Model Answer
0 min readIntroduction
Photosynthesis, the cornerstone of life on Earth, varies significantly across plant species depending on their evolutionary adaptations. C3 photosynthesis, the most common pathway, was the initial mechanism. Later, C4 photosynthesis evolved as an adaptation to hot, arid environments. Understanding the differing responses of these pathways to environmental factors like temperature and CO2 concentration is crucial for comprehending plant physiology and agricultural strategies. The recent IPCC reports highlight the increasing environmental stresses impacting global agriculture, making this knowledge increasingly relevant.
Photosynthesis: A Comparative Overview
C3 photosynthesis, prevalent in plants like wheat, rice, and soybeans, involves the direct fixation of CO2 by RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase). C4 photosynthesis, found in plants like maize, sugarcane, and sorghum, initially fixes CO2 into a four-carbon compound via PEP carboxylase, bypassing RuBisCO initially.
Response to Temperature
Temperature significantly impacts photosynthetic rates by influencing enzyme activity. RuBisCO, the enzyme central to C3 photosynthesis, has a lower temperature optimum (around 25°C) and is also prone to oxygenation at higher temperatures, leading to photorespiration. PEP carboxylase, used in C4 plants, has a higher temperature optimum (around 35-40°C) and is less susceptible to photorespiration.
| Feature | C3 Plants | C4 Plants |
|---|---|---|
| RuBisCO Optimum Temperature | ~25°C | Not applicable (bypassed) |
| Photorespiration | High | Low |
| Temperature Sensitivity | More Sensitive | Less Sensitive |
Response to CO2 Concentration
C3 plants benefit significantly from increased CO2 concentrations as it enhances the carboxylation reaction by RuBisCO. However, their photosynthetic rate is limited by RuBisCO's efficiency. C4 plants, due to their initial CO2 fixation mechanism, maintain high CO2 concentration around RuBisCO, minimizing photorespiration even at lower ambient CO2 levels. This advantage diminishes as atmospheric CO2 levels rise.
The initial CO2 fixation in C4 plants involves two steps:
- PEP carboxylase fixes CO2 into oxaloacetate in mesophyll cells.
- Oxaloacetate is converted to malate, transported to bundle sheath cells, where it releases CO2, which is then fixed by RuBisCO.
Ecological Implications
C4 plants thrive in hot, dry environments with high light intensity because of their higher water use efficiency and reduced photorespiration. C3 plants are more dominant in cooler, wetter climates. Climate change, with increasing temperatures and altered CO2 levels, is influencing plant distribution and agricultural practices, potentially favoring C4 plants in some regions.
Case Study: Maize and Wheat in a Changing Climate
Maize (C4) and wheat (C3) are staple crops globally. As temperatures rise, maize generally exhibits better performance than wheat due to its higher temperature tolerance and lower photorespiration. However, with increasing CO2, the advantage of C4 plants might diminish, potentially impacting wheat yields in cooler regions. The Indian Council of Agricultural Research (ICAR) is actively researching drought-resistant varieties of both crops.
Scheme: National Mission for Sustainable Agriculture (NMSA)
The NMSA, launched in 2010 by the Indian government, promotes sustainable agricultural practices. A key component is developing climate-resilient crop varieties, including both C3 and C4 species, to mitigate the impacts of climate change on agricultural production. It focuses on improving water use efficiency and promoting drought-resistant varieties.
Conclusion
In conclusion, C3 and C4 plants exhibit distinct responses to temperature and CO2 concentration, driven by their differing photosynthetic pathways and enzymatic efficiencies. While C4 plants currently hold an advantage in warmer climates, rising CO2 levels may alter this dynamic. Understanding these physiological differences is vital for developing strategies to ensure food security in a changing climate and optimizing agricultural practices for various environments. Further research into improving RuBisCO efficiency in C3 plants remains a critical area of focus.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.