University of Central Florida (UCF) Biology Exit Practice Exam

C4 plants have adapted to thrive in conditions where photorespiration can reduce the efficiency of photosynthesis, particularly in hot and dry environments. The unique enzyme that plays a crucial role in minimizing this process is PEP carboxylase.

PEP carboxylase catalyzes the initial step in the C4 photosynthetic pathway by fixing carbon dioxide to phosphoenolpyruvate (PEP), resulting in the formation of oxaloacetate. This pathway allows C4 plants to capture carbon dioxide more effectively, even at lower concentrations, thus reducing the likelihood of photorespiration which occurs when the enzyme RuBisCO binds to oxygen instead of carbon dioxide. Since PEP carboxylase has a higher affinity for carbon dioxide than RuBisCO, it ensures that carbon dioxide is efficiently utilized and helps maintain higher levels of carbon fixation in the leaf cells.

This adaptation aids C4 plants in optimizing their photosynthetic efficiency under conditions where water loss is a concern, allowing them to open their stomata less and conserve water, thus benefiting their overall growth and productivity.