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Questions and Answers
What is the primary role of chlorophyll a in photosynthesis?
How do accessory pigments enhance photosynthesis?
What happens to the electrons in chlorophyll during the light-dependent reactions?
What is produced as a byproduct of water splitting during photosynthesis?
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Where do the light-dependent reactions of photosynthesis occur?
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What is the primary role of the reaction center in the photosystem?
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Which pigment is responsible for the coloration in the thylakoid membranes other than chlorophyll a?
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How does ATP synthase contribute to the light-dependent reactions?
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What is the initial step in the Calvin cycle?
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What role does the enzyme RuBisCO play in the Calvin cycle?
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What happens to the electrons that are donated from photosystem II (PSII)?
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During the splitting of water in photosystem II (PSII), which substances are produced?
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Which of the following statements about light-independent reactions is true?
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Study Notes
Light and Pigments
- Pigments absorb light in the visible spectrum.
- Violet/Blue light has shorter wavelengths and higher energy.
- Red light has longer wavelengths and lower energy.
- Plants use chlorophyll a, chlorophyll b, carotenoids, and xanthophylls.
- Pigments absorb a wide range of wavelengths.
- They convert light energy into chemical energy.
Structures
- Chlorophyll a absorbs blue-violet light and reflects blue-green.
- Chlorophyll b absorbs red-blue light and reflects yellow-green.
- Carotenoids absorb blue-purple light and reflect orange.
- Xanthophylls absorb blue-purple light and reflect yellow.
- Accessory pigments absorb other colors of light that chlorophyll a cannot.
- They help boost energy absorption.
Photosystems
- Photosystems contain pigment molecules (chlorophyll) and proteins.
- They are located in the thylakoid membranes.
- Photosystems absorb photons.
- They excite electrons in chlorophyll, causing the chlorophyll to donate these electrons.
- Water is split to replace the two electrons.
- Chlorophyll is regenerated.
- Oxygen is released to the environment, and hydrogen ions are transported to the thylakoid space.
Electron Transport
- Photosystem I (P700) and Photosystem II (P680) are involved in electron transport.
- Electrons are passed along electron acceptors.
- The final electron acceptor is NADP+, which is reduced to NADPH.
- ATP synthase is involved in the process.
Light-Dependent Reactions
- Light-dependent reactions require sunlight.
- Energy from sunlight is absorbed by chlorophyll and converted into stored chemical energy in the form of NADPH and ATP.
- They occur in the thylakoid membranes within the chloroplast.
- The reaction center contains chlorophyll a.
- Energy is transferred to the primary electron acceptor.
- Antenna pigments include chlorophyll b, carotenoids, and xanthophylls.
Electron Flow
- PSII transfers electrons to proteins in the membrane, initiating the electron transport chain (ETC).
- Electron energy moves hydrogen ions from the stroma to the thylakoid space.
- After energy is used, the electrons are accepted by a pigment molecule in PSI.
- The electrochemical gradient created by the movement of hydrogen ions creates a charge.
- Hydrogen ions move down the gradient through ATP synthase.
Water Splitting
- To replace the electrons in the reaction center, a water molecule is split.
- This releases an electron and results in the formation of oxygen and hydrogen ions in the thylakoid space.
- Oxygen molecules are released to the environment.
- Hydrogen ions play a critical role in the light-dependent reactions.
Calvin Cycle
- The Calvin cycle is light-independent.
- It is also known as the dark reaction.
- Carbon dioxide enters through stomata and diffuses into the stroma.
- It uses energy from the light reactions (ATP and NADPH).
Light-Independent Reactions
- The light-independent reactions or Calvin cycle use energized electrons from the light-dependent reactions to form carbohydrates from carbon dioxide.
- They do not require light directly.
- They depend on ATP and NADPH to drive the construction of new carbohydrate molecules.
- After energy transfer, the energy carrier molecules return to the light-dependent reactions.
Calvin Cycle Steps
- The Calvin cycle consists of fixation, reduction, and regeneration.
- The enzyme RuBisCO is involved.
- The molecule ribulose bisphosphate (RuBP) is crucial.
Photosystems (Summary)
- Two types of photosystems are embedded in the thylakoid membrane: PSII and PSI.
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Description
This quiz explores the role of pigments in photosynthesis, detailing how different pigments absorb and reflect light. Understand the structures of chlorophyll a, chlorophyll b, carotenoids, and xanthophylls, along with their functions in photosystems. Test your knowledge on how plants convert light energy into chemical energy.
