Which parts influence absorption of a herbicide on a leaf surface?

• A. The leaf surface parts, the cuticle and the stomates
• B. The xylem and phloem
• C. Chloroplasts
• D. The posterior leaf margin

Answer: (A)

Absorption across a leaf surface hinges on the outer entry points that control what gets in. The cuticle, a waxy protective layer covering the leaf, is the primary barrier a herbicide must penetrate. Its thickness, composition, and any disruptions or formulations designed to soften it strongly influence how easily a molecule can diffuse into the leaf.

The other important route is through stomata, tiny openings regulated by guard cells. When stomata are open, some herbicides can enter through these pores and move into the substomatal cavity and onward into internal tissues. So both the cuticle and stomata determine how much of the chemical actually gets inside.

In contrast, the xylem and phloem are internal transport systems that carry substances after absorption, not initial entry routes. Chloroplasts are organelles inside cells where photosynthesis happens, not portals for herbicide entry. The posterior leaf margin isn’t a dedicated absorption pathway; absorption is about crossing the surface barriers and entering through pores or cell walls, not about a specific leaf edge.