A Level Biology Practice Exam

What distinguishes smooth muscle from other types of muscle?

1. It has striations visible under a microscope

2. It contracts without the need for conscious thought

3. It is primarily found in the heart

4. It enables voluntary movements

The correct answer is: It contracts without the need for conscious thought

Smooth muscle is distinguished from other types of muscle by its ability to contract without requiring conscious thought. This characteristic is crucial because smooth muscle plays a significant role in involuntary movements in various organs, such as the digestive tract, blood vessels, and respiratory system. These contractions help regulate functions like peristalsis in the intestines or the diameter of blood vessels. In contrast, striated muscles, which include both skeletal and cardiac muscle, are characterized by their striated appearance under a microscope, whereas smooth muscle lacks these striations. Additionally, smooth muscle is not primarily found in the heart; cardiac muscle serves that function. Lastly, smooth muscle operates involuntarily, in contrast to skeletal muscle, which facilitates voluntary movements.