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Questions and Answers
What are the main products generated by the light-dependent reactions of photosynthesis?
What are the main products generated by the light-dependent reactions of photosynthesis?
- Glucose and O2
- ATP and glucose
- NADPH and O2
- ATP and NADPH (correct)
In which part of the chloroplast do the light-independent reactions occur?
In which part of the chloroplast do the light-independent reactions occur?
- Inner membrane
- Thylakoid membranes
- Granum
- Stroma (correct)
Which of the following statements is true regarding carbon fixation?
Which of the following statements is true regarding carbon fixation?
- It requires ATP and does not involve NADPH
- It occurs exclusively in the light-dependent reactions
- It produces glucose directly from sunlight
- It integrates CO2 into carbohydrate molecules (correct)
What role does chlorophyll play in photosynthesis?
What role does chlorophyll play in photosynthesis?
What is the primary function of the ATP produced during photosynthesis?
What is the primary function of the ATP produced during photosynthesis?
Which process describes the conversion of solar energy into chemical energy during photosynthesis?
Which process describes the conversion of solar energy into chemical energy during photosynthesis?
Which of the following compounds is reduced during the light-dependent reactions?
Which of the following compounds is reduced during the light-dependent reactions?
What are the reactants required for photosynthesis?
What are the reactants required for photosynthesis?
What is the primary function of ATP synthase?
What is the primary function of ATP synthase?
What is the end result of the light-dependent reactions during photosynthesis?
What is the end result of the light-dependent reactions during photosynthesis?
Which step in the Calvin Cycle primarily utilizes CO2?
Which step in the Calvin Cycle primarily utilizes CO2?
How are G3P molecules related to glucose synthesis?
How are G3P molecules related to glucose synthesis?
What compound is reduced during the light reactions to form NADPH?
What compound is reduced during the light reactions to form NADPH?
What happens to the 5 G3P molecules produced after reduction?
What happens to the 5 G3P molecules produced after reduction?
Which of the following statements is true about light-independent reactions?
Which of the following statements is true about light-independent reactions?
What is the role of rubisco in the Calvin Cycle?
What is the role of rubisco in the Calvin Cycle?
What is the primary role of photosystem II (PSII) in the light-dependent reactions?
What is the primary role of photosystem II (PSII) in the light-dependent reactions?
What happens to the electron after it leaves the reaction center of PSII?
What happens to the electron after it leaves the reaction center of PSII?
What is the source of electrons that replaces the electron lost from PSII?
What is the source of electrons that replaces the electron lost from PSII?
In the context of photosynthesis, what is the purpose of the concentration gradient of H+ ions?
In the context of photosynthesis, what is the purpose of the concentration gradient of H+ ions?
What is the function of ATP synthase in the light-dependent reactions?
What is the function of ATP synthase in the light-dependent reactions?
What effect does the movement of energized electrons through the electron transport system have on H+ ions?
What effect does the movement of energized electrons through the electron transport system have on H+ ions?
Which term describes the process that links the movement of H+ ions to ATP production?
Which term describes the process that links the movement of H+ ions to ATP production?
What is produced as a byproduct during the breakdown of water molecules in photosynthesis?
What is produced as a byproduct during the breakdown of water molecules in photosynthesis?
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Study Notes
Photosynthesis Overview
- Photosynthesis is the process by which plants, algae, and some bacteria use sunlight to convert carbon dioxide and water into glucose and oxygen.
- The chemical equation for photosynthesis is: 6 CO2 + 6 H2O + light energy → 6 O2 + C6H12O6
- Photosynthesis takes place in chloroplasts, which are organelles found in plant cells.
- Photosynthesis consists of two sets of reactions: light-dependent reactions and light-independent reactions.
Light-Dependent Reactions
- Light-dependent reactions generate ATP and NADPH, which are used to power the light-independent reactions.
- Light-dependent reactions occur in the thylakoid membranes of chloroplasts.
- Light energy is absorbed by chlorophyll molecules in photosystems I and II (PSI and PSII).
- This energy excites electrons in chlorophyll, causing them to move to electron acceptors.
Photosystem II (PSII)
- PSII uses a process called chemiosmosis to produce ATP.
- When an electron leaves PSII, it creates an "electron hole".
- Water is split to replace the electron in PSII, releasing H+ ions, electrons, and oxygen gas (O2).
- The electrons from water move through an electron transport chain, losing energy along the way.
- The lost energy is used to pump H+ ions into the thylakoid space, generating a concentration gradient.
- H+ ions flow down the concentration gradient through ATP synthase, generating ATP from ADP and Pi.
Photosystem I (PSI)
- PSI also absorbs light energy, exciting electrons and passing them to an electron acceptor.
- The electrons from PSII replace those lost from PSI.
- The electrons from PSI are used to reduce NADP+ to NADPH.
Light-Independent Reactions (Calvin Cycle)
- The energy from ATP and NADPH is used in the light-independent reactions to synthesize glucose.
- Light-independent reactions occur in the stroma of chloroplasts.
- They consist of three main steps: carbon fixation, reduction, and regeneration of RuBP.
Carbon Fixation
- Carbon dioxide (CO2) combines with RuBP (ribulose bisphosphate) in the stroma, catalyzed by the enzyme rubisco.
- This creates an unstable 6-carbon compound that immediately breaks down into two 3-carbon compounds called 3-PGA (3-phosphoglycerate).
Reduction
- 3-PGA is converted to G3P (glyceraldehyde-3-phosphate) by using energy from ATP and NADPH.
- Two G3P molecules can combine to form one glucose molecule.
Regeneration of RuBP
- Five out of six G3P molecules are used to regenerate RuBP, requiring additional ATP.
- The Calvin cycle must repeat to produce one full glucose molecule.
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