Frizzaayy
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Can someone please explain non cyclic photophosphorylation and the calvin cycle and the link between them as simply as possible? The Edexcel book explains uit in such a complicated way, I'm so stuck
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RMNDK
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(Original post by Frizzaayy)
Can someone please explain non cyclic photophosphorylation and the calvin cycle and the link between them as simply as possible? The Edexcel book explains uit in such a complicated way, I'm so stuck
Non Cyclic Photophosphorylation
  1. A photon excites a chlorophyll molecule in photosystem (PS) II. Electrons are raised to a higher energy level and are carried off to PSI.
  2. The photon is also used to split water into H+, O2 and e- which is called photolysis. The electrons replace the excited ones. Oxygen is released as a waste product. H+ is used in step 3 and 5.
  3. When those electrons are carried off to PSI, they lose energy as they fall back to a lower energy level. This energy is used to actively transport protons (H+) from the stroma to the thylakoid lumen. The protons move back into the stroma via ATP synthase. Every 3 protons catalyses the phosphorylation of ADP to ATP. This is how ATP is produced.
  4. A photon excites a chlorophyll molecule in PSI which releases electrons. Along with H+ it is used to reduce NADP+ to NADPH
Calvin Cycle
  1. You start with RuBP (Ribulose Bisphosphate).
  2. CO2 enters the leaf through the stomata and into the stroma.
  3. It combines with RuBP using the enzyme Rubisco (Ribulose Bisphosphate Carboxylase) which forms a 6-carbon compound intermediate
  4. This is unstable and immediately breaks down into two 3-carbon compounds. They're called GP (Glycerate-3-phosphate)
  5. THE LINK: Non-Cyclic Photophosphorylation produces ATP and reduced NADP (NADPH). Energy from ATP and reduced NADP is used to reduce GP to TP (Triose Phosphate).
  6. Every 5 out of 6 molecules of TP are used to regenerate RuBP. This is done by using energy from ATP. The cycle repeats.
  7. The molecules of TP not used for regeneration go onto form carbon compounds e.g. glucose, cellulose, starch, etc
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Frizzaayy
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(Original post by RMNDK)
Non Cyclic Photophosphorylation
  1. A photon excites a chlorophyll molecule in photosystem (PS) II. Electrons are raised to a higher energy level and are carried off to PSI.
  2. The photon is also used to split water into H+, O2 and e- which is called photolysis. The electrons replace the excited ones. Oxygen is released as a waste product. H+ is used in step 3 and 5.
  3. When those electrons are carried off to PSI, they lose energy as they fall back to a lower energy level. This energy is used to actively transport protons (H+) from the stroma to the thylakoid lumen. The protons move back into the stroma via ATP synthase. Every 3 protons catalyses the phosphorylation of ADP to ATP. This is how ATP is produced.
  4. A photon excites a chlorophyll molecule in PSI which releases electrons. Along with H+ it is used to reduce NADP+ to NADPH
Calvin Cycle
  1. You start with RuBP (Ribulose Bisphosphate).
  2. CO2 enters the leaf through the stomata and into the stroma.
  3. It combines with RuBP using the enzyme Rubisco (Ribulose Bisphosphate Carboxylase) which forms a 6-carbon compound intermediate
  4. This is unstable and immediately breaks down into two 3-carbon compounds. They're called GP (Glycerate-3-phosphate)
  5. THE LINK: Non-Cyclic Photophosphorylation produces ATP and reduced NADP (NADPH). Energy from ATP and reduced NADP is used to reduce GP to TP (Triose Phosphate).
  6. Every 5 out of 6 molecules of TP are used to regenerate RuBP. This is done by using energy from ATP. The cycle repeats.
  7. The molecules of TP not used for regeneration go onto form carbon compounds e.g. glucose, cellulose, starch, etc
Thank you so much, this is really helpful!
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jake123254
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I think cyclic occurs only in photo system 1. The electrons that become excited pass along the electron carriers to the ATP synthase and then back to the chlorophyll they left. No water has to be broken down and no electrons replaced. The electron carriers are associated with a H+ ion channel, or proton. When the electrons pass across the carrier, protons are transported through the protein associated with it. This causes a build of protons inside the thylakoid space as they move from the stroma. There is now a gradient of protons inside the thylakoids and so they willl diffuse back out again. They do this through a channel associated with an ATP synthase enzyme. The flow of protons is called chemiosmosis and the kinetic energy from this is used to produce chemical energy by producing ATP from ADP and P. This is then used in the light-independent stage.


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jake123254
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Oops I didn't read your question properly haha


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