The basic unit upon which the systems of classification are based is

Options

A. species
B. genus
C. order
D. family.

Explanation

To answer the question, "The basic unit upon which the systems of classification are based is," we will follow these steps:

### Step-by-Step Solution:

1. **Understanding Classification**:
- Classification in biology refers to the systematic arrangement of living organisms into categories based on shared characteristics. This process is known as taxonomy.

2. **Recognizing Taxonomic Ranks**:
- Taxonomic ranks are the levels of classification that help organize biological diversity. The main ranks include:
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species

3. **Identifying the Basic Unit**:
- Among these ranks, the species is considered the most fundamental unit. It represents a group of organisms that can interbreed and produce fertile offspring.

4. **Justifying the Choice of Species**:
- The species is the smallest taxonomic unit. It cannot be subdivided into smaller categories that still retain the ability to reproduce. Therefore, it serves as the basic unit of classification.

5. **Conclusion**:
- Based on the hierarchy of classification and the definition of species, the answer to the question is that the basic unit upon which the systems of classification are based is **species**.

### Final Answer:
The basic unit upon which the systems of classification are based is **species**.

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