The Inquiry Cycle
How a scientific investigation works
Scientists do not just do random experiments. Every investigation follows a structured path so results can be trusted and repeated by others.
Observation / Question
→
Hypothesis
→
Method / Plan
→
Collect Data
→
Analyse
→
Conclude
What makes a good scientific question?
A good question is testable — it can be investigated by changing and measuring something. It names one thing that will be changed and what outcome you expect to measure.
✅ Good: "How does the temperature of water affect the time taken for sugar to dissolve?"
❌ Too vague: "How does temperature affect dissolving?" — dissolving what? measured how?
Hypothesis
A hypothesis is an educated prediction written as an "if … then …" statement that links your independent variable to your dependent variable.
Formula: "If [independent variable] increases / decreases, then [dependent variable] will increase / decrease because [brief reason from existing knowledge]."
Example: "If the temperature of the water increases, then the time taken for the sugar to dissolve will decrease because higher temperature gives particles more energy to move and collide."
Variables — the Core Concept
Three types of variable — know all three
| Variable | What it is | Example (sugar dissolving) |
|---|
| Independent (IV) | The one factor you deliberately change | Temperature of water (20°C, 40°C, 60°C, 80°C) |
| Dependent (DV) | What you measure or observe as a result | Time taken for all sugar to dissolve (seconds) |
| Controlled (CV) | Everything else you keep the same so they do not affect the result | Mass of sugar, volume of water, type of sugar, stirring rate, container size |
⚠ Common trap: Many students write "amount of water" as a controlled variable. In exam marking, this is too vague — write "volume of water (e.g. 100 cm³)" and include a specific value where possible.
How to identify variables in a question
Read the scenario. Ask yourself:
- What is being changed on purpose? → IV
- What is being measured to see if it changes? → DV
- What must stay the same for the test to be fair? → CV (list at least 2)
Designing a Fair Test
What makes a test "fair"?
A fair test changes only one variable at a time (the IV). All other variables that could affect the outcome (CVs) are kept constant. This means any change in the DV can only be caused by the IV.
If you change two things at once, you cannot tell which one caused the result. That is an unfair test and the data is unreliable.
Improving reliability
- Repeat readings — carry out the experiment at least 3 times for each value of the IV.
- Calculate the mean — average the repeated readings to reduce the effect of random error.
- Identify anomalies — an anomalous result is one that does not fit the pattern. Note it, check if an error occurred, and do not include it in the mean without reason.
- Use appropriate instruments — a measuring cylinder is more accurate than estimating; a stopwatch is more reliable than counting.
- Use a wider range of IV values — more data points give a clearer trend.
Improving accuracy
- Read measurements at eye level to avoid parallax error (especially with liquid meniscus in measuring cylinders).
- Use calibrated instruments and check the zero.
- Make sure instruments are appropriate — e.g. a 10 cm³ measuring cylinder is more accurate than a 100 cm³ one for small volumes.
Recording Data
Drawing a results table
Every results table needs:
- A heading row with the variable name and its unit in brackets, e.g. Temperature (°C)
- The IV in the first column, DV readings in subsequent columns
- Space for repeated readings and a mean column
Example table structure for the sugar experiment:
| Temperature of water (°C) | Time 1 (s) | Time 2 (s) | Time 3 (s) | Mean time (s) |
|---|
| 20 | | | | |
| 40 | | | | |
| 60 | | | | |
| 80 | | | | |
Graphs
- IV on the x-axis, DV on the y-axis — always.
- Label both axes with name and unit.
- Choose a scale that uses at least half the grid.
- Plot points with a small cross (×), not a dot.
- Draw a line of best fit (smooth curve or straight line) — do not join points dot-to-dot.
- Give the graph a title: "[DV] against [IV]"
Conclusions & Evaluation
Writing a conclusion
A strong conclusion does three things:
- States the trend — e.g. "As temperature increased, the time taken to dissolve decreased."
