Introduction
This PSLE Science question tests students’ understanding of experimental setup, controlled variables, and fair tests.
The teacher carefully analyses each diagram to ensure that only one variable changes while all other conditions remain the same.
The goal: identify the correct experimental setup that creates a fair comparison.
The Question
The exam shows four different experimental setups, each trying to test a condition about plant growth.
Students must identify which setup is a proper experiment with:
- One changed variable (the independent variable)
- All other conditions kept constant (controlled variables)
- A measurable outcome (dependent variable)
The teacher concludes that the correct answer is Option (2).
Step-by-Step Explanation (Following Teacher’s Working)
Step 1 — Identify the purpose of the experiment
The question requires comparing plant growth under different conditions.
Thus, one factor must change — but everything else must remain identical.
Step 2 — Check each setup for fairness
The teacher’s notes show:
- Some setups changed too many variables
- Some setups did not include a proper control
- Some setups were comparing different conditions incorrectly
For example:
❌ Some had different amounts of soil
❌ Some used different types of plants
❌ Some changed more than one factor at the same time
❌ Some lacked a control setup
All these make the experiment invalid.
Step 3 — Why Option (2) is correct
✔ Both setups have:
- Same plant type
- Same number of seeds
- Same container size
- Same soil
- Same amount of water
- Same environmental conditions
✔ Only ONE variable is changed, making it a fair test.
✔ The comparison directly answers the scientific aim.
Therefore, the only correct experimental setup is Option (2).
Key Concepts
| Concept | Explanation |
| Independent Variable | The factor you change |
| Dependent Variable | What you measure |
| Controlled Variables | Everything you keep the same |
| Fair Test | Exactly one variable is changed |
Tips for Students
✔ Always check whether only one variable is changed.
✔ Look for changes in soil, water, seed type, container size, or light — these are common traps.
✔ A good experiment always includes a control setup.
✔ If more than one thing changes, the experiment is invalid.
For Parents
Students often struggle not with knowledge but with identifying experimental fairness.
This topic frequently appears in PSLE Science, and understanding it makes 4–6 MCQs much easier.
Practising with real exam diagrams improves accuracy significantly.