AP Biology reference on the light-dependent reactions of photosynthesis: thylakoid structure, chlorophyll, photosystems I and II, photolysis, electron transport, NADPH, and photophosphorylation.
Subject: biology
How do the light-dependent reactions directly contribute to the subsequent light-independent reactions (Calvin cycle) in photosynthesis?
Answer: They generate ATP and NADPH, providing the chemical energy and reducing power for carbon fixation.
The light-dependent reactions convert light energy into chemical energy stored in ATP and NADPH. These energy carriers are then released into the stroma and are essential for driving the Calvin cycle, where carbon dioxide is fixed into carbohydrates.
What is the immediate consequence of water splitting by the oxygen-evolving complex in Photosystem II?
Answer: It provides electrons to replace those lost by P680⁺ and releases protons into the thylakoid lumen.
In Photosystem II, water undergoes photolysis, releasing electrons to replenish P680⁺, protons into the thylakoid lumen to contribute to the proton gradient, and oxygen as a byproduct.
A plant cell is performing cyclic electron flow. What is the most likely reason for this, and what are its direct products?
Answer: The cell requires additional ATP without increasing NADPH; it produces only ATP.
Cyclic electron flow is a pathway where electrons from Photosystem I are returned to the cytochrome b₆f complex, generating additional ATP. This pathway does not produce NADPH or oxygen, making it useful when the cell's ATP demand exceeds its NADPH demand.
How does the absorption of light energy by pigment molecules ultimately lead to the reduction of NADP⁺ to NADPH?
Answer: Excited electrons from P700 are passed through an electron transport chain involving ferredoxin, leading to NADP⁺ reduction.
Light energy absorbed by pigments is transferred to the reaction center P700 in Photosystem I, exciting an electron. This high-energy electron is then passed through ferredoxin and ultimately used by NADP⁺ reductase to reduce NADP⁺ to NADPH.
How is the proton motive force established across the thylakoid membrane, and what is its primary role in ATP synthesis?
Answer: It is established by the splitting of water and proton pumping by the cytochrome b₆f complex, driving ATP synthase activity.
The proton motive force (electrochemical gradient) is built by two main processes: the release of protons into the thylakoid lumen from water splitting in PSII, and the active pumping of protons into the lumen by the cytochrome b₆f complex. This gradient then drives ATP synthesis as protons flow back through ATP synthase.
The process by which plants, algae, and certain bacteria convert light energy into chemical energy stored in glucose is called {0}.
Answer: Photosynthesis
Photosynthesis is the overall process of converting light energy into chemical energy.
The thylakoid membrane contains protein complexes involved in the {0}.
Answer: light reactions
The light-dependent reactions are also referred to as the light reactions.
The light-dependent reactions of photosynthesis occur in the {0} of chloroplasts.
Answer: thylakoid membranes
The thylakoid membranes are the specific location within chloroplasts where the light-dependent reactions take place.
The light-dependent reactions of photosynthesis occur within the {0}.
Answer: chloroplasts
Chloroplasts are the organelles where photosynthesis takes place.
The light-dependent reactions produce the chemical energy carriers {0} and NADPH.
Answer: ATP
ATP (adenosine triphosphate) is one of the key energy carriers produced during the light-dependent reactions.
The enzyme NADP⁺ reductase catalyzes the reduction of NADP⁺ to {0}.
Answer: NADPH
NADPH is a reducing agent produced in the light-dependent reactions, used in the Calvin cycle.
{0} is the principal pigment that absorbs light energy in photosynthesis.
Answer: Chlorophyll
Chlorophyll is the primary pigment responsible for absorbing light energy in plants.
{0} is the first protein complex in the light reactions, containing P680.
Answer: Photosystem II
Photosystem II (PSII) initiates the electron flow in the light-dependent reactions.
To replace the electron lost by P680⁺, photosystem II splits water in a process called {0}.
Answer: photolysis
Photolysis is the splitting of water molecules by light energy, which provides electrons for Photosystem II.
The {0} transfers electrons from photosystem II to photosystem I through a series of carriers.
Answer: electron transport chain
The electron transport chain moves electrons between photosystems, contributing to the proton gradient.
{0} contains a reaction center called P700, which absorbs light most strongly at 700 nm.
Answer: Photosystem I
Photosystem I (PSI) is involved in the final steps of electron transfer to NADP⁺.
The pathway where electrons flow from water through photosystem II, the electron transport chain, photosystem I, and finally to NADP⁺ is called {0}.
Answer: noncyclic electron flow
Noncyclic electron flow is the primary pathway that produces both ATP and NADPH.
In {0}, electrons from photosystem I are returned to the cytochrome b₆f complex instead of being passed to NADP⁺.
Answer: cyclic electron flow
Cyclic electron flow generates additional ATP without producing NADPH or O₂.
The synthesis of ATP during the light reactions is called {0}.
Answer: photophosphorylation
Photophosphorylation is the process of ATP synthesis driven by light energy during photosynthesis.
An electrochemical gradient called the {0} is established across the thylakoid membrane due to proton accumulation.
Answer: proton motive force
The proton motive force is the energy stored in the electrochemical gradient of protons across the thylakoid membrane.
{0} is a transmembrane protein that allows protons to flow back from the thylakoid lumen into the stroma.
Answer: ATP synthase
ATP synthase uses the energy from the proton gradient to synthesize ATP.
The mechanism by which ATP is formed as protons pass through ATP synthase is called {0}.
Answer: chemiosmosis
Chemiosmosis describes the process where ATP synthesis is coupled to the movement of protons across a membrane.
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