CAPF AC 2020 Q17: Science & Technology – Biology
- (a) cell body of nerve cell
- (b) nucleus of nerve cell
- (c) nerve endings of nerve cell
- (d) axon of nerve cell
Answer: (c) nerve endings of nerve cell
Explanation
How a nerve impulse crosses a synapse
How to think: follow the impulse through the neuron in order.
The chemical must be released at the last point, just before the gap.
| Step | Part of the nerve cell | What happens |
|---|---|---|
| 1 | Dendrite | Picks up the information |
| 2 | Cell body | The impulse passes through it |
| 3 | Axon | Carries the electrical impulse along its length |
| 4 | Nerve ending (end of the axon) | Releases chemicals |
| 5 | Synapse (the gap) | The chemicals cross it and start an impulse in the next neuron |
These chemicals are called neurotransmitters.
An example is acetylcholine.
Why (c) and not (d): the axon only conducts the impulse.
The chemicals come out at its tip, the nerve ending.
Answer: (c) nerve endings of nerve cell.
Why each option is right or wrong
- (a) Incorrect. The cell body holds the nucleus; it does not release the chemicals.
- (b) Incorrect. The nucleus controls the cell and takes no direct part in the synapse.
- (c) CORRECT. The nerve endings release the chemicals that cross the synapse.
- (d) Incorrect. The axon carries the electrical impulse; release happens only at its ending.
Key point
Impulse path: dendrite, cell body, axon, nerve ending. At the nerve ending the electrical impulse releases chemicals (neurotransmitters) that cross the synapse.
Remember
Electrical along the axon, chemical across the synapse, released at the nerve ending.
Common mistakes
- Choosing axon because the nerve ending is part of it; pick the most exact option.
- Thinking the impulse jumps the synapse as electricity; it crosses as a chemical.
- Reversing the direction: the impulse goes from dendrite to axon, not the other way.
Exam tip
When two options overlap, pick the more exact one. Nerve ending is more exact than axon.
Sources
- NCERT Class X Science — Control and Coordination (nervous system)
- NCERT Class XI Biology — Neural Control and Coordination