Deficiency of mobile elements first appear on:

Options

A. older leaves
B. Apical meristems
C. Younger leaves
D. Flower petals

Answer

**Step-by-Step Solution:**

1. **Understanding Mobile Elements**: Mobile elements in plants are nutrients that can move from one part of the plant to another. This means that if there is a deficiency of these nutrients, the plant can redistribute them from older tissues to newer tissues.

2. **Identifying the Location of Deficiency**: When a mobile element is deficient, the plant will first draw from older leaves to supply the younger leaves and growing tissues. Therefore, the deficiency symptoms will first appear in the older leaves.

3. **Analyzing the Options**:
- **Older Leaves**: This is where the deficiency of mobile elements will first appear, as nutrients are moved to support growth in younger leaves.
- **Apical Meristem**: This is a growing region, but it will not show deficiency first as it receives nutrients from older parts.
- **Younger Leaves**: These leaves will not show deficiency first because they receive nutrients from older leaves.
- **Flower Petals**: These are not the first to show deficiency as they are not the primary growth sites.

4. **Conclusion**: Therefore, the correct answer is that the deficiency of mobile elements first appears in the older leaves.

**Final Answer**: Older leaves.

---