AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), 2020: Question 2

✅ Correct answer

A full-mark answer should say:

• The stimulus is detected by a receptor in the skin.
• An electrical impulse travels along a sensory neurone.
• The impulse passes through a relay neurone in the spinal cord and across synapses as a chemical.
• The impulse then travels along a motor neurone to the muscle, which contracts.

💡 Key knowledge

• A reflex action is rapid and automatic.
• The pathway is: receptor → sensory neurone → relay neurone → motor neurone → effector.
• At synapses, the signal crosses as a chemical neurotransmitter.
• The muscle is the effector because it carries out the response.

🧠 Exam technique

• Use the exact order of the reflex arc.
• Include both neurone types and the spinal cord.
• To get 4 marks, write a chain of events, not just a list of body parts.

❌ Common errors

• Saying the impulse goes straight from the skin to the muscle.
• Mixing up sensory and motor neurones.
• Forgetting the relay neurone or the synapse.
• Writing “signal travels as electricity all the way” — it changes to a chemical across synapses.

✅ Correct answer

A strong method would include:

• Test at least 3 people (more is better).
• Measure reaction time with the right hand at least 3 times for each person.
• Repeat the test with the left hand for the same people.
• Keep the test fair: same person dropping the ruler, same starting position, same distance, same instructions, same time of day, and same conditions.
• Calculate the mean reaction time for each hand and ignore anomalies if appropriate.

💡 Key knowledge

• The question is about whether hand used changes reaction time.
• A valid investigation must compare right hand vs left hand on the same people.
• Using a reaction ruler is a common GCSE method.
• Reliable results come from repeats and a mean.

🧠 Exam technique

• Write the method in a clear sequence: select people → test right hand → test left hand → repeat → calculate mean.
• Say how the result will be measured: for example, distance the ruler falls before being caught or convert to reaction time if needed.
• Include control variables to show the test is fair.

❌ Common errors

• Testing only one hand or only one person.
• Not repeating the test.
• Giving vague advice like “do a test” without saying how.
• Forgetting to compare the two hands of each person.

📐 Calculation

1. Add the six times: 0.2 + 0.4 + 0.3 + 0.4 + 0.2 + 0.3 = 1.8
2. Divide by the number of values: 1.8 ÷ 6 = 0.3
3. So, X = 0.3 seconds

🧠 Exam technique

• Mean = sum of values ÷ number of values.
• Show working to get method marks.
• Keep the answer to a sensible number of decimal places, matching the table.

❌ Common errors

• Adding incorrectly.
• Dividing by the wrong number.
• Forgetting the unit.
• Writing 0.03 instead of 0.3 because of decimal place mistakes.

✅ Correct answer

Reaction time (or time).

💡 Key knowledge

• The dependent variable is what the student measures.
• Here, the measured outcome is the reaction time in seconds.

❌ Common errors

• Giving the independent variable instead, such as hand used.
• Writing “tennis” — that is the group being compared, not the measurement.

✅ Correct answer

The people who play tennis had a shorter mean reaction time than the people who do not play tennis.

💡 Key knowledge

• The conclusion is: “Playing tennis improves reaction time.”
• To support it, choose data showing the tennis group is faster on average.

🧠 Exam technique

• Use comparative language: shorter, faster, lower mean.
• If possible, mention the mean values: the tennis group’s mean is 0.3 s and the non-tennis group’s mean is 0.4 s.

✅ Correct answer

Any one of these would score the mark:

• There is an overlap in times between the two groups.
• There is only a small difference in the mean times.
• The sample is small.

A clear example from the table: some people who do not play tennis had times as low as 0.2 s, which is the same as the tennis group.

💡 Key knowledge

• Evidence that weakens the conclusion shows the result is not clear-cut.
• Looking at individual values can reveal overlap.
• A small group of six people in each set means the sample is limited.

❌ Common errors

• Repeating the supporting evidence instead of challenging it.
• Saying “the conclusion is wrong” without using data.
• Forgetting that one low score in the non-tennis group weakens the conclusion.

💡 Top-scoring reflex answer

A receptor detects the stimulus, an electrical impulse travels along sensory neurone → relay neurone → motor neurone, crossing synapses as a chemical, and the muscle contracts.

💡 Top-scoring method answer

Compare the same people’s right and left hands, repeat each test, keep conditions the same, and calculate a mean.

💡 Top-scoring data answer

Use the numbers in the table: tennis players have a shorter mean reaction time, but the data overlap so the conclusion is not fully secure.