Microplastics and Marine Life — Free Printable (Grade 7)

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Microplastics and Marine Life

Grade 7 NGSS SEP4, SEP6, SEP7; CCSS.WHST.6-8.1 6 steps

Name:

Date:

Period:

What to Do

Read the Investigation Question carefully.
Study the Background Information and Data Table.
Review the Key Vocabulary — use these words in your writing.
Complete each writing step. Use evidence from the data to support your answer.
In your rebuttal, explain why the Alternative Explanation is not supported by the data.
Use the checklist at the end to review your work.

Investigation Question

Are microplastics in ocean water harming marine organisms?

Background Information

Microplastics are tiny plastic particles smaller than 5 millimeters that enter
the ocean from many sources: breakdown of larger plastic waste, synthetic clothing
fibers released during washing, microbeads from personal care products, and
industrial runoff. Scientists estimate that over 14 million tons of microplastics
sit on the ocean floor, with trillions more floating in surface waters.

Marine organisms encounter microplastics constantly. Filter-feeding animals like
zooplankton, mussels, and small fish cannot distinguish microplastics from food
particles and ingest them. Microplastics can carry toxic chemicals on their
surfaces, including pesticides, heavy metals, and industrial pollutants that
adhere to plastic in seawater.

A marine biology research team conducted a controlled laboratory study to
investigate whether microplastics affect zooplankton health. They raised
populations of the copepod Acartia tonsa (a common zooplankton species) in tanks
with different concentrations of polyethylene microplastic particles (50-100
micrometers in size). Each tank started with 200 adult copepods. After 21 days,
the researchers counted the number of eggs produced per female and measured
the survival rate of offspring.

Some scientists have argued that ocean temperature changes, not microplastics,
are the primary cause of declining zooplankton populations in the wild.

Zooplankton Reproduction and Survival at Different Microplastic Concentrations

Microplastic Concentration (particles/L)	Avg Eggs per Female (21 days)	Offspring Survival Rate (%)	Adult Survival (%)
0 (control)	42	89	95
10	39	85	93
100	31	72	88
1,000	18	51	76
5,000	8	28	61

Each treatment had 3 replicate tanks of 200 copepods. Water temperature was 20°C ± 0.5°C in all tanks. Polyethylene particles were 50-100 μm diameter. Fed identical algae diet.

Alternative Explanation (for your Rebuttal)

"The decline in zooplankton reproduction is caused by rising ocean temperatures, not microplastics."

Key Vocabulary

Word	Definition
microplastics	Plastic particles smaller than 5 mm that enter the environment from degrading plastic waste, synthetic fibers, and industrial sources — too small to be filtered by most water treatment
bioaccumulation	The buildup of a substance in an organism's body over time because it is absorbed faster than it can be broken down or eliminated
zooplankton	Tiny marine animals that drift in ocean currents and form the base of marine food webs — they are eaten by fish, whales, and many other ocean animals
reproductive toxicity	When a harmful substance reduces an organism's ability to reproduce — this can include fewer offspring, lower survival of young, or developmental abnormalities
dose-response relationship	The pattern where increasing the amount of a substance causes a proportionally larger effect — a key concept in toxicology
controlled experiment	An experiment where all variables except the one being tested are kept the same, so any observed changes can be attributed to the test variable

Writing Steps

1 Examine the Evidence

Answer these questions to show you understand the data:

1. What is the investigation question asking you to explain?
2. What is the independent variable? The dependent variable?
3. What trend or pattern do you see in the data? (Be specific — use numbers.)
4. Can you think of an alternative explanation for the data? What else could cause this result?

Bullet points or short sentences are fine.

Before writing, carefully read the investigation question and analyze the data.

Scientists read data critically before forming explanations. Look for:
- Patterns and trends in the numbers
- Which variables were controlled and which were tested
- What the data shows and what it doesn't show
- What alternative explanations a skeptic might propose

Note: This step prepares you to write. It is not part of your final score.

Scoring Guidance — Step 1

Look for:

Independent variable = what was changed. Dependent variable = what was measured.
Note specific values: the highest, lowest, the difference between conditions
Think like a skeptic: could anything else explain this pattern?

Claim

Evidence

Reasoning

Rebuttal

2 Write Your Claim

Write one precise sentence that answers: Are microplastics in ocean water harming marine organisms?

Make sure your claim:
- States a specific relationship between two variables
- Uses precise scientific language
- Could be tested or proven wrong with data

A claim is one precise sentence that directly answers the investigation question.

Investigation Question: Are microplastics in ocean water harming marine organisms?

