PSLE Science Open-Ended Answers: Top 200 Words

PSLE Science open-ended questions reward correct scientific reasoning, not the longest possible answer. Pupils must read the instruction, interpret the diagram or graph, identify what the evidence shows and connect a valid scientific concept to the result. This Primary 6 guide explains 200 useful words and phrases for those tasks, including observation, inference, variables, graphs, fair tests and cause-and-effect language.

Consider a question showing that a plant becomes taller during a month. It would be correct to describe the increase shown by the graph, but not necessarily correct to claim sunlight caused it when the question gives no sunlight comparison. Likewise, a diagram of an open circuit tells you that a conducting pathway is interrupted, but a pupil must still explain that relationship when the question asks ‘why’. Small distinctions like these are often more useful than copying large answer templates.

Quick information:

For: Primary 6 Standard Science and PSLE-related scientific inquiry practice in Singapore.
Main searches addressed: PSLE Science open-ended questions, graph reading, experiment variables, fair tests, how to explain answers and scientific vocabulary.
Includes: exactly 200 numbered terms, ten clear sections, original worked examples, a four-week plan and parent FAQs.
Foundation Science note: some curriculum topics and examination requirements differ. Check the appropriate syllabus rather than assuming every term here is examinable.
Editorial scope: an independent eduKate glossary of reasoning language, not an official MOE or SEAB 200-word list.

Why scientific reasoning matters in PSLE Science

The MOE Primary Science Teaching and Learning Syllabus joins scientific knowledge with practices such as questioning, investigating, interpreting data, evaluating evidence and communicating explanations. These skills are not a separate vocabulary chapter that disappears after a test. They are used inside questions on living things, plants, human systems, energy, electricity, forces and interactions in the environment.

The Singapore Examinations and Assessment Board has illustrated that an open-ended Science investigation may allow more than one scientifically sound method. This is important for parents who worry that a pupil must reproduce one exact model sentence. The real goal is a clear and scientifically valid explanation of the relevant mechanism or procedure, supported by the conditions in the question. We do not reproduce any copyrighted examination question here; all worked examples are original.

There is also a difference between reading a word and using it correctly. ‘Predict’ asks what might happen under stated conditions. ‘Infer’ asks what can reasonably be interpreted from data. ‘Describe’ reports features or changes. ‘Explain’ supplies an appropriate cause or mechanism. A pupil who supplies a prediction when asked for an observation is answering the wrong question, even if the subject knowledge is sound.

Top 200 Primary 6 Science reasoning words and meanings

Each of the ten sections contains twenty terms and a practical reading exercise. Some measurement and statistical language is wider-reading preparation, not an assertion that every term is a required PSLE examination keyword. Read the short meanings, then practise them in one real Science diagram or data set.

1. Read the instruction before writing the answer

A pupil may know photosynthesis but lose clarity because the question asks for a reason and the child gives only a description. The command word sets the task.

Avoid this mistake: ‘Describe’ and ‘explain’ are not interchangeable. Description names features or events; explanation connects them to a mechanism.

Practice: Take one original Science question. Underline the command verb and write what kind of response it demands before answering.

state — Give the requested fact directly without unnecessary elaboration.
name — Provide the correct term or identity for something.
identify — Recognise the relevant object, variable, structure or process.
describe — Report pertinent features, observations or steps.
explain — Give a scientific reason connecting a condition to a result.
compare — Examine similarities and differences between two cases.
contrast — Focus on differences between situations or objects.
predict — Give a likely outcome before seeing the final result.
infer — Make a reasoned interpretation from observations or data.
suggest — Propose a plausible answer or possible method.
justify — Provide scientifically sound evidence or reasons for a choice.
evaluate — Judge the strength, usefulness or limitations of an approach.
interpret — Explain what data, a diagram or a statement means.
calculate — Work out a quantity using mathematical operations.
estimate — Give a sensible approximate value supported by information.
deduce — Reason from known facts to a more specific conclusion.
outline — Give the key steps or main points without full detail.
sequence — Arrange stages or events into the correct order.
label — Add names to the appropriate parts of a diagram.
annotate — Add explanatory notes to a drawing or figure.

2. Separate observation, inference and explanation

The water level fell in a dish. That is observable. ‘It evaporated’ is one possible explanation, but water could also have spilled or leaked.

