Final answer:
Mesophyll cells in C4 plants fix carbon into a four-carbon compound that is transported to bundle sheath cells, not exported directly, hence the answer to whether mesophyll cells export their 4-carbon products is 2) No.
Step-by-step explanation:
The mesophyll cells of a leaf play a crucial role in the fixation and storage of carbon. In C4 plants, an enzyme called PEP carboxylase enables mesophyll cells to bind carbon dioxide to a three-carbon compound (PEP) forming a four-carbon compound. This four-carbon compound is then transported through plasmodesmata to the bundle sheath cells where it undergoes decarboxylation releasing carbon dioxide for the Calvin cycle.
So, in the case of C4 plants, mesophyll cells do not directly export their 4-carbon products for use elsewhere, but rather pass them on to adjacent bundle sheath cells, where CO2 is then released and used in photosynthesis. Therefore, the correct answer to whether mesophyll cells export their 4-carbon products is No.
Furthermore, it's worth noting that in CAM plants, the strategy differs with a temporal separation of carbon fixation, but similarly, the four-carbon compounds are refixed to release CO2 during the day, illustrating that direct export of these compounds is not the primary function in these cells.