Cambridge O Level Biology · Syllabus 5090 · Biological Molecules
Inference
What is Inference?
A conclusion drawn from an observation using scientific knowledge. In food testing, the observation is what was seen in the tube, such as a blue solution turning brick-red with a precipitate; the inference is what that shows, such as a reducing sugar being present at a detectable level. A positive result supports the presence of the substance tested for, while a negative result shows only that the substance was not detected under the conditions used.
This definition is part of the Biological Molecules chapter in Cambridge O Level Biology.
Common mistakes with Inference
- “Starch turned the iodine blue-black.” (Written in the observation column.) Repair Observation: “the orange-brown solution turned blue-black”. Inference: “starch is present”. You saw a colour, not a molecule. Where it costs Papers 3 and 4 award separate marks for the observation and the conclusion. Merging them can lose both.
Questions students ask about Inference
How do I write an observation and a conclusion so that both score?
Write what you saw, then what it means, as two separate statements. Observation: "the orange-brown iodine solution turned blue-black." Inference: "starch is present." Always give the starting colour as well as the final one. For a negative result write "not detected under these conditions", never "contains none", because a concentration below the detection limit looks exactly the same as none at all. Papers 3 and 4 award separate marks for the observation and for the conclusion.