| Cross-sections of leaves from C3 (left) and
C4 plants. Note the differences in bundle sheath cells
(highlighted). In C3 plants, bundle sheath cells do not contain
chloroplasts; carbon fixation and Calvin Cycle reactions occur in
mesophyll cells (and in the presence of oxygen). In C4 plants,
the bundle sheath cells contain chloroplasts; carbon is fixed in
mesophyll cells, then transported to bundle sheath cells where Calvin
Cycle reactions occur in the absence of oxygen. In both, photosynthesized
sugars then enter the plant's vascular system. |
