Explain one-way transmission at the supplied chemical synapse
Use the releasing vesicles and receiving receptor arrangement.
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall cell membranes, diffusion, sensitivity and the difference between cells, tissues and organs.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which side contains the releasing vesicles here?
What you will learn
- Structure gives transmission a direction
- Follow the asymmetry of this junction
Explain one-way transmission at the supplied chemical synapse
| Feature | Meaning |
|---|---|
| Releasing side | Presynaptic vesicles contain transmitter |
| Receiving side | Postsynaptic receptor proteins bind it |
| Functional direction | First neurone towards next neurone |
| Explanation limit | Chemical connection supplied here; not all wider junction types |
Structure gives transmission a direction
Synapses ensure that impulses travel in one direction only in the required account. At the supplied chemical synapse, the arrangement of the two sides explains this direction. The first, presynaptic terminal contains vesicles holding neurotransmitter molecules for release; the next, postsynaptic membrane has the corresponding receiving receptor proteins.
An impulse arriving at the releasing terminal stimulates transmitter release into the gap. Molecules diffuse across and bind receptors on the next neurone, where an impulse is stimulated. The sequence therefore transfers information from the specified releasing cell to the specified receiving cell. A drawing arrow is a summary of this structural and mechanistic explanation, not the reason on its own.
Follow the asymmetry of this junction
Reversing the drawn arrow would not reverse the positions of vesicles and receiving receptors. In this supplied junction, the receiving side is not described as a second transmitter-releasing terminal directed back at the first side. Do not replace the required structural asymmetry with a claim that molecules cannot move randomly in the gap; diffusion and the functional direction of transmission are different ideas.
The statement applies to the chemical-synapse model taught here. It should not become an unsupported universal description of every electrical junction or every complex nervous circuit in wider biology. A circuit can contain multiple routes while each specified chemical synaptic connection has a releasing and receiving side. Use those sides to explain the one-way connection asked for in this syllabus requirement.
Pause and explain
Which explains the specified one-way connection?
Worked example
Explain the one-way direction in the supplied chemical junction.
Show the worked solution
- Vesicles release transmitter from the presynaptic side.
- Receiving receptor proteins are on the postsynaptic side.
Answer Transmission proceeds from the transmitter-releasing presynaptic terminal to the receptor-bearing postsynaptic neurone.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain why the supplied chemical synapse transmits in one direction.
Give me a hint
Use structures on both sides rather than only an arrow.
Compare my reasoning
- The presynaptic side has transmitter-containing release vesicles.
- The postsynaptic side has the corresponding receiving receptor proteins.
Transmitter is released from vesicles on the presynaptic side and binds receiving receptor proteins on the postsynaptic side, so the specified junction transmits from first neurone to next neurone.
Look for these in your work
- State releasing side
- State receiving side
A student reverses the arrow without changing the structures and says the junction now transmits backwards. Evaluate.
Give me a hint
A drawn arrow cannot relocate release and receiving machinery.
Compare my reasoning
- Vesicles remain on the presynaptic releasing side.
- Receptor proteins remain on the postsynaptic receiving side.
Changing the drawn arrow alone does not reverse the structure or transmission; the supplied vesicle and receptor arrangement still defines the original one-way connection.
Look for these in your work
- Use structural evidence
- Reject arrow-only causation
Random diffusion can move molecules in different microscopic directions. Does that erase the specified one-way synaptic transmission?
Give me a hint
Separate molecule motion from the functional receiving arrangement.
Compare my reasoning
- Diffusion occurs in the gap.
- Release and receiving receptors remain asymmetrically placed.
No. Molecular diffusion does not remove the releasing-versus-receiving arrangement; the supplied synaptic connection still transfers the signal towards the receptor-bearing next neurone.
Look for these in your work
- Distinguish motion and transmission
- Retain structural asymmetry
Common mistakes
- Saying the drawn arrow itself causes direction.
- Claiming random diffusion means normal signal transmission works equally both ways.
What can you explain now?
Which explains the specified one-way connection?
Compare with the explanation
Release on first side and receiving receptors on next side
The two sides have different roles.
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Make it stick
Explain one-way synaptic transmission using structures on both sides of the junction.
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