Claim-Evidence Writing
Learning Objectives
Scientific writing requires clear claims supported by evidence and reasoning. In this lesson, you will practice the CER (Claim-Evidence-Reasoning) framework.
- Write clear scientific claims
- Support claims with specific evidence from data or observations
- Explain reasoning that connects evidence to claims
- Evaluate the strength of scientific arguments
The CER Framework
- Claim: A statement that answers a scientific question
- Evidence: Scientific data or observations that support the claim
- Reasoning: Explanation of how the evidence supports the claim using scientific principles
Example CER Response
Question: Why do muscle cells have more mitochondria than skin cells?
Claim: Muscle cells contain more mitochondria than skin cells because they require more ATP to function.
Evidence: Electron microscope observations show that muscle cells contain approximately 2,000 mitochondria per cell, while skin cells contain only about 200-300 mitochondria. Additionally, studies show that muscle cells consume 10 times more ATP during activity than skin cells.
Reasoning: Mitochondria are the organelles responsible for producing ATP through cellular respiration. Muscle cells must constantly contract and relax, which requires large amounts of ATP. The higher number of mitochondria allows muscle cells to produce the ATP needed for their high energy demands. Skin cells, which primarily provide protection and do not contract, have lower energy requirements and therefore need fewer mitochondria.
Practice Quiz
Test your understanding of claim-evidence writing with these 10 questions. Click on each question to reveal the answer.
1. What is the purpose of a claim in scientific writing?
Answer: A claim is a statement that directly answers a scientific question. It should be specific, testable, and based on evidence.
2. Which of the following is the best claim? A) Cells are important. B) Mitochondria produce ATP through cellular respiration. C) I think cells are cool.
Answer: B) "Mitochondria produce ATP through cellular respiration" is the best claim because it is specific, factual, and can be supported with evidence.
3. What type of evidence would best support a claim about cellular respiration rates?
Answer: Quantitative data such as measurements of CO2 production, O2 consumption, or ATP production rates under different conditions would provide strong evidence.
4. Write a claim to answer this question: What happens to plant cells in a hypertonic solution?
Answer: Plant cells in a hypertonic solution will undergo plasmolysis as water moves out of the cell by osmosis, causing the cell membrane to pull away from the cell wall.
5. What is the role of reasoning in a CER response?
Answer: Reasoning explains WHY the evidence supports the claim by connecting the evidence to scientific principles and concepts. It shows understanding of the underlying science.
6. A student writes: "The cell has mitochondria." Is this a strong or weak claim? Why?
Answer: This is a weak claim because it is too vague and doesn't answer a specific question. A stronger claim would explain what the mitochondria do or why they are significant.
7. What makes evidence "strong" in scientific writing?
Answer: Strong evidence is specific, quantitative when possible, comes from reliable sources or experiments, is relevant to the claim, and can be verified or replicated.
8. Write appropriate evidence for this claim: "Cellular respiration is more efficient than fermentation."
Answer: Evidence: Cellular respiration produces 36-38 ATP molecules per glucose molecule, while fermentation produces only 2 ATP molecules per glucose molecule.
9. Why is it important to include reasoning and not just evidence in scientific writing?
Answer: Reasoning demonstrates understanding of scientific concepts and explains the connection between evidence and claims. Without reasoning, a reader may not understand why the evidence supports the claim.
10. Identify the claim, evidence, and reasoning: "The rough ER is involved in protein production because ribosomes are attached to it. Ribosomes are the site of protein synthesis, and their presence on the rough ER indicates that proteins are being made there."
Answer:
- Claim: The rough ER is involved in protein production
- Evidence: Ribosomes are attached to it
- Reasoning: Ribosomes are the site of protein synthesis, and their presence on the rough ER indicates that proteins are being made there
Next Steps
- Practice writing CER responses for other cell biology topics
- Review your previous work and add reasoning where needed
- Continue to the Unit Checkpoint to assess your overall understanding