Questions and Answers
Which pigment is primarily responsible for photosynthesis in plants?
What color of light shows maximum absorption by chlorophyll a?
What can be inferred about the relationship between absorption by chlorophyll a and the rate of photosynthesis?
Which of the following pigments appears yellow-green in chromatography?
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How many different pigments contribute to the color seen in leaves?
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What is the primary product of cyclic photophosphorylation when only PS I is functional?
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Where does cyclic photophosphorylation primarily occur in the chloroplast?
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What happens to the excited electron during cyclic photophosphorylation?
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Which of the following conditions promotes cyclic photophosphorylation?
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What is synthesized alongside NADPH + H+ through the conventional electron transport chain involving both photosystems?
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Study Notes
Leaf Pigments and Photosynthesis
- Leaf pigments are separated using paper chromatography, revealing four main pigments: Chlorophyll a (bright blue-green), Chlorophyll b (yellow-green), xanthophylls (yellow), and carotenoids (yellow to yellow-orange).
- Pigments absorb specific wavelengths of light, essential for photosynthesis, with chlorophyll a being the most abundant pigment in plants.
- Chlorophyll a shows maximum absorption in the blue and red light regions, correlating with the highest rates of photosynthesis.
Electron Transport and Photophosphorylation
- Two photosystems (PS I and PS II) are connected through an electron transport chain, facilitating the synthesis of ATP and NADPH during photosynthesis.
- In cyclic photophosphorylation, when only PS I functions, electrons are recycled within the photosystem to generate ATP without producing NADPH.
- This process occurs when light wavelengths exceed 680 nm.
C4 Photosynthesis Pathway
- The C4 pathway begins with the formation of OAA (oxaloacetic acid) in the mesophyll cells, which is converted into malic or aspartic acid and then transported to bundle sheath cells.
- In bundle sheath cells, C4 acids release CO2, entering the Calvin cycle, while the 3-carbon molecule returns to mesophyll to regenerate PEP (phosphoenolpyruvate).
- The Calvin pathway, common to all plants, operates differently in C3 and C4 plants—C3 plants carry it out in mesophyll cells, while C4 plants do it in bundle sheath cells.
Photorespiration
- Photorespiration occurs in C3 plants, resulting from RuBisCO binding to O2 instead of CO2, leading to reduced CO2 fixation and no production of sugars or ATP.
- RuBisCO, an abundant enzyme, has an active site that can bind either CO2 or O2, with its affinity for CO2 being higher when their concentrations are balanced.
- C4 plants avoid photorespiration by increasing intracellular CO2 concentration, enhancing RuBisCO's carboxylase activity.
Comparisons and Productivity
- C4 plants exhibit higher productivity and yield due to their efficient CO2 fixation process and ability to tolerate higher temperatures compared to C3 plants.
- ATP synthesis in chloroplasts relies on the breakdown of proton gradients facilitated by the F0 portion of the ATPase enzyme, and water splitting associated with PS II releases oxygen and protons.
Summary of Key Processes
- Light reactions: Splitting of water, generating ATP/NADPH.
- Calvin cycle: CO2 fixation by RuBisCO to form 3PGA, which is converted to sugar, utilizing ATP and NADPH from light reactions.
- In C4 plants, CO2 fixation occurs in the mesophyll, while the Calvin cycle mode is in the bundle sheath, optimizing photosynthesis under varying conditions.
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Description
Explore the fascinating world of plant pigments through this quiz on paper chromatography. Discover the different pigments that contribute to the colors we see in leaves, including chlorophyll a, chlorophyll b, xanthophylls, and carotenoids. Test your understanding of their roles in photosynthesis!
