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Difference between cyclic and non-cyclic photophosphorylation: Photosynthesis is the process of converting the light energy into chemical energy. The light energy collected during this process is used to convert carbon dioxide and water to glucose and oxygen. The entire process of photosynthesis is split into two parts: light reaction and dark reaction. The addition of a phosphate group during the light reaction of photosynthesis in the presence of light is known as photophosphorylation.
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Keyterms: Photosynthesis, light energy, chemical energy, carbon dioxide, glucose, oxygen, photophosphorylation, light reaction, dark reaction, phosphate group
Photophosphorylation
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Photophosphorylation is the conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) using light energy obtained through photosynthesis (ATP).
The transfer of the phosphate group to the ADP molecule in the presence of sunlight is the mechanism by which energy-rich ATP molecules are generated.
The addition of a phosphate group during the light reaction of photosynthesis in the presence of light is also known as photophosphorylation. In other words, photophosphorylation is defined as phosphorylation that occurs in the presence of light.
The photosynthetic light reaction takes place in the chloroplast of the grana. The light energy is transformed into chemical energy in the form of ATP and NADPH in this reaction. Photophosphorylation is a phenomenon that occurs when phosphate is supplied in the presence of sunshine or through the process of ATP generation by cells.
The energy produced in the light reaction is used to convert carbon dioxide into carbohydrates in the dark reaction of photosynthesis. This process takes place in the chloroplast stroma.
There are two types of photophosphorylation: cyclic photophosphorylation and non-cyclic photophosphorylation.
Read More: Photosynthesis in Higher Plants
Cyclic Photophosphorylation
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- Cyclic Photophosphorylation is the process in which ADP converts into ATP to generate energy for the immediate need of the cells.
- Only one photosystem (PS I) is used in cyclic photophosphorylation, and there is no decrease of NADP+.
- When Photosystem I absorbs light, the excited electron may enter an electron transport chain and make ATP.
- The de-energized electron then returns to the photosystem and completes the electron supply.
- NADP+ is not reduced as the electron returns to the photosystem, and water is not required to refill the electron supply.
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Non-Cyclic Photophosphorylation
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- Non-cyclic photophosphorylation is a process that uses the energy from the excited electrons produced by Photosystem II to cause non-cyclic electron movement to manufacture ATP molecules.
- The electrons lost by P680 of Photosystem II are occupied by P700 of Photosystem I and do not revert to P680, this process is known as non-cyclic photophosphorylation.
- The entire movement of these electrons occurs in a non-cyclic or unidirectional manner in this process.
- The electrons produced by the P700 are carried by the primary acceptor and subsequently passed on to the NADP via the non-cyclic photophosphorylation process.
- The protons H+ created when the water molecules split apart interact with the electrons to decrease NADP to NADPH. The reaction is depicted in the equation below.
NADP+ + 2H+ + 2e- → NADPH + H+
Difference between Cyclic and Non - Cyclic Photophosphorylation
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| Cyclic Photophosphorylation | Non-Cyclic Photophosphorylation |
|---|---|
| In the cyclic photophosphorylation process, photosystem I is involved. | The non-cyclic photophosphorylation process involves both Photosystem I and II. |
| Electrons move in a cyclic pattern. | Electrons do not travel in a cyclic pattern. |
| P700 is the active reaction centre in cyclic photophosphorylation. | P680 is the active reaction centre in non-cyclic photophosphorylation. |
| Electrons re-enter Photosystem I. | NADP accepts electrons from Photosystem I and does not return them. |
| ATP molecules are produced. | The molecules ATP and NADPH are both produced. |
| The cyclic photophosphorylation process does not require water. | The procedure necessitates the use of water, as well as the use of photolysis. |
| NADPH is not synthesized. | In non-cyclic photophosphorylation, NADPH is synthesized. |
| As a result, oxygen is not created as a by-product. | Oxygen is created as a by-product. |
| This method is ideal only in the case of bacteria. | This method works well with all green plants. |
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Things to Remember
- The light reaction and the dark reaction are the two processes in the photosynthesis process. The dark reaction is a light-independent reaction, whereas the light reaction is light-dependent reaction.
- The photosynthetic light reaction takes place in the chloroplast of the grana.
- The light energy is transformed into chemical energy in the form of ATP and NADPH in the photosynthesis light reaction.
- The energy produced in the light reaction is used to convert carbon dioxide into carbohydrates in the dark reaction of photosynthesis. This process takes place in the chloroplast stroma.
- The addition of a phosphate group during the light reaction of photosynthesis in the presence of light is known as photophosphorylation.
- Photophosphorylation is defined as phosphorylation that occurs in the presence of light.
- In cyclic photophosphorylation, electrons travel in Cyclic Pattern whereas electrons don't travel in cyclic pattern in non-cyclic photophosphorylation.
