Multiple Choice
In which type of environment are plants most likely to use a C4 pathway of carbon fixation?
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9. Photosynthesis
C3, C4 & CAM Plants
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In C3 plants, the conservation of water promotes which of the following processes?
A
Increased photosynthetic efficiency
B
Enhanced carbon fixation
C
Photorespiration
D
Greater stomatal opening
Verified step by step guidance1
Understand the context: C3 plants are the most common type of plants that use the Calvin cycle for carbon fixation. They are called C3 because the first stable product of carbon fixation is a 3-carbon compound, 3-phosphoglycerate (3-PGA).
Recognize the trade-off: In C3 plants, stomata (pores on the leaf surface) regulate gas exchange. When stomata close to conserve water, less carbon dioxide (CO₂) enters the leaf, and oxygen (O₂) accumulates. This creates conditions that favor photorespiration.
Define photorespiration: Photorespiration is a process where the enzyme RuBisCO binds to O₂ instead of CO₂, leading to the production of a 2-carbon compound that is eventually recycled but results in energy loss and reduced photosynthetic efficiency.
Relate water conservation to photorespiration: When water is scarce, stomata close to prevent water loss. This reduces CO₂ availability and increases O₂ concentration inside the leaf, promoting photorespiration instead of efficient carbon fixation.
Conclude the relationship: The conservation of water in C3 plants indirectly promotes photorespiration because the conditions created by closed stomata (low CO₂ and high O₂) favor this less efficient process over normal photosynthesis.
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C3, C4 & CAM Plants practice set
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