Questions and Answers
What do heterotrophic organisms primarily rely on to obtain energy?
What is the primary function of light-dependent reactions in photosynthesis?
Where does eukaryotic photosynthesis take place?
What is one of the main outputs of the light-independent reactions?
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Which type of photosynthesis produces oxygen as a byproduct?
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What distinguishes bacteriochlorophylls from chlorophylls?
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What role do pigments play in photosynthesis?
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What must happen to electrons lost from the reaction center during photosynthesis?
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Which compound is used as an electron donor in certain anoxygenic photosynthetic organisms?
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What happens during cyclic photophosphorylation?
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Where does the Calvin-Benson cycle occur in eukaryotic cells?
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Which enzyme is primarily responsible for adding CO2 to RuBP in the Calvin cycle?
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What is the primary function of the Calvin cycle?
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What are the two types of photosystems discovered by Joan Mary Anderson?
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In the Calvin cycle, what is G3P primarily used for?
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Which type of bacteria use only one photosystem for photosynthesis?
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Study Notes
Heterotrophic Organisms and Carbohydrates
- Heterotrophic organisms, including humans and E. coli, derive energy from carbohydrates.
- Carbohydrates are primarily produced through the process of photosynthesis.
Photosynthesis Overview
- Photosynthesis transforms sunlight into chemical energy, performed mainly by phototrophic organisms like plants and some microbes.
- Microbial photosynthesis is crucial for various ecosystems.
Stages of Photosynthesis
- Light-dependent reactions absorb sunlight through pigments, generating ATP and NADPH/NADH.
- Light-independent reactions utilize ATP and NADPH from the first stage to synthesize sugar molecules from CO2.
Main Outputs of Photosynthesis
- The primary products include ATP (energy carrier), NADPH/NADH (energy carriers), and sugars (organic energy forms).
Eukaryotic Photosynthesis
- Occurs in chloroplasts, which contain double membranes, thylakoids (organized in granum), and stroma (the surrounding fluid).
Prokaryotic Photosynthesis
- Takes place in thylakoids formed from infolded plasma membranes, with pigments in membranes converting light energy to chemical energy.
Photosystems
- Comprised of a light-harvesting complex and a reaction center that releases electrons upon absorbing energy.
Photosynthetic Pigments
- Different pigments absorb various light wavelengths, including:
- Bacteriochlorophylls (green, purple, red)
- Carotenoids (orange, red, yellow)
- Chlorophylls (green)
- Phycocyanins (blue)
- Phycoerythrins (red)
- Diverse pigments enhance light energy absorption.
Electron Transport System (ETS)
- High-energy electrons enter the ETS, resulting in the production of NADH or NADPH while ATP is generated through chemiosmosis.
Importance of Electrons in Photosynthesis
- Electrons released from the reaction center must be replenished for continuous photosynthesis.
Types of Photosynthesis
-
Oxygenic Photosynthesis:
- Found in plants and cyanobacteria.
- Uses water (H2O) as an electron source and produces oxygen (O2) as a byproduct.
-
Anoxygenic Photosynthesis:
- Conducted by some bacteria using compounds like hydrogen sulfide (H2S) or thiosulfate (S2O3²⁻).
- Does not produce oxygen but may generate elemental sulfur or sulfate ions.
Discovery of Photosystems
- Joan Mary Anderson identified two photosystems: Photosystem I (PSI) and Photosystem II (PSII).
- Different parts of chloroplasts yield distinct products; both photosystems are present in cyanobacteria and plant chloroplasts, while anoxygenic bacteria utilize only one.
Energy Production Mechanisms
- Noncyclic photophosphorylation generates both ATP and NADPH when required:
- Electrons flow from PSII to PSI via ETS, with water splitting replenishing electrons at PSII.
- PSI reduces NADP+ to form NADPH in the Z-scheme.
- Cyclic photophosphorylation is employed when ATP needs exceed NADPH needs, utilizing only PSI with electrons returning to PSI.
Light-Independent Reactions (Calvin Cycle)
- Converts CO2 into carbohydrates for energy storage, relying on ATP and NADPH from photosynthesis.
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Calvin-Benson Cycle Stages:
- Fixation: RuBisCO enzyme adds CO2 to RuBP, forming 3-PGA.
- Reduction: 6 ATP and 6 NADPH convert 3-PGA into G3P, used to create glucose.
- Regeneration: Remaining G3P regenerates RuBP using 3 ATP, continuing the cycle.
Additional Insights
- RuBisCO is the most abundant enzyme on Earth, making up 30%-50% of soluble proteins in plant chloroplasts.
- The Calvin cycle is utilized by plants, photoautotrophic bacteria, and some non-photosynthetic chemoautotrophs.
- Other microorganisms may employ different systems for CO2 fixation.
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Description
This quiz explores the vital processes of photosynthesis and the role of heterotrophic organisms like E.coli and humans in energy acquisition. Learn about the two main stages of photosynthesis and the importance of phototrophic organisms in ecosystems. Test your knowledge on how sunlight is converted into chemical energy.
