Podcast
Questions and Answers
What is the primary role of photosystems I and II in the light reactions of photosynthesis?
What is the primary role of photosystems I and II in the light reactions of photosynthesis?
- To break down ATP into ADP and inorganic phosphate.
- To synthesize glucose directly from carbon dioxide.
- To absorb light energy and convert it into chemical energy. (correct)
- To transport water molecules to the Calvin cycle.
During the light reactions, water molecules are split. What are the direct products of this process?
During the light reactions, water molecules are split. What are the direct products of this process?
- Glucose, oxygen, and ATP
- Electrons, carbon dioxide, and water
- Electrons, oxygen, and protons (hydrogen ions) (correct)
- Carbon dioxide, ATP, and NADPH
How does the cytochrome complex contribute to ATP production during the light reactions?
How does the cytochrome complex contribute to ATP production during the light reactions?
- By directly synthesizing ATP from ADP and inorganic phosphate.
- By transporting protons into the thylakoid lumen, creating a proton gradient. (correct)
- By donating electrons to NADP+ to form NADPH.
- By capturing carbon dioxide and incorporating it into organic molecules.
What is the role of NADP+ in the light reactions of photosynthesis?
What is the role of NADP+ in the light reactions of photosynthesis?
How is a proton gradient established across the thylakoid membrane during the light reactions, and why is it important?
How is a proton gradient established across the thylakoid membrane during the light reactions, and why is it important?
What is the function of ATP synthase in the light reactions?
What is the function of ATP synthase in the light reactions?
If a plant were exposed to a toxin that inhibits the function of Photosystem II, which of the following would be directly affected?
If a plant were exposed to a toxin that inhibits the function of Photosystem II, which of the following would be directly affected?
Which of the following energy conversions occurs during the light reactions of photosynthesis?
Which of the following energy conversions occurs during the light reactions of photosynthesis?
What is the relationship between the thylakoid lumen and the stroma in the context of ATP production?
What is the relationship between the thylakoid lumen and the stroma in the context of ATP production?
How do ATP and NADPH contribute to the Calvin cycle after being produced in the light reactions?
How do ATP and NADPH contribute to the Calvin cycle after being produced in the light reactions?
Flashcards
Photosystems
Photosystems
Protein-pigment complexes that absorb light and convert light energy to chemical energy by exciting electrons and shuttling them along the thylakoid membrane.
Chlorophyll
Chlorophyll
Light-absorbing pigment in Photosystem II that gets struck by photons of light, exciting electrons to a higher energy level.
Cytochrome Complex
Cytochrome Complex
A complex that transports additional protons into the thylakoid lumen using energy from excited electrons.
NADP+
NADP+
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ATP Synthase
ATP Synthase
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Light-driven electron transport chain
Light-driven electron transport chain
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Study Notes
Thylakoid Membranes and Light Reactions
- Thylakoid membranes contain specialized molecules that work together to perform the light reactions
- Photosystems, protein-pigment complexes, absorb light
- Photosystem I and Photosystem II are the two types of photosystems
- Photosystems convert light energy to chemical energy
- This conversion occurs by exciting electrons and shuttling them from molecule to molecule along the thylakoid membrane, forming an electron transport chain
Process of Light Reactions
- Photons of light strike chlorophyll, a light-absorbing pigment, in Photosystem II
- Electrons in the chlorophyll are excited to a higher energy level
- Excited electrons are passed to an electron carrier
- Water is split, releasing electrons to replace those lost in Photosystem II
- Oxygen is produced as a byproduct and released into the air by the splitting of water molecules
- Protons (hydrogen ions) are released into the thylakoid lumen as well
- Excited electrons move to the cytochrome complex
- The cytochrome complex uses some of the electron energy to transport additional protons into the lumen
- A protein inside the lumen receives electrons from the cytochrome complex and passes them to Photosystem I
- Electrons that are passed to Photosystem I have lost most of the energy gained from light in Photosystem II
- Photons of light hit chlorophyll in Photosystem I, re-exciting the electrons
- The electrons are then passed to a third electron carrier
- The electrons interact with an enzyme and NADP+ (the final electron acceptor) to form NADPH
- Some of the light energy is now stored in the reduced molecule NADPH
- Some of the energy released from the transfer of electrons establishes a proton gradient across the thylakoid membrane
- Protons accumulated in the lumen diffuse into the stroma through ATP synthase
- ATP synthase uses the potential energy of the proton gradient to combine ADP with inorganic phosphate to form ATP
- Potential energy is transformed into chemical energy stored as ATP
- ATP and NADPH now store energy from the light reactions, which can be used in the Calvin cycle
- This light-driven electron transport chain, which is usually continuous in the presence of sunlight, encompasses a series of chemical reactions that involve light absorption, energy conversion, and electron transfer carried out by the photosystems and other enzymes on the membrane of the thylakoids
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Description
Learn about thylakoid membranes and light reactions. Photosystems, protein-pigment complexes, absorb light and convert light energy to chemical energy. Excited electrons move to the electron transport chain. Water is split, releasing electrons and oxygen.