Avoid this mistake: An inference is not a direct observation, and a scientific claim can be reasonable without being proven by one result.

Practice: Use a photo of a plant. Write one observation, one inference and one question that could test the inference.

observation — A detail or measurement recorded directly.
inference — An interpretation drawn from a set of observations.
hypothesis — An explanation proposed in a way that can be tested.
claim — A statement that may be evaluated against evidence.
reason — A justification connecting facts to an answer.
evidence — Relevant observations or measurements supporting a statement.
mechanism — The process through which a cause produces an effect.
cause — A factor contributing to an event or change.
effect — An outcome associated with an influencing condition.
conclusion — A statement of what the observations or test results support.
alternative explanation — Another cause that could account for the same observation.
assumption — A condition treated as true without being established in the question.
uncertainty — A limit to how confidently a result can be interpreted.
plausible — Reasonable given the scientific facts and evidence.
supported — Consistent with the available evidence and scientific concepts.
unsupported — Not established by the data or reasoning provided.
overgeneralisation — Extending a limited finding to more cases than evidence justifies.
contradiction — An inconsistency between statements or between a claim and data.
correction — A change that fixes an inaccurate claim or step.
scientific explanation — A reasoned connection between a result and an accepted concept.

3. Read diagrams as information, not decoration

A diagram of a plant or electric circuit provides clues about structure and connections. A child who overlooks one arrow or disconnected wire can reverse the answer.

Avoid this mistake: Do not infer a functioning path just because wires appear close. Check the actual connections and labels.

Practice: Choose a circuit or water-cycle diagram and say what each labelled arrow means in words.

diagram — A simplified drawing used to communicate selected facts or relationships.
schematic — A diagram showing connections or structure rather than realistic appearance.
symbol — An agreed mark representing a component or idea.
legend — A key explaining the meaning of graphical marks or colours.
arrow — A mark commonly indicating direction or connection.
direction — The way a quantity, movement or process acts.
pathway — The route followed by a substance, energy transfer or process.
connection — A link joining two components or parts.
junction — A point where connected routes meet or divide.
boundary — The limit separating one region or structure from another.
cross-section — A drawing of an object’s interior as if cut through.
magnification — Making a representation appear larger than its real size.
scale drawing — A representation in which sizes follow a stated proportion.
not to scale — A reminder that apparent proportions may not match reality.
caption — Short text explaining the purpose or content of an illustration.
key — An explanation of symbols used in a diagram.
apparatus diagram — A drawing showing equipment used in an investigation.
process diagram — A picture depicting steps or relationships in a process.
cycle diagram — A display with connected stages forming a repeated process.
food-web arrow — A mark pointing from food to the organism that consumes it.

4. Plan fair tests with a clear question

Two seedlings may differ in height, but if their pots, water, soil and light all differ, the cause of the result remains unclear.

Avoid this mistake: Only one relevant factor should be deliberately changed when testing its effect, while other major influences are kept comparable.

Practice: Design a safe investigation on how light exposure affects an observable plant response. Name the factor changed and the outcome recorded.

investigation — A planned attempt to answer a scientific question using evidence.
research question — A clear query that an investigation aims to resolve.
fair test — A comparison designed to control unrelated influences.
independent variable — The factor deliberately altered in an experiment.
dependent variable — The outcome measured or observed in response.
controlled variable — A relevant condition maintained as similar as practicable.
constant — A quantity or condition deliberately kept unchanged.
condition — An aspect of the setup that can influence the result.
factor — Something that may affect an experimental outcome.
treatment — A chosen condition or action applied to a tested sample.
control group — A comparison group not receiving the tested treatment; extension term.
test group — Samples exposed to the chosen condition or intervention.
baseline — A starting point used for later comparison.
procedure — The ordered steps used to run an investigation.
trial — One run of a planned method.
repeated trial — Another run performed under comparable conditions.
replication — Repeating an investigation to check whether findings are dependable.
sample — A selected item or set of cases used for investigation.
sample size — The number of items or observations included.
control of variables — Keeping relevant factors comparable so a cause can be examined.

5. Measure correctly and give units

A student may record a length but forget its unit, or confuse mass with weight. Those errors can make an otherwise correct comparison ambiguous.

