C3 and C4. You are extremely good in remembering all these points. That is very very simple. Now u we are about to wind up now. What is the last part? Factors affecting photosynthesis.
All right. Now when when we talk about the factors affecting photosynthesis children law of limiting factors the scientist's name is Blackman. What are the meaning of limiting factor? Any factor which is less than what is needed. is said to be a limiting factor.
All right. Process is controlled by suboptimum factor. That is the limiting factor. Now you know what Blackman said. Let me use in his own words.
If a process is conditioned it rapidity by several factors simultaneously then the rate of the process is controlled by the pace of the slowest factor.
Now this is very complicated. Shall I make it simple children? Huh? I'll do it. That is the reason I'm here. Now if a process like photosynthesis is controlled by several external factors because internal factors never act as limit. If several external factors simultaneously like CO2, light, temperature, water, then the rate of photosynthesis is decided or controlled by the factor which is present in less than the optimum quantities.
Did you understand what I said? That factor is said to be suboptimum factor.
Look here. Look here. Uh this is 0%.
This is 5% of sunlight. This is 10% of sunlight. This is 15% and this is 20% of total sunlight. Look here. As long as sunlight is in less than 10%. Look here.
The rate of photosynthesis is increasing increasing.
Then look here at 10% of total sunlight all right saturation is reached beyond that even if I increase the light intensity there is no increase so light saturation can be reached at 10%. So 10% of sunlight is enough to reach maximum saturation and maximum photosynthetic rate.
So look here light is acting as a limiting factor as as long as it is less than what is needed yes or no less than optimum that is said to be a limiting factor so shall I say which act as limiting factor here the x-axis is light light here light here light here light because all this is suboptimum 10% is saturation suboptimum here not light here not light here not light because it is more than s more than optimum.
So at this point at B and at C at B and C it could be CO2 most common limiting factor is CO2 or it could be temperature or it could be any other external factor. Did all of you understood this?
So this is said to be law of limiting factors. Most common limiting factor is carbon dioxide. Internal factors will never act as limiting factor. Nice. I explained nicely. All right. Now at low light intensity C3 and C4 plants respond to high CO2 concentration. At low light intensities neither C3 and C4 plants respond naturally. At low light intensity there is no ATP and ADPH2.
There is no synthesis of ATP and ADPH2.
There is no dark phase. Light saturation is reached 10%. We already discussed red light and blue light. This is 10% saturation. Beyond 10% there's no further rise. Most common limiting factor CO2 we already discussed C3 plants 450 CO2 saturation 350 what is parts per million I told you 350 carbon dioxide unit carbon dioxide molecules are present for every 10^ 6 air molecules that is the most common what is called carbon dioxide concentration in the atmosphere and CO2 saturation in C3 plants is 450 at 450 saturation is reached means you have to increase this and that is what greenhouse house crops is enhance CO2 temperature has a role both on light phase and dark phase because enzymes are involved. What are the two enzymes in light phase? FNR feridoxin NADP reductase and one more is ATP synthes coupling factor.
Water has more a role on plant rather than on photosynthesis. More water gut cells become turret sto opens more uptake of CO2 more photosynthesis. Same way more water leaf cells elongate more surface area of leaf more uptake of CO2 more photosynthesis. That's all that completes a chapter called photosynthesis. I said 1 hour but it took a little bit more time but no problem. I'm pretty sure that you are extremely good in revising this topic and thank you very much. We are going to meet with one more topic respiration in tomorrow's
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