OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What type of movement occurs when muscles only pull?

1. Contraction

2. Relaxation

3. Extension

4. Flexion

The correct answer is: Contraction

Muscle movement is primarily based on the principle that muscles can only contract or pull; they cannot push. When a muscle contracts, it shortens and pulls on the bone it is attached to, resulting in movement at a joint. Therefore, the type of movement that occurs when muscles are actively engaged is contraction. This is essential for various bodily movements, such as lifting, walking, or any activity involving muscle engagement. The other terms refer to different aspects of muscle and joint movement. Relaxation describes the state when a muscle is not contracting, allowing it to lengthen and return to its resting state. Extension and flexion are specific types of movements around a joint. Flexion reduces the angle between two body parts (like bending the elbow), while extension increases the angle (like straightening the elbow). Both involve a combination of the contraction and relaxation of muscles but do not define the fundamental principle that muscles can only pull. Thus, contraction is the answer that best describes the nature of muscle movement.