Light Independent Reaction in Photosynthesis: What, How, Why and Detailed Facts

Photosynthesis is said to be the method by which the plants make their own food by use of sun, water and the carbon dioxide.

There is a concerned place called as stroma and is the place where light independent reaction in photosynthesis takes place. It has many enzymes that can work along with ATP and also NADPH to have carbon fixed.

Most of the life forms depend on the process of photosynthesis. This method is carried out by the plants, few type of bacteria, algae that help in capturing the energy from the rays to make oxygen and then store the chemical energy in the form of glucose which is a sugar. Herbivores tend to get the energy by consuming plants and the carnivores have it by eating the herbivores.

At the time of this, plants tend to take in carbon dioxide and also water from the soil and air. While at the inside of cells of the plant, there is oxidation of water which means that the electrons are lost and also at the same time the carbon dioxide are said to reduce themselves and then it gains the electrons. Due to this, the water is converted to oxygen.

light independent reaction in photosynthesis
Image credit-Light independent reactionWikipedia

With having the conversion of water into oxygen the carbon dioxide is also transformed to glucose. The plant tends to release the oxygen again in the air and then stores the rest of the energy in the molecules of glucose. There are chloroplasts inside the plant cell and they are small organelles. It helps in storing of the energy from the sun. Inside the thylakoid there is membranes as well that help the chloroplast.

There is light independent reaction in photosynthesis that does not need light and thus the pigment called to be as the chlorophyll, is not responsible for it as it helps in absorbing the light. At this time, the chlorophyll tends to absorb the energy from the red and blue waves and then reflects the green waves as well that makes it look green in color. There are both light independent reaction in photosynthesis and also light dependent one. 

What is light independent reaction in photosynthesis?

Photosynthesis is a common process to all the plants and is also vital at the same time that helps in making of food and gives energy to it.

There are many steps at the back of this method and thus it can be broken down into two of the vital steps being light independent reaction in photosynthesis and light dependent phase in photosynthesis.

The reaction that is dependent on light takes place in the thylakoid and needs the rays of the sun thus is called to be light dependent reaction in photosynthesis. The chlorophyll tends to absorb the energy from the waves of sun as light and the transfers it into the chemical energy in the form of the NADHP and ATP molecules.

Image credit-PhotosynthesisWikipedia

On the other hand, light independent reaction in photosynthesis is called to be Calvin cycle and takes place in the stroma which is in between the membrane of thylakoids and the membrane of chloroplast and does not need light and thus called to be light independent reaction in photosynthesis. During this phase, energy from the NADPH and ATP molecules are used to assemble the molecules of carbohydrates like glucose from carbon dioxide.

Not all the forms of them are made to be equal for photosynthesis. There are several types of photosynthesis available that include the light independent reaction in photosynthesis and also the dependent one along with the C4 and C3 photosynthesis. Majority of the plants use up the method of C3. At the time of Calvin cycle they make a three carbon product called 3 phosphoglyceric acid that becomes glucose.

On the other part, C4 makes a four ring carbon product that is intermediate and then spits into the carbon dioxide and also again into a three form compound at the time of Calvin cycle. The best of C4 is that it gets to make a good level of carbon and then allows the plants to sustain in the surrounding with not much use of the water or light. C3 is concerned to be called as the Calvin cycle.

Where does light dependent reaction take place in photosynthesis?

The chloroplast is surrounded by a membrane that is of type double and has an outer line and also an inner membrane. This is equal to that of mitochondria.

The light dependent reaction is seen in the thylakoids. The reaction takes place while the pigments of chlorophyll are seen inside the membranes of thylakoids that help in getting energy from sun.

The motif of this light dependent reaction is to gather a lot of energy from the dun and then break it down to molecules of water to make NADPH and ATP. The molecules tend to store energy and these are used up in the light independent reaction in photosynthesis. Chloroplasts are the pigments that are green and seen in the chlorophyll.

Chloroplast are the one that help in absorbing the light from sun. It is kept in the membranes of thylakoids and in the protein complex that is called the photosystem 1 and photosystem 2. The series of reaction that are light dependent starts when the sun hits the molecule of the chlorophyll and is seen in photosynthesis 2. This gets the electron excited and then leaves the molecule of chlorophyll.

Image credit-ThylakoidsWikipedia

After leaving the molecule they are seen to travel along the membrane of thylakoids through the series of carrier proteins which is called the electron transport chain. At this time, photosynthesis 2 gets the water molecules to be spitted up to have the lost electron gained back and then fills up the energy vacuum that is made by it. This method is used up by the humans but has failed in the labs. Each of the water molecules tend to break down into two molecules of hydrogen and only one for the oxygen.

Oxygen is released as a product that is of no use with it being assembled to join again. The ions of hydrogen are made up in more concentration in the lumen of thylakoids. They tend to pass via the enzyme called as ATP synthase and then the move provides the energy that is needed to ass to the third of the ADP phosphate to make ATP. This energy is needed for make cell methods with also glucose being broken to make ATP later after respiration.

Where does light independent reaction take place?

The inner part of the chloroplast also has other membrane and is the thylakoid membrane that is folded in many forms linked to stacks of the discs.

The light independent reaction in photosynthesis takes place inside the stroma. It has many enzymes that help in the work of NADPH and also ATP and then has the carbon fixed from the carbon dioxide in the molecules that shall be built in the glucose.

