JIPMER2007BotanyPhotosynthesis in Higher Plants
Photosynthesis in C ₄ plants is relatively less limited by atmospheric CO ₂ levels because
Options
- Afour carbon acids are the primary initial CO ₂ fixation products
- Bthe primary fixation of CO ₂ is mediated via PEP carboxylase
- Ceffective pumping of CO ₂ into bundle sheath cells
- DRUBISCO in CO ₄ plants has higher affinity for CO ₂
Correct answer
B. the primary fixation of CO ₂ is mediated via PEP carboxylase
Step-by-step solution
The fixation of CO ₂ in C ₄ plants takes place in two places and by two different organic compounds. Phosphoenol pyruvate (PEP) is found in mesophyll cells which primarily fixes atmospheric CO ₂ into oxaloacetic acid (4C). RUBISCO is present in bundle sheath cells where final fixation of CO ₂ in hexose sugars takes place. CO ₂ is primarily fixed by PEP carboxylase because this enzyme has greater affinity to CO ₂ than RUBISCO.