Protozoans are classified on the basis of

Options

A. Nutrition
B. Reproduction
C. Mode of locomotion
D. Excretion

Answer

### Step-by-Step Solution

1. **Understanding Protozoans**: Protozoans are single-celled organisms that belong to the kingdom Protista. They are diverse and can be found in various environments.

2. **Criteria for Classification**: Protozoans can be classified based on several criteria, including:
- Nutrition
- Reproduction
- Mode of locomotion
- Excretion

3. **Nutrition**: Most protozoans are holozoic, meaning they cannot produce their own food (they are not autotrophic) and rely on other organisms for nutrients. This aspect is one of the criteria for classification but is not the primary basis.

4. **Reproduction**: Protozoans reproduce through two main methods:
- Asexual reproduction (e.g., binary fission)
- Sexual reproduction (e.g., syngamy or conjugation)
While reproduction is an important characteristic, it is not the main basis for classification.

5. **Mode of Locomotion**: This is a significant criterion for classifying protozoans. There are three main types of locomotion:
- **Ciliary Movement**: Involves cilia, which are hair-like structures that help in movement.
- **Flagellar Movement**: Involves one or two long, whip-like structures called flagella that enable wave-like movement.
- **Amoeboid Movement**: Involves the use of pseudopodia, which are extensions of the cell that help in movement and food capture.

6. **Excretion**: Protozoans primarily excrete waste through contractile vacuoles, which expel excess water and waste products. While this is an important function, it is not a primary basis for classification.

7. **Conclusion**: The primary basis for classifying protozoans is their mode of locomotion, as it distinguishes them into different groups based on how they move.

### Final Answer
Protozoans are classified primarily on the basis of their mode of locomotion.

---