Question 18M.3.HL.TZ2.7c
| Date | May 2018 | Marks available | [Maximum mark: 2] | Reference code | 18M.3.HL.TZ2.7c |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | c | Adapted from | N/A |
An organism’s diminished response to a repeated stimulus is referred to as habituation. The diagrams show the experiments performed on habituation to a stimulus in a sea slug (Aplysia californica). The sea slug is a mollusc that has an external gill for gas exchange. If the siphon of the sea slug is stimulated mechanically, it withdraws the gill in a simple reflex action.
With reference to the withdrawal of the siphon in Aplysia californica, explain the concept of summation.
[2]
a. summation is the sum of all depolarization impulses/neurotransmitters released in the synapse/synaptic cleft of the effector/motor neuron
b. in control more excitatory than inhibitory so effect would be excitatory
c. less of each in habituated so not enough to produce action potential in the effector/motor neuron
