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

What happens to transmitter substances after crossing the synapse?

1. They get destroyed

2. They become reabsorbed by the neuron

3. They diffuse back into the synapse

4. They are converted into energy

The correct answer is: They become reabsorbed by the neuron

Transmitter substances, also known as neurotransmitters, play a crucial role in the communication between neurons. After they are released into the synaptic cleft (the space between two neurons), they bind to receptors on the post-synaptic neuron, leading to the continuation of the nerve impulse. The reabsorption of neurotransmitters by the pre-synaptic neuron is a common process known as reuptake. This mechanism helps to clear neurotransmitters from the synapse after they have fulfilled their function in transmitting the signal. By being reabsorbed, the neurotransmitters can be repackaged into vesicles and used again in future synaptic transmissions. This recycling is important for maintaining the balance of neurotransmitters and ensuring efficient neuronal signaling. In contrast, other options describe processes that either don't accurately represent what occurs to neurotransmitters after synaptic transmission or do not align with known biological mechanisms. For example, while neurotransmitters can be destroyed by enzymes, this is not the primary process that occurs immediately after crossing the synapse. Additionally, the idea that neurotransmitters diffuse back into the synapse or are converted into energy does not reflect the accurate biochemical pathways involved in synaptic communication.