In zinc deficiency, which leaves typically show chlorosis first?

• A. Oldest leaves
• B. Youngest leaves
• C. All leaves simultaneously
• D. Only petioles

Answer: (B)

Nutrient mobility inside the plant determines where deficiency symptoms appear. Zinc is relatively immobile, so it cannot be moved from older leaves to support new growth when zinc is lacking. The developing, youngest leaves are the first to show signs because they rely on zinc for chlorophyll production and other enzymes, and they cannot receive remobilized zinc from older tissues. That’s why chlorosis starts in the newest leaves rather than the oldest ones. The other patterns don’t fit zinc’s immobile nature, and chlorosis limited to petioles isn’t characteristic of this deficiency.