AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), November 2021: Question 5

12 marks · Standard Demand difficulty · Short Answer

Investigate reaction time using stopwatches and analyze the neurological and hormonal effects of caffeine and adrenaline on the nervous system.

Practise this question

Question

The question presents an investigation on how caffeine affects reaction time involving eight pairs of female students using stopwatches. Sub-questions 05.1 and 05.2 ask for a control variable and two sources of random error. Table 1 lists decrease in reaction time for 8 pairs: pair 1 is 0.039 s, pair 2 is 0.021 s, pair 3 is 0.027 s, pair 4 is 0.041 s, pair 5 is 0.022 s, pair 6 is 0.036 s, pair 7 is 0.024 s, and pair 8 is 0.097 s. Sub-questions 05.3 and 05.4 ask why a mode cannot be determined and how the mean was calculated excluding the anomaly. Sub-question 05.5 asks how adrenaline's effect on heart rate decreases reaction time. Figure 5 depicts a synapse between a sensory neurone and a relay neurone showing caffeine and adenosine molecules interacting with adenosine receptors, followed by sub-questions 05.6 to identify gap X and 05.7 to explain why reaction time decreases when caffeine binds to these receptors.
Question text

05 Caffeine is a drug that decreases reaction time.

A group of sixteen students investigated the effect of caffeine on reaction time.

The students were all 15-year-old girls.

The group was divided into 8 pairs of students.

This is the method used.

1. Student A starts two stopwatches at the same time.

2. Student A then gives one of the stopwatches to Student B.

3. Student A says “stop” at the same time as stopping her stopwatch. Student B

stops her stopwatch as quickly as possible after Student A says “stop”.

4. The difference in time shown on the two stopwatches is recorded. This is the

reaction time of Student B.

5. Student B drinks a caffeinated drink.

6.The students wait 15 minutes and then repeat steps 1 to 4.

05.1 Suggest one control variable the students should have used in the investigation.

Do not refer to age or sex in your answer.

[1 mark]

05.2 Suggest two sources of random error when using this method to measure a person’s

reaction time.

[2 marks]

Table 1 shows the results.

Table 1

Student Decrease in reaction time after

pair drinking the caffeinated drink

in seconds

1 0.039

2 0.021

3 0.027

4 0.041

5 0.022

6 0.036

7 0.024

8 0.097

05.3 Why can a mode not be determined for the data in Table 1?

[1 mark]

05.4 The students decided the result from pair 8 was anomalous.

The students calculated that the mean decrease in reaction time was 0.030 seconds.

Describe how the students calculated the mean decrease in reaction time.

[1 mark]

05.5 Caffeine causes the release of adrenaline.

Adrenaline affects heart rate.

*18* Explain how the effect of adrenaline on heart rate might cause reaction time

to decrease.

[4 marks]

Adenosine is a different chemical made by the body.

Adenosine binds to receptors on relay neurones.

Adenosine decreases the number of impulses in relay neurones.

Figure 5 shows how caffeine binds to adenosine receptors on a relay neurone.

When caffeine binds to adenosine receptors it blocks the receptor so adenosine

cannot bind.

Figure 5

05.6 Label X shows the gap between the sensory neurone and the relay neurone.

What is the name of the gap labelled X?

[1 mark]

05.7 Suggest why reaction time decreases when caffeine binds to adenosine receptors.

[2 marks]

Mark scheme

Show the mark scheme The mark scheme outlines answers for parts 05.1 to 05.7: 05.1 accepts volume/intake of caffeine, sleep, or mass (1 mark); 05.2 accepts errors in pressing stopwatches simultaneously or anticipation/distraction (2 marks); 05.3 notes all values are different / no value occurs more than once (1 mark); 05.4 specifies adding the other 7 results and dividing by 7 (1 mark); 05.5 requires increasing heart rate, higher oxygen/glucose delivery, increased respiration rate, and more energy for muscle contraction (4 marks); 05.6 identifies gap X as a synapse (1 mark); 05.7 states fewer adenosine molecules can bind, leading to more frequent impulses in the relay neurone (2 marks). Total 12 marks.

AO /

Question Answers Extra information Mark

Spec. Ref.

allow named caffeinated drink

05.1 for caffeine AO1

any one from: 1 4.5.2

• previous intake of caffeine RPA6

that day

• usual intake of caffeine

(on previous days)

• concentration of caffeine allow amount / mass / type of

• volume of caffeine caffeine for 1 mark

• time of day

• amount of sleep allow fatigue

• body mass allow (body) weight / BMI

• previous experience of the

test

• which hand (of student B)

holds the stopwatch

05.2 any two from: 2 AO3

• (student A) does not press 4.5.2

both start buttons RPA6

simultaneously

• (student A) may not say stop

and press button

simultaneously

• student B could be distracted

• idea that student B

anticipated student A

stopping the stopwatch

• stopwatch malfunction

allow (stop)watches may not be

accurate

05.3 no value / result / number 1 AO2

occurs more than once 4.5.2

or RPA6

all the values / results / numbers

are different

05.4 add(ed) the other (7) results and allow correctly shown 1 AO2

16 divide(d) by 7 calculation 4.5.2

RPA6

ignore leave out the result for

pair 8

05.5 (adrenaline) increases heart rate allow increases blood flow 1 AO1

(which) increases oxygen / 1 AO1

glucose to brain / muscle (cells)

