An observation says what you saw. An inference says why it happened. A conclusion says whether the hypothesis holds.
This lesson is part of biological investigation in the SPM Biology subject guide. You should have a clear hypothesis first, as in writing a testable hypothesis.
How do the three differ?
| Type | Answers | Starter | Contains |
|---|---|---|---|
| Observation | What did I see or measure? | “The number of bubbles was…” | Measured facts, units |
| Inference | Why did it happen? | “This is because…” | A biological reason |
| Conclusion | Is the hypothesis supported? | “The hypothesis is accepted because…” | Verdict plus evidence |
Worked example: yeast and temperature
Original results. Yeast in sugar solution, bubbles of gas counted in two minutes.
| Temperature (°C) | Bubbles |
|---|---|
| 5 | 3 |
| 25 | 26 |
| 35 | 42 |
| 55 | 6 |
Hypothesis: the higher the temperature up to 35 °C, the more carbon dioxide yeast produces.
Observation. The number of bubbles rose from 3 at 5 °C to 42 at 35 °C, then fell to 6 at 55 °C.
Inference. Yeast respired faster at 35 °C, producing more carbon dioxide, because the enzymes worked fastest near that temperature. At 55 °C the enzymes were probably denatured, so the bubbles dropped.
Conclusion. The hypothesis is accepted for temperatures from 5 °C to 35 °C, because the bubbles increased from 3 to 42. Above 35 °C the rate fell, so the trend does not continue.
A common mistake: an inference written as an observation
| Sentence | Type |
|---|---|
| Yeast respired faster at 35 °C. | Inference: respiration is not seen directly |
| 42 bubbles formed at 35 °C. | Observation: counted and measured |
You cannot see respiration rate directly. You see the bubbles. A results section should state only what was measured, so keep explanations for the inference step.
Checking your own sentences
Read each sentence and ask: could I photograph this or count it? If yes, it is an observation. If it needs a biological reason, it is an inference. If it says “accepted” or “rejected”, it is a conclusion.
Check yourself
A seedling in a dark box grows 12 cm in a week and looks pale yellow. Another in light grows 6 cm and stays green. Write one observation, one inference and a conclusion for the hypothesis: “A seedling grows taller in the dark”.
Answer
Observation: the seedling in the dark grew 12 cm and was pale yellow, but the seedling in light grew 6 cm and was green.
Inference: the seedling in the dark grew tall to reach light, and it was yellow because chlorophyll forms only in light.
Conclusion: the hypothesis is accepted, because the seedling in the dark grew 12 cm, taller than the 6 cm in the light.
What to study next
Try the biological investigation practice set, and use the biological data interpretation trainer for more data.
If you want a teacher to sort your results sentences with you, see online one-to-one Biology tuition.