By looking at which internal structure of a plant you can tell whether a plant is C3 or C4? Explain.

The internal structure is the leaf’s cross-section showing Kranz anatomy, which is diagnostic of C₄ plants

• In Kranz anatomy, each vascular bundle is surrounded by two concentric layers of cells: an inner bundle sheath rich in chloroplasts and an outer ring of mesophyll cells
• The bundle sheath cells form a “wreath” (Kranz) around veins, concentrating CO₂ around Rubisco and minimizing photorespiration

C₃ plants lack Kranz anatomy; their mesophyll cells alone carry out both initial CO₂ fixation and the Calvin cycle without distinct bundle sheath specialization

Chloroplast characteristics differ:

In C₄ bundle sheath cells, chloroplasts often lack or have reduced grana stacks and are agranal or poorly granal to favor the Calvin cycle

Mesophyll chloroplasts in C₄ plants are granal, optimized for light reactions and initial CO₂ fixation by PEP carboxylase

Vein spacing and cell arrangement:

C₄ leaves exhibit higher vein density to facilitate efficient transport between mesophyll and bundle sheath cells

C₃ leaves have wider spacing between veins and no clear dual-cell‐type arrangement

Confirmation methods using internal anatomy:

Microscopic examination of leaf cross-sections stained to highlight cell walls and chloroplasts reveals the presence or absence of Kranz anatomy

Electron microscopy can further detail chloroplast ultrastructure (grana vs. agranal) in bundle sheath versus mesophyll cells