A-LevelBiologyControl and coordination9700/43 · May/June 2023 · Q98 Marks

(a) Dopamine is a neurotransmitter released in some synapses in the brain. The release and action of dopamine is similar to that of acetylcholine. Fig. 9.1 is a diagram of a brain synapse where dopamine is the neurotransmitter. dopamine vesicle presynaptic membrane iir postsynaptic membrane Fig. 9.1

(a)(i)Describe how the release of dopamine from the presynaptic neurone can lead to an action potential in the postsynaptic neurone.[4]
(a)(ii)In brain cells, the amino acid tyrosine is changed into DOPA, which then is converted to dopamine. Name another compound in the body produced from DOPA.[1]
(b)In some brain synapses, the neurotransmitter gamma-aminobutyric acid (GABA) is released. This results in an influx of chloride ions into the postsynaptic neurone. Suggest and explain whether an action potential would be generated in the postsynaptic neurone if GABA is released into a brain synapse.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

any four from:
[1] (dopamine) diffuses across synaptic cleft ;
[1] binds to receptors ;
[1] on postsynaptic membrane ;
[1] Na+ channels open R voltage gated channels or influx of Na+ into post synaptic neurone ;
[1] depolarisation of postsynaptic membrane ;
[1] ref. threshold ;
[1] dopaquinone ; A melanin
any three from:
[1] Cl- influx makes (inside of postsynaptic neurone) more negative / stays negative ;
[1] hyperpolarisation / remains polarised ;
[1] (not enough Na⁺ enter so) less likely to reach threshold ;
[1] no depolarisation of (postsynaptic) membrane ;
[1] (so) no action potential ;

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.