| Date | May 2010 | Marks available | 2 | Reference code | 10M.3.SL.TZ1.18 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 18 | Adapted from | N/A |
Question
Below is a diagram of a reflex arc for a pain withdrawal reflex.
Define reflex.
Label the parts indicated by the letters I–IV.
I. ..............................................................
II. ..............................................................
III. ..............................................................
IV. ..............................................................
Explain the role of parts I and II in a pain withdrawal reflex.
Markscheme
rapid response that occurs automatically/involuntarily in response to a stimulus
Two correct labels for [1]
I: sensory neuron
II: motor neuron
III: dorsal root (of spinal nerve) NOT dorsal root ganglion
IV: white matter (of spinal cord
receptor cell detects stimulus and converts it to a nerve impulse;
impulse travels along sensory neuron to (dorsal root of) spinal cord;
impulse travels along motor neuron to effector organ;
causes muscle to contract removing contact with painful stimulus;
Need to mention BOTH structures I AND II for 2 marks.
Examiners report
Many candidates could not give a correct definition of a reflex.
The labelling was also not well done.
There were many references to “signals” rather than “impulses” in the explanation, with often little connection to the parts shown in the diagram.
