# Explain how the structure of a chemical synapse ensures that neural signals are transmitted in one direction only.

> IB DP Biology Standard Level (2023 syllabus) — C2.2 Neural signalling · Explain · 4 marks

## Mark scheme (4 marks)

1. Synaptic vesicles containing neurotransmitter are located only in the presynaptic terminal / presynaptic knob
2. Receptor proteins / ligand-gated ion channels for the neurotransmitter are located only on the postsynaptic membrane
3. Neurotransmitter diffuses across the synaptic cleft and binds to postsynaptic receptors, generating a signal in the postsynaptic neuron
4. The presynaptic membrane lacks receptors, so the postsynaptic neuron cannot trigger a signal in the presynaptic neuron / signal cannot travel in reverse

## Key terms

- [chemical synapse](https://www.gradenine.co.uk/glossary/chemical-synapse)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-a-b31e1258) · Published by Druglandscape Ltd.