C₄ plants collect CO₂ in mesophyll cells, which are close to the leaf surface, then transfer it to bundle-sheath cells, which are rich in RuBP carboxylase and surround the “veins” that deliver water to the leaf tissue. C₃ plants carry out the entire Calvin cycle in mesophyll cells and have relatively fewer bundle-sheath cells. Explain why C₄ plants have an advantage over C₃ plants under drought conditions.