Avoid this mistake: A number without units may not describe a physical quantity adequately. Do not use gram for time or millilitre for length.

Practice: Invent a table recording length, volume, mass and time. Give the appropriate equipment, unit and plausible measured values.

measurement — Finding a quantity with an agreed tool and reference.
unit — A standard used to communicate measured quantities.
centimetre — A length unit equal to 0.01 metre.
millimetre — A length unit equal to 0.001 metre.
metre — A standard SI unit of length.
gram — A unit of mass used for small everyday samples.
kilogram — A unit of mass equal to one thousand grams.
millilitre — A unit of volume equal to one-thousandth of a litre.
litre — A volume unit equal to one thousand millilitres.
second — A standard unit of time.
minute — A time interval equal to sixty seconds.
degree Celsius — A temperature unit used in everyday measurements.
newton — A unit of force, commonly used beyond basic primary measurement tasks.
ruler — A marked tool for measuring length.
balance — An instrument used for measuring mass.
thermometer — A device for measuring temperature.
measuring cylinder — A graduated vessel for measuring liquid volume.
stopwatch — A tool used to measure elapsed time.
accuracy — Closeness of a result to the correct or accepted value.
precision — How finely and consistently measurements are expressed or repeated.

6. Turn tables and graphs into statements

A chart may show that a plant grew taller each week, but it does not automatically show which environmental factor caused the growth.

Avoid this mistake: The direction of a graph does not by itself reveal cause. Check what the axes measure and which conditions were changed.

Practice: Make a simple graph of four original measurements and write one supported trend and one claim the graph cannot establish.

data — Recorded observations or measurements available for analysis.
data table — Information arranged in rows and columns for reading.
row — A horizontal series of entries in a table.
column — A vertical series of entries in a table.
heading — A label describing what a table section or column contains.
bar graph — A chart using bars to compare counts or amounts across categories.
line graph — A chart connecting numerical points to show variation.
horizontal axis — The reference line commonly running left to right.
vertical axis — The reference line commonly running bottom to top.
axis label — Text describing what a chart axis represents.
scale — The numerical spacing used for measurement or graphical display.
interval — The difference between neighbouring marked quantities.
data point — A single recorded value displayed in a graph.
plot — To place measured values at suitable positions on a chart.
trend — An overall direction or pattern across observations.
increase — A rise in the value of a measured quantity.
decrease — A fall in the value of a measured quantity.
fluctuation — A series of rises and falls in recorded values.
outlier — A point noticeably different from the general data pattern.
graph interpretation — Explaining what a chart shows without inventing extra evidence.

7. Understand relationships without claiming too much

A graph may show more rain during one month, but that does not prove rainfall is the only factor affecting plant growth or water use.

Avoid this mistake: Correlation is not always causation. A pattern may have multiple possible explanations.

Practice: Compare two observations that changed together. Write why one might influence the other and what further evidence would help.

relationship — A link between quantities, events or conditions.
association — Two conditions varying together without proof of a direct cause.
correlation — A tendency for quantities to change together; extension term.
causation — A relationship in which one factor contributes to an outcome.
dependency — A situation in which a result relies on another condition.
direct relationship — A pattern where two quantities rise or fall together.
inverse relationship — A pattern where one quantity falls as another rises.
proportion — A mathematical relationship between quantities.
ratio — A comparison of amounts by division.
rate — The amount of change or occurrence per unit of time or another quantity.
difference — The amount by which two values are unequal.
percentage — A proportion expressed per one hundred.
average — A representative value, often the arithmetic mean.
range — The span between the smallest and largest values.
maximum — The greatest value in a set.
minimum — The smallest value in a set.
threshold — A value at which a particular change begins or is observed.
consistent pattern — A relationship appearing repeatedly in comparable data.
exception — A case not following the general pattern.
prediction limit — A boundary beyond which available data may not justify a forecast.

8. Evaluate the quality of an investigation

A pupil who repeats a test may find a different result. Instead of changing the data to make the graph tidy, the correct step is to check the method and consider variation.

Avoid this mistake: Unexpected findings are not automatically mistakes. Record them honestly and test whether the method or conditions explain the variation.

