What are essential elements? How many elements are reported from plants?

Explanation

### Step-by-Step Solution:

1. **Definition of Essential Elements**:
- Essential elements are those nutrients that a plant must have to complete its life cycle. Without these elements, the plant cannot grow, reproduce, or carry out its metabolic functions effectively.

2. **Characteristics of Essential Elements**:
- Essential elements have specific physiological roles in the plant's metabolism. They are involved in various biochemical processes that are crucial for the plant's health and development.
- These elements are irreplaceable, meaning that no other element can substitute for them in fulfilling their specific functions within the plant.
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