Cyclic and Noncyclic Phosphorylation MDCAT Quiz: Cyclic and non-cyclic phosphorylation are two events involved in the light-dependent reactions of photosynthesis that take place within the thylakoid membranes of the chloroplasts. While both of them result in the production of ATP, they differ in pathway, electron flow, and the extra molecules formed. These processes play a critical role in providing the energy and reducing power required for the light-independent phase (Calvin Cycle). It is very essential for MDCAT students to understand these mechanisms to enable them to tackle questions regarding photosynthesis and the production of energy.
Cyclic Phosphorylation
In cyclic phosphorylation, electrons excited by sunlight in photosystem I (PSI) are cycled back to the same photosystem. Only photosystem I is involved in this process, and neither NADPH nor oxygen is produced. The electrons pass through an electron transport chain, creating a proton gradient that drives ATP synthesis through photophosphorylation. Cyclic phosphorylation is especially important when the cell needs more ATP than NADPH or when NADP⁺ is scarce.
Noncyclic Phosphorylation
Noncyclic phosphorylation involves both photosystem II (PSII) and photosystem I (PSI) and is the primary pathway in the light-dependent reactions. Here, electrons excited in PSII are passed through an electron transport chain, generating ATP, and are then transferred to PSI. Electrons from PSI are used to reduce NADP⁺ into NADPH, a molecule essential for the Calvin Cycle. To replenish lost electrons in PSII, water is split in a process called photolysis, releasing oxygen as a byproduct.
Test Your Knowledge with an MDCAT Quiz
Take the MDCAT Quiz on Cyclic and Noncyclic Phosphorylation to find out how well you understand the differences and importance of these processes. It will also include the role of photosystems, the production of ATP and NADPH, and the splitting of water during photolysis. You can improve your performance in answering questions from this section in MDCAT with frequent practice.
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Free Flashcards for Quick Revision
Free Flashcards on Cyclic and Noncyclic Phosphorylation: a very concise summary of the main processes and distinctions between the pathways. They emphasize photosystems’ role, the products formed, and conditions favoring each type of phosphorylation and are an excellent tool for quick review and last-minute preparation for the MDCAT exam.
Mastering the concepts of Cyclic and Noncyclic Phosphorylation comes in handy while understanding the mechanisms of energy production in photosynthesis. Use our quizzes and flashcards to increase your knowledge and ace your MDCAT preparation!
What is the main difference between cyclic and noncyclic phosphorylation?
Electron flow in cyclic phosphorylation returns to the photosystem
In cyclic phosphorylation, where do the electrons travel?
Back to the photosystem
Which of the following is produced during noncyclic phosphorylation?
ATP and NADPH
Which photosystem is involved in cyclic phosphorylation?
Photosystem I
What is the final electron acceptor in noncyclic phosphorylation?
NADP+
What happens to the electrons in cyclic phosphorylation?
They return to the photosystem I
Which of the following processes produces oxygen?
Noncyclic phosphorylation
What is the role of ATP in noncyclic phosphorylation?
To power the Calvin cycle
What is the major product of cyclic phosphorylation?
ATP
What molecule is produced as a byproduct of noncyclic phosphorylation?
Oxygen
In noncyclic phosphorylation, which molecule is reduced?
NADP+
What is the primary purpose of cyclic phosphorylation?
To produce ATP
Which of the following is involved in both cyclic and noncyclic phosphorylation?
Photosystem I
In noncyclic phosphorylation, what is the role of photosystem II?
To absorb light and excite electrons
How does ATP production in cyclic phosphorylation compare to noncyclic phosphorylation?
It produces less ATP
Which of the following is true for cyclic phosphorylation?
It only involves photosystem I
How many molecules of ATP are produced per electron pair in cyclic phosphorylation?
One
What happens to the electrons after they leave photosystem I in cyclic phosphorylation?
They return to photosystem I
Which process requires both photosystem I and II?
Noncyclic phosphorylation
What molecule is produced in cyclic phosphorylation but not in noncyclic phosphorylation?
NADPH
In noncyclic phosphorylation, where is oxygen produced?
In the thylakoid membrane
What happens to the protons pumped during cyclic phosphorylation?
They create a proton gradient
In which phase of photosynthesis does cyclic phosphorylation occur?
Light-dependent reactions
What is the electron transport chain's role in cyclic phosphorylation?
To generate ATP
How does the electron flow in noncyclic phosphorylation differ from cyclic phosphorylation?
It moves to NADP+ instead of returning to the photosystem
In noncyclic phosphorylation, which molecule is the source of electrons?
Water
How is the proton gradient used in both cyclic and noncyclic phosphorylation?
To drive ATP synthesis
What happens to NADP+ in noncyclic phosphorylation?
It is reduced to NADPH
In cyclic phosphorylation, what is the role of photosystem I?
To excite electrons and send them through the electron transport chain
Which of the following best describes the role of the electron transport chain in cyclic phosphorylation?
It passes electrons between photosystems
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