IB Biology HL 2.2.4 Speed of impulse transmission Question Bank
Practise IB Biology HL 2.2.4 by analysing conduction-velocity data and explaining differences between axons.
- Syllabus
- First assessment 2025
- Course
- Biology HL
- Level
- HL
Exam points
- Calculate and compare conduction velocities from experimental nerve-data.
- Evaluate how myelination and axon structure explain differences in transmission rate.
C2.2.4—Variation in impulse speed question 1
Earthworms (Lumbricus terrestris) have a nerve cord on the ventral (underside) side of their body. It contains three nerve fibres (axons), each with a very large diameter, which extend along the whole length of the nerve cord. There is one medial giant fibre (MGF) and two lateral giant fibres (LGFs). The diameter of the MGF is 1.4 times larger than the LGF.
Scientists developed a non-invasive method to record giant nerve fibre activity. The response from the MGF was measured by the electrical activity produced when touching the front segments of the earthworm while the LGF was measured when touching the back segments.
The table shows the mean conduction rates, standard deviation (SD) and number of individual measurements of MGF and LGF action potentials in each earthworm. At the end of the table, the mean and standard error (SE) for 9 of the earthworms are shown.
Question (a)
(a)
Calculate how many times faster the mean MGF is compared to the mean LGF.
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Question (b)
(b)
Suggest one possible reason that the conduction rate in the MGF is much faster than in the LGF.
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