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

Which of the following describes a reflex arc?

1. A circuit without receptors

2. Pathway involving a sensory neuron and an effector

3. A temporary response from the muscle only

4. A slow process involving only hormones

The correct answer is: Pathway involving a sensory neuron and an effector

The correct response accurately describes a reflex arc, which is a neural pathway that involves a sensory neuron and an effector. In a reflex arc, sensory neurons detect a stimulus and transmit this information to the central nervous system. From there, a response is quickly generated and sent to an effector, which is usually a muscle or gland, to produce an immediate reaction. This process allows for rapid responses to stimuli, helping to protect the body from harm, such as when pulling away from a hot surface. The other options do not encompass the full characteristics of a reflex arc. A reflex arc inherently includes receptors that detect stimuli, thereby making the description of a circuit without receptors incomplete. Furthermore, it is not limited to just temporary muscle responses, as it encompasses the entire pathway involving both sensory and motor neurons, including an immediate response to stimuli. Lastly, reflex arcs function through neural pathways rather than being slow and involving only hormonal processes, as they are designed for quick reflexive actions.