Practice: Read a short experimental report and identify one strength, one limitation and a way to improve the test.

reliability — The consistency of results when methods are repeated appropriately.
repeatability — Ability to obtain similar results using the same method.
reproducibility — Ability to obtain comparable findings under relevant repeated conditions.
validity — How well a method actually answers the question investigated.
bias — A systematic influence that distorts observations or decisions.
measurement error — A difference between recorded and correct measurement.
instrument error — An error arising from a measuring tool or its use.
reading error — A mistake made while reading a scale or result.
parallax error — A reading error caused by viewing a scale at an angle; extension term.
anomaly — A result that stands out from the main observed pattern.
natural variation — Differences that occur even when conditions appear similar.
experimental limitation — A feature restricting the conclusion a test can support.
improvement — A change designed to make a method clearer or more reliable.
repeat check — An extra test used to see whether a finding recurs.
standardised method — A procedure kept consistent across samples or trials.
record keeping — Storing observations clearly enough for later checking.
objectivity — Assessing results without favouring a preferred outcome.
fairness — Using comparable rules and conditions in a comparison.
ethical practice — Avoiding unnecessary harm or dishonest manipulation of evidence.
safety precaution — A planned action reducing risks during an investigation.

9. Apply reasoning across Biology and Physics

PSLE Science combines topics: a plant may depend on light, a magnet may act without contact and an animal may be affected by a food-web change. Each explanation needs the correct mechanism.

Avoid this mistake: Do not replace the actual mechanism with a long list of chapter terms. Different questions require different reasons.

Practice: Take a question about a plant, a moving ball and a circuit. For each, write the mechanism that directly explains the result.

photosynthesis — The process by which green plants use light to make food.
respiration — Processes in living cells releasing energy from food.
transpiration — Loss of water vapour from plant surfaces; extension vocabulary.
condensation — Change of a gas or vapour into liquid.
evaporation — Change of liquid into gas at the exposed surface.
melting — Change of a solid into a liquid.
friction — A force opposing relative movement between touching surfaces.
gravity — The attractive force between objects with mass.
spring force — A restoring force that may act when a spring is stretched or compressed.
magnetic force — A force arising from magnetic interactions.
energy conversion — Change from one form of energy to another.
energy transfer — Movement of energy from one place or system to another.
closed circuit — A conducting route complete enough for current to flow.
open circuit — A circuit route interrupted so current cannot continue there.
series circuit — A circuit arrangement having a single main current pathway.
parallel circuit — An arrangement with several conducting branches.
adaptation — An inherited feature or behaviour that aids survival or reproduction.
food chain — A sequence of feeding relationships showing energy transfer.
decomposer — An organism breaking down dead material.
habitat — The environment in which an organism normally lives.

10. Write concise, complete scientific answers

A short answer can be excellent when it gives the correct cause, process and observed result. A long paragraph can still be wrong if it repeats the question or changes the evidence.

Avoid this mistake: Do not guarantee a particular mark from a memorised sentence frame. The question, data and syllabus determine what a complete answer must include.

Practice: Write one accurate explanation, remove irrelevant sentences and check whether the causal relationship remains clear.

complete answer — A response addressing every part of the question.
relevant detail — Information that helps answer the stated task.
irrelevant detail — Information that does not help establish the requested answer.
concise — Clear and brief without omitting necessary meaning.
specific — Focused on the particular condition, part or result.
general — Applying to many cases without identifying a particular detail.
qualified statement — A claim limited by its stated conditions.
because statement — A sentence giving a cause or scientific reason.
therefore statement — A sentence expressing a conclusion following from reasons.
causal chain — A series of connected steps from cause to outcome.
scientific vocabulary — Terms used to express observations, processes and concepts accurately.
key term — A word central to the relationship being explained.
misconception — An incorrect idea that can produce repeated errors.
self-check — A review of one’s answer for completeness and accuracy.
peer explanation — Explaining the reasoning to another learner.
error log — A record of mistakes and what caused them.
revised answer — A response changed after checking a misunderstanding.
independent response — An answer written without copying the model solution.
transfer of learning — Using an understood idea in a new situation.
concept mastery — Being able to explain and apply an idea across contexts.

