Science Open Ended 2-Mark Questions


Science Open Ended 2-Mark Questions

How PSLE Science Papers Are Marked

  • Each question is assigned to a specific team of markers.
  • Markers are briefed on acceptable answers before marking starts.
  • Acceptable answers include various valid phrasings that show understanding.
  • Scripts come from all schools, so markers expect diverse wording.
  • All scripts are digitally scanned and marked on-screen.

❓ What If a New but Valid Answer Appears?

  • The marker flags the new answer to their team manager.
  • The manager discusses the answer with all other managers for that question.
  • If all agree, it’s added to the official list of accepted answers.
  • Teams are updated, and past scripts are re-marked if needed.

Types of 2-Mark Questions

There are 2 types of 2-mark open-ended questions: Process questions and Claim, Evidence, Reason (CER) questions.

  • Process questions focus on scientific processes. For example: “How does a plant make food?” or “How is oxygen transported to all parts of the body?”
  • Claim, Evidence, Reason (CER) questions require you to make a claim, support it with evidence from the question, and explain the scientific reason behind it.

CER Scoring Breakdown

Scenario 1 Scenario 2 Scenario 3 Scenario 4 Scenario 5
Claim ✔ ✘ ✔ ✔ ✔
Evidence ✘ ✔ ✘ ✔ ✔
Reason ✘ ✔ ✔ ✘ ✔
Marks 0 0 1 1 2

Example of a Process Question

Calvin conducted an experiment to find out where water droplets would form on two identical glasses of milk at different temperatures as shown. He placed the two glasses of milk on the table in a room at 30°C for 10 minutes.


Experiment setup with two glasses of milk

(a) Predict specifically where the water droplets would form in both set-ups after 10 minutes. [1]

  • (i) Set-up A: Outside the glass
  • (ii) Set-up B: Under the metal cover

(b) Explain how the water droplets are formed in set-up B. [2]

Type: Process Question

Answer: Water in the hot milk evaporates into water vapour. The water vapour loses heat to the cooler metal cover and condenses into water droplets.

How to Score for Process Questions

  • Remember the process names (e.g., evaporation, condensation, respiration, gaseous exchange).
  • Use comparative words when needed:
    • More / Less
    • Most / Least
  • If you don’t know how to do the question, identify the topic being tested and write out the relevant keywords/phrases for that topic.

Example of a CER Question

Niharika set up an experiment next to an open window using three similar types of plants as shown. The flasks were filled with the same volume of water at the start of the experiment.


Experiment setup with three plants in flasks

Predict in which set-up, X or Y, will there be a greater decrease in the volume of water. Explain your answer. [2]

Claim: Set-up X.

Evidence: X has more leaves than Y.

Reason: More leaves lead to a higher rate of photosynthesis. A higher rate of photosynthesis means more water is absorbed by the roots, causing a greater decrease in water volume.

How to Score for CER Questions

  • Write out the letters “C:”, “E:”, and “R:” in your answer to remind yourself to fill in all 3 parts.
  • Evidence: Write out exactly what you see in the question/diagram/table.
  • Reason: Use the relevant Science keywords and concepts.
  • Use relationship words like “increase” and “decrease” to show cause and effect.