Why is that in certain plants deficiency symptoms appear first in younger parts of the plant while in others they do so in mature organs?

Explanation

### Step-by-Step Solution:

1. **Understanding Deficiency Symptoms**: Deficiency symptoms in plants occur when there is a lack of essential nutrients. These symptoms can manifest in different parts of the plant depending on the mobility of the nutrients involved.

2. **Mobility of Nutrients**: The key factor that determines where deficiency symptoms appear first is the mobility of the nutrients within the plant. Nutrients can be classified as either mobile or immobile:
- **Mobile Nutrients**: These nutrients can move easily throughout the plant. When there is a deficiency, the plant can relocate these nutrients from older tissues to support the growth of younger tissues.
- **Immobile Nutrients**: These nutrients cannot move easily within the plant. As a result, if there is a deficiency, the symptoms will appear in the younger parts of the plant because the older tissues retain the nutrients.

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