Grade: Grade 5 Subject: Science Unit: Ecosystems & Energy Flow Lesson: 5 of 6 SAT: Information+Ideas ACT: Science

Claim-Evidence Writing: Ecosystems

Learn to write scientific arguments about ecosystems using the CER framework: Claim, Evidence, and Reasoning.

Learn

Scientists don't just discover facts - they also need to communicate their findings clearly. One of the most important skills in science is writing arguments that explain what you've learned. The CER framework helps you organize your scientific writing.

What is CER?

CER stands for Claim, Evidence, and Reasoning. It's a framework scientists use to communicate their conclusions based on data and observations. This same structure is used in scientific papers, lab reports, and even on standardized tests!

The CER Framework

C - Claim

What do you think?

A claim is a statement that answers the question or problem. It's your conclusion or main idea based on what you've observed or learned.

E - Evidence

What data supports it?

Evidence includes specific data, observations, or facts that support your claim. This might include numbers, measurements, or descriptions from experiments.

R - Reasoning

Why does it matter?

Reasoning explains WHY your evidence supports your claim. It connects your evidence to scientific principles and concepts.

Example: Energy Flow in Ecosystems

Question: Why are there fewer top predators than producers in an ecosystem?

Claim

There are fewer top predators than producers in an ecosystem because energy is lost at each level of the food chain.

Evidence

In a grassland ecosystem, there are approximately 10,000 kg of grass (producers), but only 1,000 kg of rabbits (primary consumers), 100 kg of foxes (secondary consumers), and just 10 kg of hawks (top predators). The energy pyramid shows that only about 10% of energy transfers from one level to the next.

Reasoning

This pattern occurs because organisms use most of the energy they consume for their own life processes like movement, growth, and reproduction. Since only 10% of energy passes to the next level, each level can support fewer and fewer organisms. That's why top predators are always the smallest population in an ecosystem - there simply isn't enough energy to support more of them.

Writing Tip: When writing your evidence, be specific! Use actual numbers, data, or detailed observations rather than vague statements like "a lot" or "many."

Practice Writing Prompt

Question: What would happen to an ecosystem if all the decomposers disappeared?

Write a CER response explaining the impact on the ecosystem.

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Practice Quiz

Test your understanding of the CER framework and ecosystem concepts.

1 Which part of a CER response explains WHY your evidence supports your claim?
A Claim
B Evidence
C Reasoning
D Conclusion
2 A student writes: "The rabbit population decreased." Which part of CER is this?
A Claim
B Evidence
C Reasoning
D Question
3 Which statement is the BEST example of a claim about ecosystems?
A The hawk ate 3 mice on Tuesday.
B Removing predators from an ecosystem will cause herbivore populations to increase.
C Energy flows from the sun to producers.
D The data table shows population changes over time.
4 Why should evidence in a CER response include specific numbers when possible?
A Numbers make the writing longer
B Specific data provides stronger, more convincing support for claims
C Teachers like to see math in science writing
D Numbers are easier to remember
5 In an energy pyramid, what percentage of energy typically transfers from one trophic level to the next?
A 100%
B 50%
C 10%
D 1%
6 Which statement would be appropriate REASONING in a CER response about food webs?
A The rabbit population was 500 in January.
B This happens because consumers depend on producers as the base of all food chains.
C Food webs are complex.
D The fox ate the rabbit.
7 What would most likely happen if a disease killed all the grass in a prairie ecosystem?
A Only the top predators would be affected
B All animals in the food web would eventually be affected
C Herbivores would start eating meat instead
D The predators would become producers
8 A complete CER response must include:
A Only a claim and evidence
B Only evidence and reasoning
C Claim, evidence, AND reasoning
D Only a claim
9 Why are decomposers essential to the cycling of energy and matter in ecosystems?
A They are the largest organisms
B They break down dead material and return nutrients to the soil
C They produce oxygen through photosynthesis
D They eat only top predators
10 What makes the difference between a weak claim and a strong claim?
A Strong claims are longer
B Strong claims are specific and can be supported with evidence
C Strong claims use bigger words
D Strong claims don't need evidence

Check Your Understanding

C = Claim

Your answer to the question - a statement that can be supported.

E = Evidence

Data, observations, or facts that support your claim.

R = Reasoning

Explanation of WHY evidence supports claim using scientific concepts.

Key Takeaways

  • CER helps you write clear, organized scientific arguments
  • Always include specific data in your evidence
  • Reasoning connects evidence to scientific principles
  • This framework is used on standardized tests like SAT and ACT

Next Steps

  • Practice writing CER responses about other science topics
  • Use CER in your lab reports and science projects
  • Complete the Unit Checkpoint to test your ecosystem knowledge