Claim-Evidence Writing
Learning Objectives
In this lesson, you will:
- Write scientific claims based on ecological data
- Support claims with specific evidence
- Provide scientific reasoning connecting evidence to claims
- Practice the CER (Claim-Evidence-Reasoning) framework
Practice Quiz
Practice writing scientific arguments. Click to reveal each answer.
Question 1: Data shows deer population increased from 50 to 400 after wolves were removed. Write a claim about this relationship.
Sample Claim: The removal of wolves as a top predator led to an increase in the deer population due to reduced predation pressure.
Explanation: Good claims state a relationship between variables and provide a mechanism (why it happened).
Question 2: What makes evidence strong in a scientific argument?
Answer: Strong evidence is: specific (includes data and numbers), relevant to the claim, from a reliable source, reproducible, and sufficient in quantity.
Explanation: "The population increased" is weak. "The population increased from 50 to 400 individuals (an 8x increase) over 10 years" is strong evidence.
Question 3: Write a reasoning statement connecting this evidence to a claim about biodiversity: "When the invasive species was introduced, native species declined from 15 to 3."
Sample Reasoning: Invasive species often outcompete natives for resources and may lack natural predators in the new environment. The dramatic decline from 15 to 3 native species (80% loss) demonstrates the invasive species displaced native organisms, reducing biodiversity.
Explanation: Reasoning uses scientific principles to explain WHY the evidence supports the claim.
Question 4: Identify the error: "Pollution is bad because the river looks dirty."
Error: This uses qualitative observation ("looks dirty") instead of measurable data. It also lacks scientific reasoning.
Improved: "Pollution has degraded river health as evidenced by dissolved oxygen levels dropping from 8 mg/L to 2 mg/L, which is below the 5 mg/L threshold required for most fish survival."
Question 5: How do you address alternative explanations in scientific writing?
Answer: Acknowledge other possible explanations, then explain why your evidence better supports your claim, or note what additional evidence would be needed to rule out alternatives.
Explanation: Good science considers competing hypotheses. Addressing them strengthens your argument.
Question 6: Write a CER paragraph: Graph shows increasing CO2 correlates with decreasing pH in ocean water over 50 years.
Sample CER: Claim: Ocean acidification is occurring due to increased atmospheric CO2 absorption. Evidence: Over the past 50 years, ocean pH has decreased from 8.2 to 8.1 as CO2 levels rose from 320 to 420 ppm. Reasoning: When CO2 dissolves in seawater, it forms carbonic acid, lowering pH. This chemical process directly links rising atmospheric CO2 to ocean acidification.
Question 7: Why is correlation not sufficient to prove causation in ecology?
Answer: Two things may change together due to a third variable (confounding factor). Without controlled experiments or mechanistic understanding, we cannot prove one variable causes change in another.
Explanation: Example: Ice cream sales and drowning rates both increase in summer, but ice cream doesn't cause drowning - both are caused by hot weather.
Question 8: How should uncertainty be expressed in scientific claims?
Answer: Use hedging language ("suggests," "indicates," "likely") when appropriate. Report confidence intervals or ranges. Acknowledge limitations of data or methods.
Explanation: "The data proves..." is too strong. "The evidence suggests..." or "These results indicate..." shows appropriate scientific caution.
Question 9: Evaluate this evidence: "Everyone knows deforestation is harmful." Is this acceptable scientific evidence?
Answer: No. This is an appeal to common knowledge, not evidence. Scientific arguments require data, measurements, or documented observations.
Improved: "Deforestation removed 4.2 million hectares of Amazon rainforest in 2020, releasing an estimated 2.8 billion tonnes of CO2 and displacing approximately 10,000 species."
Question 10: Write a complete CER about the 10% energy rule in food chains.
Sample CER: Claim: Energy transfer between trophic levels is inefficient, limiting food chain length. Evidence: Studies show that only approximately 10% of energy at one trophic level transfers to the next; for example, if producers contain 10,000 kcal, primary consumers receive about 1,000 kcal, and secondary consumers about 100 kcal. Reasoning: Most energy (90%) is lost as heat during metabolic processes like respiration. This inefficiency means there's insufficient energy to support many trophic levels, which explains why most food chains have only 4-5 levels.
Next Steps
- Practice writing CER paragraphs for other ecology topics
- Review scientific reasoning patterns
- Complete the unit checkpoint when ready