Which leaves have thinner cuticles?

• A. Mature sun leaves have thinner cuticles.
• B. Shaded and younger leaves/plants have thinner cuticles.
• C. All leaves have the same cuticle thickness.
• D. Leaves in high humidity have thinner cuticles.

Answer: (B)

Leaf cuticle thickness changes with light exposure and leaf age. Sun-exposed, mature leaves face greater risk of water loss and sun damage, so they develop a thicker cuticle to protect the tissue. In contrast, shaded environments reduce transpiration demand, and younger leaves are still developing their protective layers, so their cuticles are thinner. That’s why shaded and younger leaves have thinner cuticles. Humidity affects water loss mainly through stomatal behavior rather than thinning the cuticle itself, so it isn’t a reliable predictor of cuticle thickness.