Final answer:
The product that exits mesophyll cells via plasmodesmata and enters bundle sheath cells in C4 photosynthesis is malic acid. It is converted to pyruvate and carbon dioxide, released during this process, is fixed by Rubisco in the Calvin cycle. This system allows for more efficient water use and faster carbon fixation in C4 plants.
Step-by-step explanation:
In C4 photosynthesis, the product that exits the mesophyll cells via plasmodesmata and enters the bundle sheath cells is malic acid. It is rapidly transferred from the mesophyll to the bundle sheath cells, where it is converted to pyruvate. The carbon dioxide released during this process is fixed by Rubisco in the Calvin cycle. The remaining three-carbon fragment is transported back to the mesophyll cells. This system allows for more efficient water use and faster carbon fixation in C4 plants.