AQA AS Level CHEMISTRY Paper 2
Organic and Physical Chemistry JUNE
2025 Mark Scheme
Question 1
Serotonin (5-HT) is primarily synthesized in which brain structure?
A. Locus coeruleus
B. Substantia nigra
C. Raphe nuclei
D. Nucleus accumbens
Correct Answer: C
Rationale: Serotonin is synthesized in the raphe nuclei of the brainstem. The locus coeruleus produces
norepinephrine, the substantia nigra produces dopamine, and the nucleus accumbens is part of the
reward pathway involved in dopamine transmission.
Question 2
Which neurotransmitter is primarily associated with the "fight or flight" response and is the target of
beta-blockers?
A. Acetylcholine
B. Dopamine
C. Norepinephrine
D. GABA
Correct Answer: C
Rationale: Norepinephrine mediates the sympathetic "fight or flight" response. Beta-blockers (e.g.,
propranolol) block norepinephrine receptors, reducing heart rate, blood pressure, and physical anxiety
symptoms.
Question 3
A patient experiencing EPS from antipsychotic medication is given benztropine (Cogentin). Which
neurotransmitter system is primarily affected by this treatment?
A. Serotonin
B. Dopamine
C. Acetylcholine
D. Glutamate
,Correct Answer: C
Rationale: Benztropine is an anticholinergic medication that blocks acetylcholine receptors. By reducing
acetylcholine activity, it helps restore the balance between dopamine and acetylcholine in the basal
ganglia, alleviating EPS symptoms.
Question 4
The mechanism of action of SSRIs involves:
A. Blocking norepinephrine reuptake only
B. Blocking serotonin reuptake at the presynaptic neuron
C. Increasing dopamine release
D. Activating GABA receptors
Correct Answer: B
Rationale: SSRIs selectively inhibit the serotonin transporter (SERT) at the presynaptic neuron,
preventing serotonin reuptake and increasing serotonin availability in the synaptic cleft.
Question 5
A patient on an MAOI develops severe hypertension after eating aged cheese. This reaction is caused by:
A. Increased serotonin levels
B. Tyramine-induced norepinephrine release
C. Dopamine excess
D. Acetylcholine blockade
Correct Answer: B
Rationale: Aged cheese contains tyramine, which normally is broken down by MAO in the gut. MAOIs
block this breakdown, allowing tyramine to enter systemic circulation and trigger massive
norepinephrine release, causing hypertensive crisis.
Question 6
The therapeutic effect of lamotrigine (Lamictal) in bipolar maintenance is primarily due to:
A. Dopamine blockade
B. Glutamate inhibition via sodium channel blockade
C. GABA potentiation
D. Serotonin reuptake inhibition
Correct Answer: B
,Rationale: Lamotrigine inhibits voltage-gated sodium channels, reducing glutamate release. This
stabilizes neuronal membranes and is particularly effective for preventing depressive episodes in bipolar
disorder.
Question 7
Which brain structure is most implicated in the pathophysiology of Post-Traumatic Stress Disorder
(PTSD)?
A. Basal ganglia
B. Amygdala
C. Thalamus
D. Cerebellum
Correct Answer: B
Rationale: The amygdala plays a central role in fear conditioning and emotional memory. In PTSD, the
amygdala is hyperactive, leading to exaggerated fear responses, while the prefrontal cortex shows
reduced inhibitory control.
Question 8
Dopamine hyperactivity in the mesolimbic pathway is most associated with which symptom of
schizophrenia?
A. Anhedonia
B. Avolition
C. Hallucinations and delusions
D. Cognitive impairment
Correct Answer: C
Rationale: Mesolimbic dopamine hyperactivity is linked to positive symptoms of schizophrenia,
including hallucinations and delusions. This is why antipsychotics work by blocking D2 receptors in this
pathway.
Question 9
A patient on clozapine (Clozaril) requires regular monitoring of Absolute Neutrophil Count (ANC) due to
risk of:
A. Tardive dyskinesia
B. Agranulocytosis
C. Metabolic syndrome
D. Seizures
Correct Answer: B
, Rationale: Clozapine carries a black box warning for agranulocytosis (ANC <500/mm³), a potentially fatal
condition. The REMS program requires regular ANC monitoring: weekly for first 6 months, biweekly for
next 6 months, then monthly.
Question 10
The primary mechanism of benzodiazepines is:
A. Blocking dopamine D2 receptors
B. Enhancing GABA-A receptor chloride channel opening
C. Blocking serotonin reuptake
D. Antagonizing glutamate NMDA receptors
Correct Answer: B
Rationale: Benzodiazepines bind to GABA-A receptors, enhancing the affinity of GABA and increasing
chloride channel opening frequency. This hyperpolarizes neurons, producing anxiolytic, sedative, and
anticonvulsant effects.
Question 11
Which of the following is a negative symptom of schizophrenia?
A. Hallucinations
B. Delusions
C. Avolition
D. Agitation
Correct Answer: C
Rationale: Avolition (lack of motivation) is a negative symptom. Hallucinations, delusions, and agitation
are positive symptoms. Negative symptoms also include anhedonia, asociality, and blunted affect.
Question 12
A patient is started on lithium for bipolar disorder. Baseline laboratories should include:
A. CBC, CMP, and troponin
B. BUN, creatinine, TSH, and pregnancy test (if female)
C. LFTs, amylase, and lipase
D. ESR and CRP
Correct Answer: B
Rationale: Before starting lithium, obtain renal function (BUN, creatinine) to assess excretion
capacity, TSH (lithium causes hypothyroidism), and pregnancy test due to Ebstein's anomaly risk.
