Single-unit smooth muscle fibres may contract automatically and rhythmically.

Answer

**Step-by-Step Solution:**

1. **Understanding Single-Unit Smooth Muscle:**
- Single-unit smooth muscle, also known as visceral smooth muscle, is a type of muscle found in various organs such as the uterus, gastrointestinal tract, and bladder.

2. **Characteristics of Single-Unit Smooth Muscle:**
- These muscle fibers are connected by gap junctions, allowing them to communicate and coordinate contractions.
- They are innervated by autonomic nerve fibers, meaning they are controlled involuntarily by the autonomic nervous system.

3. **Automatic and Rhythmic Contraction:**
- Single-unit smooth muscle fibers can contract automatically and rhythmically due to the presence of gap junctions. When one muscle cell contracts, the contraction can spread to adjacent cells.
- This property allows the muscle to respond to the needs of the organ it is part of, such as stretching and contracting in the gastrointestinal tract during digestion.

4. **Conclusion:**
- Based on the characteristics and functions of single-unit smooth muscle, the statement that "single-unit smooth muscle fibers may contract automatically and rhythmically" is indeed true.

**Final Answer:**
The statement is true.

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