Demyelination of axons in the peripheral nervous system leads to a loss of nerve conduction velocity. Scientists investigated whether transplanting neural crest stem cells could help repair demyelinated sciatic nerves in rats.
They divided rats with induced sciatic nerve demyelination into three groups:
After 14 days, the scientists measured the mean nerve conduction velocity of each group. The results are shown in the table below:
| Group | Mean nerve conduction velocity (m s−1\text{m s}^{-1}m s−1) |
|---|---|
| Control | 2.42.42.4 |
| TF-4+TF\text{-}4^+TF-4+ | 8.48.48.4 |
| TF-4−TF\text{-}4^-TF-4− | 4.84.84.8 |
Fourteen days after transplantation, histological analysis showed that in the TF-4+TF\text{-}4^+TF-4+ group, 65%65\%65% of the damaged nerve fibers were newly myelinated. The control group had no newly myelinated fibers.
Assuming that the increase in mean nerve conduction velocity above the control baseline is directly proportional to the percentage of damaged nerve fibers that are newly myelinated, calculate the percentage of damaged nerve fibers that are newly myelinated in the TF-4−TF\text{-}4^-TF-4− group.
21 exam-style questions on AQA A Level Biology Gene expression is controlled by a number of features (A-level only), covering Most of a cell's DNA is not translated (A-level only), Regulation of transcription and translation (A-level only), and Gene expression and cancer (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.