The basic unit of biological classification is a species.

Answer

### Step-by-Step Solution:

1. **Understanding Biological Classification**:
- Biological classification is the system used to categorize and organize living organisms into groups based on shared characteristics.

2. **Defining Species**:
- A species is defined as a group of organisms that can interbreed and produce fertile offspring. It is the most specific level of classification in the taxonomic hierarchy.

3. **Taxonomic Rank**:
- In the taxonomic hierarchy, species is one of the ranks. The hierarchy typically includes domains, kingdoms, phyla, classes, orders, families, genera, and species, with species being the most specific rank.

4. **Role of Species in Biodiversity**:
- Species are fundamental units of biodiversity. They represent the variety of life forms on Earth, and understanding species helps in studying ecosystems and conservation efforts.

5. **Conclusion**:
- The statement "The basic unit of biological classification is a species" is true. It emphasizes the importance of species in both classification and biodiversity.