Which molecule(s) shuttle(s) between the mesophyll and bundle sheath cells in C₄ plants during carbon fixation? A) A four-carbon molecule only B) A three-carbon molecule only C) A two-carbon molecule only D) A four-carbon molecule and a three-carbon molecule E) Two different four-carbon molecules

Question

Quizplus · Accepted Answer

During carbon fixation in C₄ plants, a four-carbon molecule (usually malate or aspartate) is shuttled from mesophyll cells to bundle sheath cells where it is decarboxylated to release carbon dioxide. The released carbon dioxide is then fixed by Ribulose-bisphosphate carboxylase/oxygenase (Rubisco) using ATP and NADPH produced in the light reactions. The resulting three-carbon molecule (usually 3-phospho glycerate or glyceraldehyde-3-phosphate) is then transported back to mesophyll cells to regenerate the four-carbon molecule. Therefore, the molecule that shuttles between mesophyll and bundle sheath cells during carbon fixation are both four-carbon and three-carbon molecules. Choice D is the best answer.

Which Molecule(s) Shuttle(s) Between the Mesophyll and Bundle Sheath Cells