What are the symptoms of a phosphorus deficient plant? Where do these symptoms first appear in the plant?

Explanation

### Step-by-Step Solution:

1. **Understanding Phosphorus Role in Plants**:
- Phosphorus is an essential nutrient for plants, playing a critical role in energy transfer, photosynthesis, and the synthesis of nucleic acids and proteins.

2. **Identifying Symptoms of Phosphorus Deficiency**:
- The first noticeable symptom of phosphorus deficiency is that the leaves and stems of the plant turn dark green.
- The older leaves are typically affected first, which may develop a purplish discoloration.
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