Complete Process of Photosynthesis Study Guide


Photosynthesis is a process by which plants produce food using chlorophyll present in them and combine it with carbon dioxide in water and sunlight. This process is essential for plants to sustain themselves. Indirectly this process produces food for all living beings; therefore, we must understand the photosynthesis process.

Photosynthesis Process

The photosynthesis definition in biology explains that they occur in plants by which plants absorb light energy and then convert them into chemical energy. During this photosynthesis process, energy transforms the water, carbon dioxide, and other minerals into oxygen and other organic compounds.

Importance of Photosynthesis

There is a certain significance of photosynthesis, such as:

  • Photosynthesis helps plants to store light energy as chemical energy.
  • These chemical energies are used by animals and human beings when they consume plants, and thus, indirectly, plants become the source of food and energy for them.
  • Enables the plants and different organisms to form the base of the food chain.
  • Due to the process of photosynthesis, plants consume carbon dioxide and leave out oxygen in the atmosphere, because of which we survive the atmosphere.

Phases of Photosynthesis

Photosynthesis process

1. Absorption of light

The very first step of the process of photosynthesis is the absorption of light by chlorophylls. These chlorophylls are connected with proteins in the thylakoids sack of chloroplasts. Moreover, the absorbed light converts itself into energy, and then it is used for eliminating the electrons from the water, which is an electron donor to form oxygen. Then, these eliminated electrons pass to a major electron acceptor known as Quinine.

2. Transfer of electron

After the transfer of electrons to the electron acceptors, they get transferred to the final electron acceptor, an NADP positive. They are transferred by the process known as the chain of electron transfer, in which the molecules exist in the thylakoid membrane.

3. Production of ATP

When electrons are transferred to the final acceptor, it moves out to the stroma of the plant from the thylakoid lumen by the complex process of F0F1. This results in the production of ATP, which is the most important source of energy in a plant’s biological process. This ATP production is solely utilized during synthesis and is dependent on light.

4. Carbon fixation

The formed NADP and ATP produce the energy. The process of reducing carbon occurs by the electrons into the six-carbon molecules. All the above three steps are known as light reactions, while this carbon fixation is light-independent, and thus, they are called dark reactions. This process is also known as the Calvin Cycle.

Formula of Photosynthesis

The process of photosynthesis is expressed in a chemical equation as

This formula of photosynthesis explains that the reactants, which are six carbon dioxide molecules and six water molecules, get converted into six molecules of oxygen and sugar molecules using the light energy captured by chlorophyll.

What is Light Reaction?

  • The light reactions occur within the thylakoid of the chloroplast. Special pigments absorb light energy and transfer it to high energy electrons eventually producing ATP and the electron carrier NADPH.

  • The light reactions use two photosystems, called photosystem 1 and photosystem 2, which are both embedded in the thylakoid membrane.

  • These photosystems are named in the order they were discovered not for the order in which they participate in the photosynthetic process. The light reaction actually begins in photosystem 2.

  • The first thing that happens is that the photosystem 2 receives photos, or light energy. This light energy is transferred to a chlorophyll reaction center causing electrons in the reaction center to become energized. These electrons become so energized that they escape photosystem 2 and move to a nearby electron acceptor molecule, located in the electron transport chain.

  • Meanwhile, to replace the electrons leaving photosystem 2, water is split, releasing oxygen, two hydrogen ions and two electrons. The first set of electrons continues to move down the electron transport chain, releasing stored energy as it moves. This energy is used to create a hydrogen ion gradient.

  • A protein in the electron transport chain pumps hydrogen ions from the stroma into the thylakoid space. This creates a high concentration of ions in the thylakoid space, relative to the low concentration of ions in the stroma. This gradient contains a large amount of potential energy which is used by an enzyme called ATP synthase.

  • The hydrogen ions flow down their concentration gradient, through a channel in the ATP synthase, releasing energy in the process. ATP synthase uses this energy to add a phosphate to ADP forming ATP.

  • The light reaction produce both ATP and NADPH. As photosystem 1 absorbs additional light energy, the electrons again become energized, escaping photosystem 1 and moving down the second electron transport chain.

  • Electrons from the electron transport chain adjacent to photosystem 2, replace those in photosystem 1. And again, water is split to replace the electrons that have moved from photosystem 2. At the end of this electron transport chain the energized electrons and a hydrogen molecule are used to reduce NADP to NADPH.

  • Together, the ATP and NADPH formed during the light reactions, are used by the Calvin cycle reactions. The important thing to remember is that plant needs both light and water to survive. Without these ingredients, the light reactions would shut down stalling photosynthesis and causing the plant to die.


  • Photosynthesis is how plants produce food in the presence of water and sunlight.
  • The different phases of photosynthesis are: Absorption of light, Transfer Of electrons, Production Of ATP, and Carbon Fixation.
  • The formula of the process of photosynthesis can be written as: 6CO2 + 6H2O → C6H12O6 + 6O2


1. What is the step-by-step process of photosynthesis?

There are generally four steps of the photosynthesis process.

  • Absorption of light
  • Transfer Of Electron
  • Production Of ATP
  • Carbon Fixation

2. What are the 10 detailed steps invloved in photosynthesis?

Step 1. The first step of photosynthesis is Light-dependent. The three main components of this step are water, carbon dioxide, and sunlight. Carbon Dioxide and water enter the leaf, and the sunlight is absorbed to produce energy in the whole process.

Step 2. It is also a light-dependent process. Here, the chloroplasts of green color tend to bend towards the sunlight.

Step 3. Light independent and thus known as a light reaction. The chlorophyll inside the chloroplasts begins to absorb light.

Step 4. Light-dependent light strikes the pigment of the thylakoid membrane, where the water splits into oxygen.

Step 5. Light-dependent step and in this step oxygen gas gets released in the atmosphere.

Step 6. It depends on the light, and the enzymes get converted from ADP to ATP and NADP into NADPH whenever the sunlight hits the other pigment molecules of the thylakoid.

Step 7. In light reactions, chlorophyll turns off and releases the energy for dark reactions, ATP, and NADPH.

Step 8. Light independent step; Carbon dioxide gets attached to the rubisco, i.e., an acceptor in the chloroplast.

Step 9. This step is light-independent and known as a dark reaction; the produced energies, like ATP and NADPH, are used in the Calvin cycle to convert CO2 from the atmosphere into the six-carbon sugar glucose.

Step 10. Light independent step. In the Calvin cycle, three molecules of carbon dioxide get converted into glucose from the atmosphere, and these are stored in the plants in the form of food.

3. What happens during process of photosynthesis?

Carbon dioxide and water are converted into glucose and oxygen.

4. What is the process of photosynthesis?

Photosynthesis is the process by which plants use sunlight, carbon dioxide, and water to produce energy and oxygen in the form of sugar. This sugar is stored by plants as food or starch.

5. What are ADP and NADP?

ADP is Adenosine phosphate, and NADP is Nicotinamide adenine dinucleotide phosphate.

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