Neco 2025 Biology Question 44

Practice objective / multiple choice question 44 from the 2025 Neco Biology examination.

Neco 2025 Biology Objective / Multiple Choice Medium Difficulty
Question 44 NECO • 2025 • BIOLOGY • objective
Neco 2025 Biology Question 44 diagram

A neurotoxin blocks voltage‑gated Ca\(^{2+}\) channels at the presynaptic terminal of the neuromuscular junction. (a) Outline the normal sequence of events from arrival of an action potential in the motor neuron to contraction of the skeletal muscle fibre. (b) Indicate which step is directly inhibited by the toxin. (c) Predict the observable effect on a voluntary hand‑grip test.

Answer Options

A. The toxin inhibits the reuptake of acetylcholine in the synaptic cleft, causing prolonged muscle contraction; the hand‑grip test shows sustained force (tetany).
B. The toxin blocks the Ca\\(^{2+}\\) influx step, but acetylcholine release still occurs; consequently the hand‑grip test shows normal force with a slight delay (delayed contraction).
Correct Answer C. The toxin blocks the Ca\(^{2+}\) influx step, preventing acetylcholine release; as a result the hand‑grip test shows little or no force (muscle paralysis).
D. The toxin blocks the Na\\(^{+}\\) influx step, preventing depolarization of the muscle membrane; as a result the hand‑grip test shows reduced but detectable force (partial weakness).
Correct Answer
C
Correct Option:
The toxin blocks the Ca\(^{2+}\) influx step, preventing acetylcholine release; as a result the hand‑grip test shows little or no force (muscle paralysis).

About This Question

This is Neco 2025 Biology Question 44. It is one of the objective questions from the 2025 Neco Biology examination.

Difficulty level: Medium .

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