CAIE A-Level Biology A2 15.1.5 Action Potential Sequence Questions

Explain the sequence of an action potential using evidence from each question and mark scheme.

Exam points

Explain the sequence of an action potential.

[Maximum number: 6]

Humans detect the sweet taste of sucrose sugar using chemoreceptor cells in taste buds on the tongue. The red admiral butterfly, Vanessa atalanta, detects sucrose using chemoreceptor cells located on its antennae and on its tarsi (feet). The mode of action of the chemoreceptors in V. atalanta is similar to that in humans.

Fig. 10.1 shows the locations of the chemoreceptor cells on V. atalanta.

Fig. 10.1

Describe how the presence of sucrose causes an action potential in the sensory neurone associated with a chemoreceptor cell in V. atalanta.

any six from:
1 sucrose binds to, receptor protein / (chemoreceptor) cell surface receptor ;
2 ref. to second messenger ;
3 (chemoreceptor cell) $\mathrm{Na}^{+}$ entry / membrane depolarises ;
4 receptor / generator, potential ;
$5 \mathrm{Ca}^{2+}$ ions enter (chemoreceptor cell) ;
6 (named) neurotransmitter vesicles, move towards / fuse with, (presynaptic) membrane ;
7 (named) neurotransmitter, release / exocytosis, into (synaptic) cleft ;
8 (named) neurotransmitter binds to receptor on, sensory neurone / postsynaptic membrane ;
$9 \mathrm{Na}^{+}$ enters (through ligand-gated channel) → depolarisation ;
10 ref. to threshold for action potential ;
11 AVP ;

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CAIE A-Level Biology A2 15.1.5 Action Potential Sequence Questions question 1