Ciliate commonly used as experimental organism is

Options

A. Vorticella
B. Balantidium
C. Tetrahymena
D. Paramecium.

Answer

To answer the question "Ciliate commonly used as experimental organism is," we will follow these steps:

### Step 1: Identify the Ciliates
Ciliates are a group of protozoa characterized by the presence of cilia, which are short hair-like structures that aid in movement and feeding. The question provides a list of potential ciliates: Vorticella, Balantidium, Tetrahumana, Hymena, and Paramecium.

### Step 2: Understand the Role of Ciliates in Research
Ciliates are often used in experimental biology due to their unique characteristics and ease of manipulation in laboratory settings. They can serve as model organisms for studying various biological processes.

### Step 3: Evaluate Each Option
- **Vorticella**: A ciliate known for its stalked structure but not commonly used in experiments.
- **Balantidium**: A parasitic ciliate that causes disease in humans but is not typically used as a model organism.
- **Tetrahumana**: Known as Tetrahumana pyriformis, this ciliate is recognized for its utility in experiments and is the first protozoan cultivated axenically (in pure culture).
- **Hymena**: Not widely recognized as a model organism in research.
- **Paramecium**: A well-known ciliate used in experiments but not as commonly as Tetrahumana.

### Step 4: Conclusion
After evaluating the options, Tetrahumana (Tetrahumana pyriformis) is identified as the ciliate commonly used as an experimental organism due to its ability to be cultivated axenically and its controlled sexual life cycle.

### Final Answer
The ciliate commonly used as an experimental organism is **Tetrahumana**.

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