Seven original worked examples with answer explanations

1. State, describe and explain are different instructions

Scenario: A torch is switched off and a patch of light disappears from the wall. State: The patch is no longer visible. Describe: When the torch was switched off, the illuminated patch disappeared. Explain: The torch stopped supplying light to that area, so the wall no longer received that illumination. The scientific action demanded by the command word changes what belongs in the answer.

2. What can a growth graph really establish?

Scenario: A chart shows that seedling A increased in height each week. Supported statement: Seedling A grew taller over the recorded period. Unsupported statement: More fertiliser must have caused the growth. Unless the study compared fertiliser conditions appropriately, the graph alone cannot establish that cause. A clear data interpretation includes the actual trend and avoids inventing missing variables.

3. Identify a fair test for evaporation

Scenario: A student wants to test whether moving air changes how quickly identical wet cloths dry. Better method: Use comparable cloths with similar initial water amounts and exposure conditions, deliberately varying the airflow. Measure the water lost or another suitable outcome over the same time. The changing factor is the airflow, while the result is the observed drying. If one cloth also sits in stronger sunlight, that could confound the comparison.

4. Interpret a broken circuit

Scenario: A bulb does not light after its switch is opened. Observation: The bulb goes out. Explanation: Opening the switch interrupts the conducting path, preventing the usual current around that route. ‘Because the bulb is off’ merely repeats the observation and does not explain the mechanism. A good response names the break in the route.

5. Compare the effects of friction on two surfaces

Scenario: Identical toy cars are launched in a comparable manner on two different surfaces, but one stops sooner. Reasoned answer: Differences in frictional interactions may contribute to different slowing behaviour. Whether the result is due to surface type depends on whether other relevant factors were adequately controlled. The pupil should not claim that a rougher surface always stops every object first, independent of conditions.

6. Explain a food-web change carefully

Scenario: A particular insect population decreases in a park. Reasoned answer: Animals that feed on those insects may have less food available, which could affect their survival or numbers. The actual outcome may also depend on alternative food sources, migration and other conditions. Use ‘may’ where evidence supports a possible effect but does not establish a certain outcome.

7. Evaluate the reliability of a measurement

Scenario: A learner records the spring extension only once and the reading differs from earlier class results. Reasoned answer: Check the scale, viewpoint, load and procedure, then take appropriately repeated readings. An unusual result may reflect measurement error or real variation. It should not be silently erased or changed to match the expected value. Correct record-keeping is part of good scientific practice.

The answer-building routine: read, locate, explain, check

Read. Underline the command word and mark the specific condition in the question. If the instruction is ‘compare’, identify the two cases. If it is ‘suggest a method’, identify the aim, apparatus and measurable result. If it says ‘explain’, prepare to supply a cause or process. The student should answer the question that was asked, not the one they hoped was asked.

Locate. Find the relevant clue in the diagram, graph or text. Read axis labels, units, arrow directions and connections. In a circuit, trace the wiring from one terminal through each component. In a food chain, follow the direction of feeding and energy transfer. In a water-cycle diagram, distinguish the movement of water from its change of state. Every diagram element has a role; missing one can reverse the explanation.

Explain. Connect the evidence to a specific scientific relationship. A useful causal sentence states the condition, the process and the result. But this is a thinking aid, not a magic exam template. Some questions ask for a direct observation, a calculation or an alternative procedure, so the answer should adapt. Be concise; scientific meaning matters more than fancy phrasing.

Check. Ask whether every part has been answered, whether the direction is correct, whether the unit is present and whether the conclusion overreaches the data. A pupil might write ‘mass increased’ when the graph actually measures volume, or claim sunlight caused a result that is only shown over time. These are repairable reading and reasoning mistakes. Correcting them helps more than copying an entire model paragraph again.

How to make Science revision calmer and more effective

Begin with one weak mechanism rather than ten general worksheets. If a child confuses observation and inference, practise that distinction on different photographs and tables before returning to a full examination page. If the issue is graph interpretation, focus on axes, units and supported trends. If the issue is open-ended vocabulary, ask the child to restate the question in plain English and then explain the scientific reason aloud before writing.

Use an error log with a reason column. For each missed question, record the topic, the student’s first wrong step and a corrected principle. Common labels include: misunderstood command word, wrong process, reversed direction, missing variable, misread graph, unsupported conclusion or incomplete explanation. Return after two days and again after a week, ideally with a new example. The goal is independent application, not memorising a repaired sentence.

