The table below lists potential environmental conditions in future climates, related to atmospheric carbon dioxide concentrations (CO2) and mean annual temperature (MAT). The table also lists potential outcomes with respect to whether conditions will favour grasses with C3 or C4 photosynthetic pathways. Assuming no other changes in environmental conditions, match the options in the two columns.
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Remember that C3 and C4 pathways are adapted to different environmental conditions. C3 plants are more CO2-responsive, while C4 plants handle high temperatures better.
Step 1: Understanding the Effects of Increased CO2 on C3 and C4 Plants.
C3 plants rely heavily on the Calvin cycle in photosynthesis, which is highly sensitive to the levels of CO2. In conditions where CO2 levels are elevated (condition P), C3 plants show improved efficiency and growth as they can more effectively convert CO2 into glucose. C4 plants, however, have a mechanism to efficiently capture CO2 even at lower concentrations, so increased CO2 does not benefit them as much as it does C3 plants.
Step 2: Understanding the Effects of Increased MAT on C3 and C4 Plants.
C4 plants possess a unique adaptation that allows them to thrive in high-temperature environments by minimizing photorespiration—a process that becomes prevalent and costly in C3 plants under hot conditions. When MAT (Mean Annual Temperature) increases (condition Q), C4 plants can perform photosynthesis more efficiently than C3 plants, which suffer from increased photorespiration.
Step 3: Matching the Outcomes to the Conditions.
- Increased CO2 benefits C3 plants more → Match P to (i)
- Increased MAT benefits C4 plants more → Match Q to (ii)
