CER Writing: Ecosystems
What is CER?
Scientists explain their thinking using CER: Claim, Evidence, and Reasoning.
The CER Framework
- Claim: Your answer to the question (1 sentence)
- Evidence: Data or facts that support your claim (2-3 pieces)
- Reasoning: Explain HOW your evidence supports your claim
Example CER
Question: Why do ecosystems need producers?
Claim: Ecosystems need producers because they are the only organisms that can capture energy from the sun.
Evidence: Producers like plants use photosynthesis to make food from sunlight. All consumers must eat other organisms to get energy. In a food chain, producers are always at the bottom.
Reasoning: This shows that producers are essential because without them, there would be no way for energy to enter the food chain. Consumers cannot make their own food, so they depend on producers. If producers disappeared, all the consumers would eventually die because they would have no source of energy.
Practice Questions
1. Which is the best CLAIM for the question "What happens when a food chain loses its top predator?"
A) Food chains are interesting
B) When a food chain loses its top predator, the population of prey animals increases
C) Top predators eat meat
D) I like animals
Answer
B) - This claim directly answers the question with a specific, testable statement.
2. Which is the best EVIDENCE for the claim "Decomposers are important for ecosystems"?
A) Decomposers are gross
B) Decomposers break down dead matter and return nutrients to the soil
C) I saw a mushroom once
D) Decomposers are living things
Answer
B) - This provides specific factual information that supports the claim.
3. What makes good REASONING in a CER?
A) Restating the claim
B) Adding more evidence
C) Explaining how the evidence supports the claim
D) Changing the topic
Answer
C) - Reasoning connects your evidence to your claim and explains the "why."
4. A student writes: "Plants are producers. Plants make their own food." What is missing?
A) Claim
B) Evidence
C) Reasoning
D) Nothing is missing
Answer
C) Reasoning - The student needs to explain WHY making their own food makes plants important producers.
5. Which question would be good for a CER about ecosystems?
A) What color are plants?
B) Why are food chains important for ecosystems?
C) How many plants are there?
D) What is a plant?
Answer
B) - This question requires explanation and reasoning, not just a simple fact.
6. How many pieces of evidence should a good CER have?
A) 0
B) 1
C) 2-3
D) 10 or more
Answer
C) 2-3 - Multiple pieces of evidence make your argument stronger.
7. "This shows that..." is a good way to start which part of CER?
A) Claim
B) Evidence
C) Reasoning
D) Title
Answer
C) Reasoning - "This shows that..." helps explain how your evidence connects to your claim.
8. What should come FIRST in a CER?
A) Evidence
B) Reasoning
C) Conclusion
D) Claim
Answer
D) Claim - Start with your answer (claim), then support it with evidence and reasoning.
9. Which word helps introduce evidence?
A) "I think..."
B) "For example..."
C) "Maybe..."
D) "I wonder..."
Answer
B) "For example..." - This introduces specific facts or data that support your claim.
10. Why is CER important for scientists?
A) It makes writing longer
B) It helps organize and communicate scientific thinking clearly
C) It's required by law
D) It's the only way to write
Answer
B) - CER helps scientists explain their findings in a clear, logical way that others can understand and evaluate.
Your Turn!
Write your own CER for this question:
"Why are there more producers than consumers in most ecosystems?"
Use this framework:
- Claim: There are more producers than consumers because...
- Evidence: (Give 2-3 facts from what you learned)
- Reasoning: This shows that...
Next Steps
- Practice writing CERs for other science questions
- Have a partner check your CER for all three parts
- Continue to the Unit Checkpoint