This page explains 14 terms that students commonly swap or blur in Combined Science. Each entry gives a plain meaning, a short example, the term it is most often confused with, and the lesson that teaches it in context.
Your syllabus decides which terms you must know and how deeply. Check it on the Cambridge page before treating any entry as a requirement. The English, BM and Chinese concept bridge shows the same concepts in three languages.
Reasoning and evidence terms
Observation. What you see, measure or record, with no explanation added. Example: the solution turned from red to blue. Confused with inference, which is the conclusion you draw from an observation. Practise in observation versus inference across two chemical tests.
Independent, dependent and control variables. The independent variable is the one you change, the dependent variable is the one you measure, and control variables are kept the same. Example: changing light intensity, measuring bubbles per minute, keeping temperature constant. Students often confuse dependent and control. See identifying a controlled condition.
Accuracy and precision. Accuracy is how close a reading is to the true value, while precision is how close repeated readings are to each other. Example: a balance that reads 0.3 g too high gives precise but inaccurate results. See why repeated readings do not fix a biased method.
Anomaly. A result that does not fit the pattern of the others. Example: four plants measure about 12 cm and one measures 25 cm. It is not automatically an error, so investigate before removing it. See explaining an anomaly.
Conclusion and claim. A conclusion is what the evidence supports, and a claim can go further than the evidence. Example: “temperature affects rate” may be supported, “temperature always doubles rate” is not. See comparing a conclusion with an alternative.
Proportional and trend. Two quantities are proportional if doubling one doubles the other and the graph is a straight line through the origin. A trend only says they rise or fall together. See proportionality versus a general trend.
Biology terms
Respiration and breathing. Respiration is the chemical process in cells that releases energy from food. Breathing is moving air in and out of the lungs. They are often confused because both involve oxygen. See tracing energy between a biological process and a measurement.
Partially permeable membrane. A membrane that lets some substances through and blocks others. Example: water passes across a cell membrane, while large molecules stay inside. Confused with “a membrane with holes that everything passes through”. See connecting a cell observation with a membrane explanation.
Food chain and food web. A chain shows one feeding path, and a web shows the linked paths in a community. Example: if rabbits decline, a fox that also eats birds may survive. See using a food-web change to test a conclusion.
Chemistry terms
Particle. A general word for the tiny pieces matter is made of, which can be atoms, molecules or ions depending on the substance. Students sometimes use “atom” for everything. See using a particle model to explain a state observation.
Mixture and compound. A mixture is substances mixed without chemical bonding and can be separated by physical methods. A compound is chemically bonded and needs a chemical change to split. Example: sand in salt water is a mixture. See interpreting a separation sequence.
Mass change and conservation. Mass is conserved in a closed system. If a burned metal gains mass, the extra comes from oxygen in the air. See connecting an equation with a supplied mass change.
Physics terms
Mass and weight. Mass is the amount of matter and is measured in kilograms. Weight is a force caused by gravity and is measured in newtons. Example: your mass is the same on the Moon, but your weight is not. See applying a force relationship to a biological measurement.
Rate and amount. An amount is how much, while a rate is how much per unit of time. Example: 36 cm³ of gas is an amount, and 9 cm³ per minute is a rate. See moving from a graph to a rate calculation.
How do I use this list?
Pick the five terms you most often mix up. For each, write one sentence of your own that could not be true if you used the other term. Then test yourself with a fresh question from the original practice section.
Back to the learning guide. If you can recite definitions but still choose the wrong word in an answer, the Combined Science tuition page explains how one-to-one sessions can work on this.