The very goal of thelight independent reaction in photosynthesis is to gather the glucose molecules. This is a part of the food making process that needs carbon dioxide that is given by air to the plants. The plants get the carbon from CO2 and then makes the glucose blocks. An enzyme within the stroma is called as rubisco that bind with the five carbon molecule of the RubP linking itself to the carbon dioxide molecule.

This tends to make a molecule of six carbons that is broken again into the molecules of three carbons. This is the part of the light independent reaction in photosynthesis that is called to be carbon fixation. After this, the carriers of energy take up the light dependent reaction for its contribution. NADPH and ATP shares each of the 3 phosphoglycerate an atom of hydrogen and then makes two molecules of the simple sugar called the G3P. Finally, the molecules are used to make glucose.

Image credit-StromaWikipedia

This part of the light independent reaction in photosynthesis is sued up for carbon and also called as reduction. Calvin cycle uses up 6 molecules of carbon di oxide a single time and this shows that there are 12 molecules of the G3P that is made. Despite this, there are only two of the molecules that is sued to make glucose molecule and the rest of them are said to be recycled back to RubP so that this cycle can run again.

How is ATP produced in the light reactions?

The method is said to complete itself y sue of two other process in the field of the light reaction with one making ATP and other NADPH.

The proteins tend to diffuse outside the thylakoid via ATP synthase that gets to make ATP. One the electron reaches the PSI then it links the chlorophyll with a unique pair and then re excite it by absorbing light.

Electrons tend to transfer in a chain between the two type of photosynthesis with the photosynthesis 1 serving to make NADPH and then the second one making the ATP. In the light independent reaction in photosynthesis and also the other one, water is spitted to make a serve for the electrons and then give off oxygen in the form of byproduct ATP is made from ADP by adding of phosphate.

Protons diffuse out of the thylakoid lumen through the enzyme, ATP synthase, producing ATP in the process. Once the electron reaches PSI, it joins its chlorophyll a special pair and re-excited by the absorption of light. During the process of photosynthesis, light penetrates the cell and passes into the chloroplast. The light energy is intercepted by chlorophyll molecules on the granal stacks. Some of the light energy is converted to chemical energy.

Image credit-ATP SynthaseWikipedia

During this process, a phosphate is added to a molecule to cause the formation of ATP. In light reactions, water is split, providing a source of electrons and giving off O2 as a biproduct. H+ electrons from water reduce NADP+ to NADPH. Light reactions also generate ATP from ADP by adding a phosphate. The main function of light-dependent reactions of photosynthesis is to produce ATP molecules through oxidation-reduction reactions and chemiosmosis reactions in chloroplasts.

How are ATP and NADPH used in photosynthesis?

At the reactions, the sunlight is sued as energy and use the get the water oxidizes and then passes the electrons to NADP making NADPH.

In simple terms, both of these are made by the process called as electron transport chain. At the time of the light reactions, water is used and makes oxygen. This takes place at day as needs the sun.

Some of energy from light is used to have ADP converted to ATP. The ATP and NADPH are made subsequently and then sued as a power to have the sugar made at the time of Calvin cycle. Both of the ATP and NADPH are made together. Photosynthesis takes place in two stages that drives the sunlight to synthesize NADPH and ATP.

Image credit-ATPWikipedia

In a process called non-cyclic photophosphorylation (the “standard” form of the light-dependent reactions), electrons are removed from water and passed through PSII and PSI before ending up in NADPH. This process requires light to be absorbed twice, once in each photosystem, and it makes ATP. ATP can be used to store energy for future reactions or be withdrawn to pay for reactions when energy is required by the cell.

Animals store the energy obtained from the breakdown of food as ATP. Likewise, plants capture and store the energy they derive from light during photosynthesis in ATP molecules. NADPH is an electron carrier that accepts a pair of high-energy electrons and transfers them, along with most of their energy, to another molecule. NADPH plays a big role in the light-independent reaction when it is used, along with ATP, to produce high energy sugars.

Role of ATP and NADPH in the Calvin cycle

The very simple step function of these are to make electrons, generate energy and then also make hydrogen atoms in the Calvin cycle.

ATP is said to be the source of energy and while the NDPH gets to reduce the agent that adds to the light energy electrons t make sugar. The Calvin cycle makes three of the carbon molecules and the also G3P.

The two of the vital roles are to have the light dependent phase and the light independent reaction in photosynthesis to work together and also act as a energy source to have the energy taken away from the sun to have the light independent reaction in photosynthesis help itself to make food for itself. Some of the Calvin cycle needs ATP and other needs NADPH.

Image credit-NADPHWikipedia

This reaction is catalyzed by the enzyme rubisco. In the second stage, six ATP and six NADPH are used to convert the six 3-PGA molecules into six molecules of a three-carbon sugar (G3P). This reaction is considered a reduction because NADPH must donate its electrons to a three-carbon intermediate to make G3P. Both of these molecules carry energy; in the case of NADPH, it has reducing power that is used to fuel the process of making carbohydrate molecules in light-independent reactions.


I am Ankita Chattopadhyay from Kharagpur. I have completed my B. Tech in Biotechnology from Amity University Kolkata. I am a Subject Matter Expert in Biotechnology. I have been keen in writing articles and also interested in Literature with having my writing published in a Biotech website and a book respectively. Along with these, I am also a Hodophile, a Cinephile and a foodie.

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