Name three functional kingdoms of an ecosystem.

Explanation

To answer the question regarding the three functional kingdoms of an ecosystem, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Functional Kingdoms**:
- An ecosystem can be divided into different functional groups based on their roles in energy flow and nutrient cycling. The term "functional kingdoms" refers to these groups that actively contribute to the ecosystem's functioning.

2. **Identifying the First Kingdom - Producers**:
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