Organic and Physical Chemistry JUNE
2025 Mark Scheme
Question 1
Serotonin (5-HT) is primarily synthesized in which brain structure?
A. Locus coeruleus
B. Substantia nigra
C. Raphe nuclei
D. Nucleus accumbens
Correct Answer: C
Rationale: Serotonin is synthesized in the raphe nuclei of the brainstem. The locus coeruleus produces
norepinephrine, the substantia nigra produces dopamine, and the nucleus accumbens is part of the
reward pathway involved in dopamine transmission.
Question 2
Which neurotransmitter is primarily associated with the "fight or flight" response and is the target of
beta-blockers?
A. Acetylcholine
B. Dopamine
C. Norepinephrine
D. GABA
Correct Answer: C
Rationale: Norepinephrine mediates the sympathetic "fight or flight" response. Beta-blockers (e.g.,
propranolol) block norepinephrine receptors, reducing heart rate, blood pressure, and physical anxiety
symptoms.
Question 3
A patient experiencing EPS from antipsychotic medication is given benztropine (Cogentin). Which
neurotransmitter system is primarily affected by this treatment?
A. Serotonin
B. Dopamine
C. Acetylcholine
D. Glutamate
,Correct Answer: C
Rationale: Benztropine is an anticholinergic medication that blocks acetylcholine receptors. By reducing
acetylcholine activity, it helps restore the balance between dopamine and acetylcholine in the basal
ganglia, alleviating EPS symptoms.
Question 4
The mechanism of action of SSRIs involves:
A. Blocking norepinephrine reuptake only
B. Blocking serotonin reuptake at the presynaptic neuron
C. Increasing dopamine release
D. Activating GABA receptors
Correct Answer: B
Rationale: SSRIs selectively inhibit the serotonin transporter (SERT) at the presynaptic neuron,
preventing serotonin reuptake and increasing serotonin availability in the synaptic cleft.
Question 5
A patient on an MAOI develops severe hypertension after eating aged cheese. This reaction is caused by:
A. Increased serotonin levels
B. Tyramine-induced norepinephrine release
C. Dopamine excess
D. Acetylcholine blockade
Correct Answer: B
Rationale: Aged cheese contains tyramine, which normally is broken down by MAO in the gut. MAOIs
block this breakdown, allowing tyramine to enter systemic circulation and trigger massive
norepinephrine release, causing hypertensive crisis.
Question 6
The therapeutic effect of lamotrigine (Lamictal) in bipolar maintenance is primarily due to:
A. Dopamine blockade
B. Glutamate inhibition via sodium channel blockade
C. GABA potentiation
D. Serotonin reuptake inhibition
Correct Answer: B
,Rationale: Lamotrigine inhibits voltage-gated sodium channels, reducing glutamate release. This
stabilizes neuronal membranes and is particularly effective for preventing depressive episodes in bipolar
disorder.
Question 7
Which brain structure is most implicated in the pathophysiology of Post-Traumatic Stress Disorder
(PTSD)?
A. Basal ganglia
B. Amygdala
C. Thalamus
D. Cerebellum
Correct Answer: B
Rationale: The amygdala plays a central role in fear conditioning and emotional memory. In PTSD, the
amygdala is hyperactive, leading to exaggerated fear responses, while the prefrontal cortex shows
reduced inhibitory control.
Question 8
Dopamine hyperactivity in the mesolimbic pathway is most associated with which symptom of
schizophrenia?
A. Anhedonia
B. Avolition
C. Hallucinations and delusions
D. Cognitive impairment
Correct Answer: C
Rationale: Mesolimbic dopamine hyperactivity is linked to positive symptoms of schizophrenia,
including hallucinations and delusions. This is why antipsychotics work by blocking D2 receptors in this
pathway.
Question 9
A patient on clozapine (Clozaril) requires regular monitoring of Absolute Neutrophil Count (ANC) due to
risk of:
A. Tardive dyskinesia
B. Agranulocytosis
C. Metabolic syndrome
D. Seizures
Correct Answer: B
, Rationale: Clozapine carries a black box warning for agranulocytosis (ANC <500/mm³), a potentially fatal
condition. The REMS program requires regular ANC monitoring: weekly for first 6 months, biweekly for
next 6 months, then monthly.
Question 10
The primary mechanism of benzodiazepines is:
A. Blocking dopamine D2 receptors
B. Enhancing GABA-A receptor chloride channel opening
C. Blocking serotonin reuptake
D. Antagonizing glutamate NMDA receptors
Correct Answer: B
Rationale: Benzodiazepines bind to GABA-A receptors, enhancing the affinity of GABA and increasing
chloride channel opening frequency. This hyperpolarizes neurons, producing anxiolytic, sedative, and
anticonvulsant effects.
Question 11
Which of the following is a negative symptom of schizophrenia?
A. Hallucinations
B. Delusions
C. Avolition
D. Agitation
Correct Answer: C
Rationale: Avolition (lack of motivation) is a negative symptom. Hallucinations, delusions, and agitation
are positive symptoms. Negative symptoms also include anhedonia, asociality, and blunted affect.
Question 12
A patient is started on lithium for bipolar disorder. Baseline laboratories should include:
A. CBC, CMP, and troponin
B. BUN, creatinine, TSH, and pregnancy test (if female)
C. LFTs, amylase, and lipase
D. ESR and CRP
Correct Answer: B
Rationale: Before starting lithium, obtain renal function (BUN, creatinine) to assess excretion
capacity, TSH (lithium causes hypothyroidism), and pregnancy test due to Ebstein's anomaly risk.
