Helical contractile sheach occurs in

Options

A. Bacteria
B. Bacteriophage
C. Riboviruses
D. Fungi

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the occurrence of a "helical contractile sheath." This is a specific structure related to certain microorganisms.

2. **Analyzing the Options**: The options provided are:
- A) Bacteria
- B) Bacteriophage
- C) Riboviruses
- D) Fungi

3. **Identifying the Correct Structure**: The helical contractile sheath is a feature associated with certain types of viruses, particularly bacteriophages.

4. **Focusing on Bacteriophages**: Bacteriophages, such as the T4 bacteriophage, have a structure that includes a helical contractile sheath. This sheath surrounds the tail of the bacteriophage and is involved in the process of injecting genetic material into the host bacteria.

5. **Conclusion**: Based on the analysis, the helical contractile sheath occurs in bacteriophages. Therefore, the correct answer is option B) Bacteriophage.

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