Parents can also make use of safe Singapore surroundings. Evaporation after a brief shower, condensation on a chilled cup, light and shadow near a sheltered walkway, roadside plants and a battery-powered device offer real examples. The child should practise explaining what was observed. Avoid taking risks with hot liquids, electricity, unknown substances or small magnets. Photographs and diagrams are usually sufficient.

Four-week PSLE Science reasoning plan

Week 1 — Command words and observation language

Learn the first three groups and practise telling observation from inference. Read two diagrams each day and write what they show without inventing causes. Rephrase a single original question using ‘state’, ‘describe’ and ‘explain’ to see how the expected response changes. Focus on exact, short language.

Week 2 — Fair tests, variables and measurement

Study the investigation and measurement groups. Design a small safe comparison and list the changing, measured and controlled factors. Check whether each measurement has an appropriate unit. Practise reading a scale from the correct position where relevant. Record observations honestly, including awkward results.

Week 3 — Graphs, trends and uncertainty

Study the table, graph and relationship groups. Use four to six invented numerical values to draw a graph and state its actual trend. Ask which claims are supported and which need more evidence. Distinguish ‘changed together’ from ‘one definitely caused the other’. Practise alternative explanations rather than guessing an impressive-sounding mechanism.

Week 4 — Mixed scientific reasoning and error repair

Use the final three groups with mixed school questions on plants, circuits, forces, water and environmental interactions. Ask the student to explain a new example, not reproduce one sentence from memory. After completing a question, check that the answer includes all requested elements and does not conflict with the data. Review the error log and reteach only the misconceptions that remain.

PSLE Science open-ended question FAQ

Does SEAB require a particular memorised answer template?

No single memorised wording guarantees marks. The answer needs to demonstrate the correct concept, relevant evidence and the reasoning requested by the question. SEAB has highlighted that scientifically valid alternative approaches can be recognised in suitable open-ended assessment tasks. The exact marking expectations depend on the question.

Are these 200 terms official examinable vocabulary?

No. They are an eduKate editorial selection of question language, investigation terms, data-reading vocabulary and common Science concepts. The current MOE syllabus and appropriate SEAB examination information define what is assessed. Some terms here are explicitly useful for wider reading rather than P6 compulsory recall.

What is the difference between observation and inference?

An observation describes what was directly noticed or measured. An inference is a reasoned interpretation of that information. ‘The object floated’ is an observation. ‘Its density may be lower than the fluid’s density’ is an interpretation, and whether that statement is appropriate depends on the given conditions and curriculum level.

How do I teach fair-test variables?

Choose a simple question. Name what the investigator deliberately changes, what is measured and which relevant circumstances stay similar. Use a familiar example such as drying cloths under different airflow conditions. Encourage the child to explain why changing several factors at once weakens a conclusion about one cause.

How do I help a child who writes too much?

Have the child underline only the scientific statement that answers the command word, and cross out unrelated facts. A correct ‘because’ explanation may need just one or two sentences. Longer answers are necessary only when the question asks for additional reasons, comparisons, steps or evidence.

What about Foundation Science?

Foundation Science has its own examination and some different syllabus expectations. The MOE 2023 curriculum shows content differentiation, and the correct SEAB syllabus should be checked for a particular exam year. Use the reasoning routines here when relevant, but do not assume all content or technical terms apply unchanged.

Where do I find the latest examination format?

Use the SEAB PSLE official information page and the format documents for the examination year that matters. Earlier-year papers can be useful practice, but do not assume their timing, sections or mark distribution are permanently unchanged.

Read official sources and complementary eduKate material

The MOE Primary Science Teaching and Learning Syllabus describes knowledge, practices and scientific reasoning. SEAB’s 2026 explanation of thoughtful PSLE assessment design discusses the role of multiple scientifically valid approaches. For topic vocabulary, use Primary 6 Science: 200 PSLE Keywords, Forces, Energy and Adaptations; for data and experiments, Primary 3 Science Process Skills explains the earliest inquiry foundation. The Primary 6 Science Vocabulary: Processes, Evidence and Relationships offers another route into scientific explanations.

What matters most: read the evidence, choose the right concept and express the relationship accurately. Vocabulary should help a student think through the question, not disguise a gap in understanding.