Updated: 19 October 2026
Scientific answers should connect an observation to a reason. This original Grade 9 practice set focuses on interpreting evidence rather than memorising isolated definitions. The questions use supplied data and do not require learners to conduct unsupervised experiments.
On this page: original practice, explained answers and 20 short FAQs. Complete the tasks before reading the answers.
Read the information before naming a process
Underline the quantity measured, its unit and what was changed. Distinguish the measured result from your explanation. A table showing faster change is evidence; the reason for the change is an inference that must fit the science.
Work through a fair-test example
Two similar plants receive equal water and soil but different light conditions. A conclusion about light is more useful when other relevant conditions are controlled. One plant per treatment gives weak evidence, so repeated trials and several comparable plants improve confidence.
Record corrections as evidence statements
After marking, write one sentence beginning “The result shows…” and another beginning “This supports…”. This separates data from explanation and helps you avoid claiming more than an investigation establishes.
Practice questions and explained answers
1. A material has mass 120 g and volume 40 cm³. Calculate its density.
Show suggested answer
Density = mass/volume = 120/40 = 3 g/cm³.
2. In a plant-light investigation, name the changed variable and one control.
Show suggested answer
Changed variable: light condition. One suitable control: the amount of water supplied, using otherwise comparable plants.
3. Water readings are 20°C, 24°C and 28°C at equal time intervals. What pattern is shown?
Show suggested answer
The temperature rises by 4°C in each interval. The data alone do not identify the heat source.
4. A bulb goes out when one wire is disconnected from a simple series circuit. Explain.
Show suggested answer
The conducting path is broken, so current no longer flows through the bulb.
5. Why should a learner not smell an unknown chemical directly?
Show suggested answer
An unknown substance may release harmful vapour. Follow teacher-approved safety instructions and do not investigate unknown materials independently.
6. A microscope image is 30 mm long. The specimen is 0.3 mm long. Find magnification.
Show suggested answer
Magnification = image length/actual length = 30/0.3 = 100 times.
7. Three repeated lengths are 10.1, 10.2 and 10.3 cm. Find the mean.
Show suggested answer
Total = 30.6 cm; mean = 30.6/3 = 10.2 cm.
8. A food chain is grass → grasshopper → frog. What does the arrow show?
Show suggested answer
It shows the direction of energy transfer from the organism eaten to the consumer, not where the consumer moves.
9. Why is “the liquid turned blue” different from “copper ions are present”?
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The first is an observation. The second is an inference that requires an appropriate test and supporting evidence.
10. Can one unusual measurement prove a general rule?
Show suggested answer
No. Check the procedure, repeat measurements and consider whether the evidence is sufficient.
Frequently asked questions
What is a control variable?
A condition kept comparable so the effect of the changed variable can be interpreted.
What is the dependent variable?
The quantity measured or observed as the outcome.
Why repeat an investigation?
Repeats reveal variation and help identify unreliable results.
Should every graph pass through the origin?
No. Follow the data and scientific relationship.
What belongs on graph axes?
The quantity name and unit, with a suitable scale.
Is magnification measured in millimetres?
No. It is a ratio when lengths use the same units.
Why keep units in calculations?
They show what the number means and expose conversion errors.
Can safety rules be ignored in revision?
No. Practical preparation includes safe decisions.
How do I justify a conclusion?
Refer to a specific pattern or comparison in the evidence.
What should I do with an anomalous result?
Investigate and repeat where appropriate rather than deleting it without explanation.
What does density compare?
Mass with volume for the material being considered.
Can the heating pattern predict every later reading?
Only cautiously; a short pattern does not guarantee unchanged future conditions.
What is a complete circuit?
A continuous conducting path through the relevant components.
Why not identify a chemical from colour alone?
Several substances can share an appearance, so a suitable test is needed.
How do I convert millimetres for magnification?
Use the same unit for both image and actual length before dividing.
What is the role of the mean in repeats?
It summarises the repeated measurements but does not remove all experimental error.
Can energy return through a food chain arrow?
The arrow represents transfer in the direction shown, not a reversible movement of organisms.
Should an observation contain a guess?
Record what is detected; place the explanation in a separate inference.
How can I improve a graph description?
Name the variables, direction and a specific numerical comparison.
Where can I find broader subject practice?
Use the Integrated Science directory linked below the exercise.
Related revision resources
- Integrated Science KJSEA revision
- Junior School Practical Skills Revision Kit
- Grade 9 Topical Questions and Answers
- KJSEA English Composition Practice: Three Original Writing Tasks
- KJSEA Kiswahili Insha: Mazoezi Matatu na Mwongozo
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For official assessment notices and examination instructions, consult KNEC. These practice answers are not official scoring guides.
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