On Monday, the classroom aquarium had clear water and only a small amount of algae. By Friday, thick green algae covered much of the glass.
No one saw what caused the change, but students recorded information about the aquarium each day.
Examine the Evidence
| Day | Light Each Day | Water Temperature | Nitrate Level | Amount of Algae |
|---|---|---|---|---|
| Monday | 8 hours | 22°C | 5 ppm | Very little |
| Tuesday | 8 hours | 22°C | 5 ppm | Very little |
| Wednesday | 8 hours | 22°C | 24 ppm | Small patches |
| Thursday | 8 hours | 22°C | 23 ppm | Several patches |
| Friday | 8 hours | 22°C | 21 ppm | Thick growth |
The Science Question
Which change most likely caused the rapid algae growth?
Write a response containing at least five complete sentences.
Your response must:
- Make a clear claim identifying the most likely cause.
- Include at least two specific pieces of evidence from the table.
- Explain why the algae did not appear immediately after the change.
- Identify one variable that probably did not cause the algae growth.
- Explain why the evidence supports your conclusion.
You may begin with:
The rapid algae growth was most likely caused by…
Think Before You Write
Ask yourself:
- Which measurement changed before the algae began increasing?
- Which conditions remained constant?
- Why might a living organism need time to respond to a change?
- Does the evidence prove the cause, or does it identify the best-supported explanation?
- What additional information would make your conclusion stronger?
Post Your Response
Post your five-sentence explanation in the comments.
Use only your first name and class period. Do not include your last name, email address, or other personal information.
After posting, read one classmate’s explanation and respond with one of these sentence starters:
- The strongest evidence in your response is…
- I reached the same conclusion because…
- One variable your explanation rules out is…
- Another piece of evidence you could include is…
- We could test this explanation by…
Your goal is not simply to guess the cause. Your goal is to build the explanation that is best supported by the available evidence.
When you’re finished, check out the rest of our blog for more tips, ideas, and activities to help you learn and grow. Be sure to follow our classroom Instagram page for behind-the-scenes moments, project highlights, and fun updates. Let’s work together to make learning fun, exciting, and something you look forward to every day!
