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Questions and Answers
What are the primary products of photosynthesis?
Which of the following best describes the Calvin cycle?
In which part of the chloroplast does the Calvin cycle take place?
Which statement accurately describes the light-dependent reactions?
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How do photosynthesis and cellular respiration relate to each other?
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Which of the following is NOT a reactant in the photosynthesis process?
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What role does water play in photosynthesis?
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During photosynthesis, which molecule is ultimately produced through the fixation of carbon dioxide?
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What is the primary purpose of the light-dependent reactions in photosynthesis?
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Which component within a photosystem is responsible for losing an electron when excited?
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What occurs during resonance energy transfer in a photosystem?
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In non-cyclic photophosphorylation, where do the electrons ultimately come from?
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What distinguishes Photosystem II (PSII) from Photosystem I (PSI)?
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Which of the following statements about light-harvesting complexes is correct?
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What is the result of light absorption during non-cyclic photophosphorylation?
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Which photosystem primarily interacts with the electron transport chain following PSII?
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What is the initial role of light energy in photosystem II?
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What molecule is produced as a byproduct from the splitting of water during photosynthesis?
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What process harnesses the flow of protons to synthesize ATP?
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During the light-dependent reactions, where does the high-energy electron travel after leaving photosystem II?
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What is the primary function of NADPH in photosynthesis?
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Which pathway does not result in the formation of NADPH?
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How is ATP produced during the light reaction phase of photosynthesis?
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What happens to the electron that is lost from P700 in photosystem I?
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Study Notes
Photosystems
- Photosystems contain proteins, pigments, and chlorophylls, and function to harvest light
- Photosystems are optimized to capture light energy
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Light-harvesting complexes:
- Contain proteins and pigments like chlorophylls
- Capture light energy
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Reaction center:
- Contains a special pair of chlorophyll a molecules (often called the special pair)
- The special pair can lose an electron when it absorbs light and pass it to the primary electron acceptor
Photosystem Types
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Photosystem II (PSII):
- Special pair: P680
- Primary receptor: Pheophytin
- Source of electrons: Water molecules
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Photosystem I (PSI):
- Special pair: P700
- Primary receptor: A0
- Source of electrons: Electron transport chain from PSII
Non-Cyclic Photophosphorylation
- Definition: The movement of electrons from water to NADPH through PSII and PSI, generating ATP.
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Requires sunlight absorption twice:
- Once in each photosystem
- Products: ATP and NADPH
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Process:
- Electrons are removed from water molecules
- Electrons are passed through PSII and PSI
- Electrons end up in NADPH
Cyclic Photophosphorylation
- Definition: Electrons cycle back to the first part of the electron transport chain, repeatedly cycling through PSI.
- Does not generate NADPH: Electrons are routed away from NADP+ reductase.
- Products: ATP
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Process:
- Electrons flow down the electron transport chain
- Protons are pumped into the thylakoid interior
- Electrons return to the first part of the electron transport chain
Light Absorption of PSII
- Energy is passed from pigment to pigment until it reaches the reaction center
- Energy is transferred to P680 and boosts an electron to a high energy level
- The high-energy electron is transferred to an acceptor molecule
- The special pair's electron is replaced with an electron from water
- Splitting of water releases oxygen as a byproduct
Light Absorption of PSI
- The electron arrives at photosystem I and joins the P700 special pair of chlorophylls
- Light energy is absorbed by pigments and passed to the reaction center
- The special pair's electron is boosted to a very high energy level and transferred to an acceptor molecule
- The special pair's missing electron is replaced by a new electron from PSII (arriving via the electron transport chain)
Electron Transport Chains
- Release energy as electrons move through
- Energy is used to drive pumping of H+ ions into the thylakoid interior.
- The H+ gradient created is then used to make ATP
ATP Synthesis
- The flow of H+ ions through ATP synthase generates ATP from ADP and phosphate
- This process is called chemiosmosis
NADPH Formation
- The high-energy electron travels down a short second leg of the electron transport chain
- The electron is passed to NADP+ (along with a second electron from the same pathway) to make NADPH
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Description
Test your knowledge on the roles of photosystems in light absorption and energy conversion. This quiz covers the structure and function of both Photosystem I and II, as well as the process of non-cyclic photophosphorylation. Perfect for students studying plant biology or photosynthesis.
