HSC Investigating Science Practice Questions

Model answer.

Variables. The independent variable is the previous night's sleep (grouped as at least 8 hours, or less than 8 hours), measured with a wearable sleep tracker and checked against a sleep diary. The dependent variable is heart-rate recovery: the fall in heart rate (beats per minute) in the first 60 seconds after exercise stops. Controlled variables: the same step test for everyone (30 cm step, 3 minutes, in time with a metronome at 96 beats per minute), the same time of day (9 am), no caffeine or energy drinks for 12 hours beforehand, no vigorous exercise that morning, and the same heart-rate monitor.

Sample. Recruit at least 30 healthy Year 11 and 12 students with similar fitness (for example, all playing similar amounts of sport), excluding anyone with a heart or respiratory condition. Each student is tested on five different mornings so each person contributes results after both longer and shorter sleeps, which controls individual differences in fitness.

Procedure. 1. Obtain ethics approval from the school, informed written consent from participants and from parents of students under 18, and explain the right to withdraw. 2. Each morning record the sleep duration from the tracker. 3. The student sits for 5 minutes and resting heart rate is recorded. 4. The student completes the step test. 5. Heart rate is recorded immediately on stopping and again after 60 seconds of seated rest; recovery = peak rate minus rate at 60 seconds. 6. Repeat on five mornings over two weeks. 7. Calculate mean recovery after at least 8 hours of sleep and after less than 8 hours, for each student and for the whole group, and compare using a column graph.

Safety and ethics. Stop the test if a student feels dizzy or unwell; keep data confidential by using codes instead of names; sleep is not deliberately restricted, so no one is harmed.

Marking guidance (6 marks). Award marks for: identifying the independent and dependent variables and how each is measured; at least three relevant controlled variables; an appropriate sample size and selection; repetition to improve reliability; a clear, sequential procedure that someone else could follow; and an ethical or safety consideration. A list of steps with no controlled variables or measurement detail is limited to 2-3 marks.