_______ helps in regulating buoyancy in water

Explanation

**Step-by-Step Solution:**

1. **Understanding Buoyancy**: Buoyancy refers to the ability of an organism to float or remain suspended in water. This is crucial for aquatic organisms, including certain bacteria, as it allows them to access light and nutrients effectively.

2. **Identifying Structures that Aid Buoyancy**: In bacteria, specific structures are responsible for regulating buoyancy. These structures need to be air-filled to provide the necessary lift in water.

3. **Gas Vacuoles**: The primary structure that helps in regulating buoyancy in aquatic bacteria is known as gas vacuoles. These are cylindrical, air-filled structures that can adjust the buoyancy of the bacteria by changing their volume.

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