Previous Year Questions
- The Law of Limiting Factors was proposed by ______[KCET 2004]
- Emerson's enhancement effect and Red drop have been instrumental in the discovery of...[NEET 2016]
- The first carbon dioxide acceptor in C4-plants is….[NEET 1990]
- The first step for initiation of photosynthesis will be…..[NEET 2000]
- Photosynthetic Active Radiation (PAR) has the following range of wavelengths..[NEET 2005]
- Anoxygenic photosynthesis is characteristic of….[NEET 2014]
- During photorespiration, the oxygen consuming reaction(s) occur in -….[NEET 2006]
- Ferredoxin is a constituent of….[NEET 1991]
- In C4 plants, Calvin cycle operates in..[NEET 1989]
- In C4 plants, CO2 combines with...[NEET 1996]
- In Kranz anatomy, the bundle sheath cells have...[NEET 2011]
- In photosynthesis energy from light reaction to dark reaction is transferred in the form of :-….[NEET 2002]
- In photosynthesis, the light independent reactions take place at….[NEET 2015]
- Kranz anatomy is one of the characteristics of the leaves of...[NEET 2010]
- What is true for photolithotrophs?...[NEET 2001]
- Which is the first CO2 acceptor enzyme in C4 plants….[NEET 2000]
- With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct ?...[NEET 2017]
- Which pigment system is inactivated in red drop?...[NEET 2001]
- Which one of the following is wrong in relation to photorespiration ?...[NEET 2003]
- Which one of the following is essential for photolysis of water?...[NEET 2011]
Sample Questions
Ques: What are two types of photophosphorylation? (1 Mark)
Ans: There are two types of photophosphorylation: cyclic photophosphorylation and non-cyclic photophosphorylation.
Ques: For which case Cyclic photophosphorylation is ideal. (1 Mark)
Ans: Cyclic Photophosphorylation method is ideal only in the case of bacteria.
Ques: Complete the flowchart for cyclic photophosphorylation of the photosystem-I. (2 Marks)
Ans:
Cyclic photophosphorylation of the photosystem-I
Ques: Define photophosphorylation. (2 Marks)
Ans: The addition of a phosphate group during the light reaction of photosynthesis in the presence of light is known as photophosphorylation. Photophosphorylation is also defined as phosphorylation that occurs in the presence of light
Ques: Explain the process of non-cyclic photophosphorylation. (2 Marks)
Ans: The process of non-cyclic photophosphorylation occurs when electrons are released from the excited photo-centre and do not return. This process occurs only when both photosystems I and II are involved. Photolysis of water results in the release of electrons. So, a steady supply of water is required in this process. Both NADPH and ATP are generated during this process.
Ques: Give differences between Cyclic and Noncyclic Photophosphorylation. (5 Marks)
Ans: The following are some of the differences between cyclic and noncyclic photophosphorylation:
- Non-cyclic photophosphorylation occurs in both photosystems I and II, but cyclic photophosphorylation occurs only in photosystem I.
- Only ATP is produced in cyclic photophosphorylation, whereas both NADPH and ATP are produced in non-cyclic photophosphorylation.
- The electrons released by photosystem I are returned to the system in cyclic photophosphorylation. The electrons that are released by the photosystems in non-cyclic photophosphorylation do not return.
- Water is not photolyzed in cyclic photophosphorylation, but it is photolyzed in non-cyclic photophosphorylation.
- In cyclic photophosphorylation, oxygen is not released, while it is released in non-cyclic photophosphorylation.
- In cyclic photophosphorylation, water is not consumed. Water is consumed in non-cyclic photophosphorylation.
Ques: What are the important events and end products of the light reaction? (5 Marks)
Ans: Light reactions include the absorption of light, splitting of water molecules, oxygen release, and the formation of ATP and NADPH. The light reaction involves several complexes. The pigments are further arranged into two discrete photochemical light harvesting complexes (LHC) within the Photosystem I (PS I) and Photosystem II (PS II).
Photosystem I and Photosystem II do not function in the sequence of their name during the light reaction. The LHC is made up of hundreds of pigment molecules which are bound to proteins. Each photosystem has all the pigments forming a light harvesting system also called antennae. These pigments help in making the process of photosynthesis more efficient as it absorbs different wavelengths of light. The single chlorophyll molecule forms the reaction centre. The reaction centre is different in both PS I and PS II. In PS I, the reaction centre chlorophyll has an absorption peak at 700 nm, hence is called P700 . The PS II has absorption maxima at 680 nm, and is called P680.
Ques: Is it correct to say that photosynthesis occurs only in leaves of a plant? Besides leaves, what are the other parts that may be capable of carrying out photosynthesis? Justify. (5 Marks)
Ans: Photosynthesis does take place only in the green leaves of plants. The process of photosynthesis also takes place in other green parts of the plants. The mesophyll cells in the leaves have a large number of chloroplasts.
The chloroplasts align themselves along the walls of the mesophyll cells, so that they can get incident light.
- Photosynthetic or Assimilatory roots: They are green roots which are capable of PHS. For Example- Trapa bispinosa (water chestnut = Singhara), Tmospora (Gillow or Gurcha), Podostemum.
- Some plants modify their stems into flattened or fleshy cylindrical structures. These modified stems are called phylloclades. These stems contain chlorophyll and carry out photosynthesis.
- Cladode is also capable of carrying out the process of photosynthesis. Cladode is found in certain xerophytes, e.g., Ruscus and Asparagus.
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