WAEC Biology 2017 Papers

Concept:A reflex arc carries an impulse in one fixed direction, from the receptor to the effector, through a chain of neurons connected by synapses.Explanation:A receptor first detects the stimulus and sends an impulse along a sensory neuron.At the first synapse, the impulse is passed to an intermediate neuron.At the second synapse, the impulse is passed from the intermediate neuron to a motor neuron.The motor neuron then carries the impulse to the effector, which brings about the response.Therefore, the correct order is receptor $\rightarrow$ sensory neuron $\rightarrow$ synapse $\rightarrow$ intermediate neuron $\rightarrow$ synapse $\rightarrow$ motor neuron $\rightarrow$ effector.Answer:A. $\text{Receptor} \rightarrow \text{sensory neuron} \rightarrow \text{synapse} \rightarrow \text{intermediate neuron} \rightarrow \text{synapse} \rightarrow \text{motor neuron} \rightarrow \text{effector}$