(which) increases rate of 1 AO2

respiration

(so) releasing more energy for allow (so) releasing more ATP 1 AO2

(faster / more) muscle for (faster / more) muscle

contraction contraction 4.5.3.6

do not accept energy produced 4.5.2

/ made / created

05.6 synapse allow synaptic cleft 1 AO1

4.5.2

05.7 fewer adenosine (molecules) 1 AO2

can bind to the receptors

or

adenosine has no / less effect

on the (relay) neurone

therefore impulses in relay allow impulses in relay neurone 1 AO3

neurone are more frequent are faster

allow there are more impulses in 4.5.2

relay neurone

allow impulses in relay neurone

not delayed / reduced (in

number)

ignore caffeine binds to

adenosine receptors

Total 12

How to answer it

Caffeine, Reaction Time & Synaptic Transmission

📋 What This Question Tests

This 12-mark question assesses Required Practical 6 (human reaction time), experimental design (variables, random errors, and data handling such as mode and calculating a mean while omitting anomalies), hormone action (adrenaline on heart rate and cellular respiration), and neurobiology (identifying a synapse and evaluating novel information on receptor competition).

Question 05.1 [1 Mark]

Control Variables in the Investigation

Suggest one control variable the students should have used. Do not refer to age or sex.

✅ Any One Acceptable Answer

  • Volume / mass / concentration of caffeinated drink
  • Previous caffeine intake that day (or usual daily intake)
  • Amount of sleep / fatigue
  • Body mass / weight / BMI
  • Time of day the test is carried out
  • Which hand student B uses to hold the stopwatch
  • Previous practice / experience with the stopwatch test

❌ Common Errors

  • Repeating age or gender/sex (expressly forbidden in the question stem).
  • Vague statements like "the drink" (must specify volume, brand, or concentration).
  • Confusing a control variable with the independent variable (caffeine intake).
Mark Scheme Note: 1 mark for any valid biological or procedural factor kept constant across pairs.
Question 05.2 [2 Marks]

Sources of Random Error in the Stopwatch Method

Suggest two sources of random error when using this method.

✅ Any Two Acceptable Answers

  • Student A does not press both start buttons simultaneously.
  • Student A does not say "stop" at the exact same instant as pressing their stop button.
  • Student B is distracted / loses concentration.
  • Student B anticipates Student A saying "stop" and presses early.
  • Stopwatch malfunction or lag in button mechanism.

🧠 Exam Technique

A random error causes measurements to be unpredictably higher or lower. Focus directly on human reaction variations between Student A and Student B, or button-press timing discrepancies.

Mark Scheme Note: [2 marks] 1 mark for each distinct, plausible reason why stopwatch timing might vary randomly between trials.
Questions 05.3 & 05.4 [2 Marks]

Data Handling: Mode and Calculating the Mean

05.3: Why can a mode NOT be determined? [1 mark]

✅ All values are different (no number occurs more than once in Table 1).

💡 Definition: The mode is the most frequently occurring value. Every pair has a unique time decrease.

05.4: Describe how the mean was calculated [1 mark]

Step-by-step description:

  1. Exclude the anomalous result (pair 8 = 0.097 s).
  2. Add together the remaining 7 values:
    0.039 + 0.021 + 0.027 + 0.041 + 0.022 + 0.036 + 0.024 = 0.210 s
  3. Divide the total by 7:
    0.210 ÷ 7 = 0.030 s

✅ Acceptable answer: "Add the other 7 results together and divide by 7."

❌ Trap to Avoid in 05.4

Simply writing "ignore pair 8" is insufficient! The question asks how the mean was calculated, so you must explicitly state adding the remaining 7 numbers and dividing by 7.

Question 05.5 [4 Marks]

Adrenaline and Reaction Time

Explain how the effect of adrenaline on heart rate might cause reaction time to decrease.

💡 The 4-Step Physiological Pathway

Link heart rate to cellular respiration and muscle action in a clear cause-and-effect sequence:

✅ 4-Mark Marking Points

  1. Point 1: Adrenaline increases heart rate (or increases blood flow).
  2. Point 2: Delivers more oxygen and glucose to brain / muscle cells.
  3. Point 3: Increases the rate of (aerobic) respiration.
  4. Point 4: Releases more energy / ATP for faster muscle contraction.

❌ Severe Examiner Trap

NEVER say "produces energy" or "creates energy"! Energy cannot be created. You will lose Point 4 if you say energy is made or produced. Always use the phrase: "releases energy" or "releases ATP".

Mark Breakdown: 1 mark per bullet point. High-scoring responses link oxygen/glucose delivery directly to cellular respiration and faster muscular response.
Questions 05.6 & 05.7 [3 Marks]

Synapses & Competitive Binding

05.6: Label X [1 mark]

✅ Synapse (also accept synaptic cleft or synaptic gap).

💡 Given Information Breakdown for 05.7

  • Adenosine decreases impulses in relay neurones.
  • Caffeine blocks adenosine from binding to its receptors.

05.7: Why reaction time decreases when caffeine binds [2 marks]

  1. Mark 1 (Receptor blocking): Fewer adenosine molecules can bind to the receptors (or adenosine has less / no effect on the relay neurone).
  2. Mark 2 (Impulse transmission): Therefore, electrical impulses in the relay neurone are more frequent (or faster / not reduced).

🧠 How to Tackle Novel Contexts (AO3)

The prompt says: "When caffeine binds... it blocks the receptor so adenosine cannot bind" and "Adenosine decreases impulses". Putting these two facts together: if the inhibitor (adenosine) is blocked, the neurone is not inhibited, meaning more impulses pass along the relay neurone, making reaction times faster (smaller).

Mark Scheme Note for 05.7: Ignore simply repeating that "caffeine binds to receptors" (that was given in the question stem). You must state the biological consequence on adenosine and nerve impulse frequency.

Topics

Biology · B5: Homeostasis and Response

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 2 (Higher), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.