- Refers to data — e.g. "At 20°C it took 120 s but at 80°C it took only 18 s."
- States whether the hypothesis was supported — e.g. "This supports the hypothesis that higher temperatures increase dissolving rate."
Evaluating the investigation
After concluding, consider how the experiment could be improved:
- Reliability: "More repeats could be done and anomalous results removed from the mean."
- Accuracy: "A thermometer with smaller divisions could be used to measure temperature more precisely."
- Validity: "The experiment could be extended to test a wider range of temperatures."
Lab Safety
General rules
- Always wear safety goggles when heating liquids or using chemicals.
- Tie long hair back; do not wear loose clothing near flames.
- Never taste or smell chemicals directly — waft with your hand.
- Report spills and breakages to the teacher immediately.
- Know the location of the fire extinguisher, eye wash station and first aid kit.
Specific safety precautions (common exam answers)
| Situation | Safety precaution |
|---|
| Using a Bunsen burner / heating | Use a heat-proof mat; do not leave flame unattended; tie hair back |
| Using acids or alkalis | Wear goggles; wash hands after; avoid skin contact |
| Using sharp instruments (scalpel, scissors) | Cut away from the body; use a cutting board; handle with care |
| Using glassware | Check for cracks before use; handle carefully; do not heat cold glass directly |
| Electrical experiments | Check for frayed wires; switch off before changing connections; keep water away |
⚠ Exam tip: When asked for a safety precaution, be specific. "Be careful" scores zero marks. Name the hazard and the action: "Wear safety goggles to protect the eyes from acid splashes."
Practice Questions
Question 1 — Variable identification
A student investigates whether the height from which a ball is dropped affects the height of its bounce. She drops the ball from 20 cm, 40 cm, 60 cm and 80 cm and measures the bounce height each time. She repeats each drop three times.
- Identify the independent variable.
- Identify the dependent variable.
- State two controlled variables.
- Explain how the student improved the reliability of her results.
▶ Show Answer
- IV: Height from which the ball is dropped (cm)
- DV: Height of the ball's bounce (cm)
- CV (any two): Type of ball / mass of ball / type of surface / angle of drop / same person dropping
- She repeated each drop three times and could calculate a mean bounce height, reducing the effect of random error.
Question 2 — Fair test and safety
A student wants to test whether adding fertiliser affects how tall a bean plant grows. She plants 5 beans in identical pots. Three pots receive fertiliser, two pots receive only water.
- State one way this investigation is NOT a fair test.
- How should the student improve it?
- State one safety precaution when using fertiliser solution.
▶ Show Answer
- She has an unequal number of pots in each group (3 with fertiliser, 2 without), so results are harder to compare fairly.
- Use the same number of pots in each group (e.g. 3 pots with fertiliser and 3 pots with water only), and ensure all other conditions (soil type, pot size, watering volume, light, temperature) are identical.
- Avoid skin contact with fertiliser solution; wash hands after handling it / wear gloves.
Question 3 — Conclusion writing
A student measures the dissolving time of a sugar cube in water at different temperatures. Results: 20°C → 95 s, 40°C → 52 s, 60°C → 31 s, 80°C → 14 s. Write a conclusion for this experiment.
▶ Show Answer
As the temperature of the water increased from 20°C to 80°C, the time taken for the sugar to dissolve decreased from 95 s to 14 s. This shows that higher water temperature increases the rate of dissolving. The hypothesis is supported. This is because water molecules at higher temperatures have more energy and move faster, colliding with the sugar particles more frequently and breaking them apart more quickly.
Must-Know Checklist
Before the exam, make sure you can:
- Identify the independent, dependent and controlled variables in any scenario
- Explain what a fair test means and why it is necessary
- Describe how to improve reliability (repeats, mean, anomaly detection)
- Draw a correctly structured results table with headings and units
- Write a conclusion that includes trend, data reference and hypothesis judgement
- State a specific safety precaution linked to the hazard in the scenario
- Suggest a realistic improvement to any described investigation