A strong claim:
- Answers the question in ONE sentence
- Is precise and measurable
- Names the direction of effect
- Is falsifiable — it could be tested or proven wrong

Scoring Guidance — Step 2

Role: claim

Target: ~20 words

Look for:

Name both variables: what was changed AND what was measured
State the direction: as X increases, Y increases/decreases
Avoid vague language: 'affected it' → name the specific effect

Name both variables: what was changed AND what was measured

State the direction: as X increases, Y increases/decreases

Avoid vague language: 'affected it' → name the specific effect

Sentence Starters

My claim is that ___ affects ___.

Based on the data, ___.

The investigation shows that ___.

Target: about 20 words

3 Cite Your Evidence

Write 2-3 sentences of evidence from the data table.

Your evidence should:
- Include specific numbers with units from the data table
- Show a comparison (highest vs. lowest, between conditions)
- Come from the investigation data, not background knowledge

Evidence is specific data from the investigation that supports your claim.

Strong evidence:
- Includes 2+ specific data points with numbers
- Comes from YOUR investigation data (not background knowledge)
- Distinguishes between primary data and background context
- Is directly relevant to your claim

Scoring Guidance — Step 3

Role: evidence

Target: ~40 words

Look for:

Use at least 2 specific numbers from the data table
Compare values: '...compared to...' or 'while...' or 'In contrast...'
Include units (cm, °C, mg/L, etc.)

Data Reference (Avg Eggs per Female (21 days)) 0 (control): 4210: 39100: 311,000: 185,000: 8

Use at least 2 specific numbers from the data table

Compare values: '...compared to...' or 'while...' or 'In contrast...

Include units (cm, °C, mg/L, etc.)

Sentence Starters

The data table shows that when ___, ___.

Specifically, the measurement of ___ was ___.

Two data points that support my claim are ___ and ___.

Target: about 40 words

4 Write Your Reasoning

Write 3-4 sentences explaining WHY your evidence supports your claim.

Your reasoning MUST include:
- A named scientific principle (e.g., natural selection, Newton's third law, photosynthesis)
- An explanation of the MECHANISM: HOW does this principle cause your result?
- Language like "This demonstrates..." or "According to [principle]..."

Reasoning is the scientific explanation that connects your evidence to your claim.

Reasoning is NOT a repeat of your evidence. Reasoning MUST:
- Name a scientific principle or concept
- Explain the MECHANISM — HOW or WHY the principle causes the observed result
- Use language like "This demonstrates..." or "According to..."

Scoring Guidance — Step 4

Role: reasoning

Target: ~40 words

Look for:

Name the scientific principle: 'This demonstrates [concept]...'
Explain the mechanism: not just WHAT but HOW/WHY
Check: Did you actually explain the science? Or just restate the data?

Name the scientific principle: 'This demonstrates [concept]...

Explain the mechanism: not just WHAT but HOW/WHY

Check: Did you actually explain the science? Or just restate the data?

Sentence Starters

This supports my claim because the principle of ___ explains ___.

The scientific mechanism behind this is ___.

Therefore, when ___, ___ because ___.

Target: about 40 words

5 Write Your Rebuttal

Write 3-4 sentences for your rebuttal.

Your rebuttal should:
1. Name the most plausible alternative explanation for the data
2. Explain why someone might believe this alternative
3. Use evidence to explain why your claim is still better supported

Think: What is the strongest counter-argument someone could make? How does the data rule it out?

A rebuttal is what separates a strong scientific argument from a weak one.

Scientists must be honest about alternative explanations — and then explain why those alternatives are less supported by the evidence.

A strong rebuttal:
- Acknowledges a plausible alternative explanation (what a skeptic might say)
- Explains specifically WHY the evidence still supports your original claim
- Uses evidence to show why the alternative is weaker
- Does NOT just say "some people might disagree, but I'm right"

Weak rebuttal: "Some people might think that [alternative], but my claim is correct."
Strong rebuttal: "One alternative explanation is that [specific alternative], because [reason it seems plausible]. However, the data shows [specific data point] which rules this out because [scientific reasoning]."

Scoring Guidance — Step 5

Role: rebuttal

Target: ~50 words

Look for:

Start with: 'One alternative explanation is...' or 'A skeptic might argue that...'
Name the specific alternative: don't be vague
Use evidence to refute it: 'However, the data shows [specific numbers]...'
Explain WHY your data rules out the alternative

Start with: 'One alternative explanation is...' or 'A skeptic might argue that...

Name the specific alternative: don't be vague

Use evidence to refute it: 'However, the data shows [specific numbers]...

Explain WHY your data rules out the alternative

Sentence Starters

An alternative explanation is ___.

Some might argue ___; however, the data shows ___.

While ___ could explain this, the evidence more strongly indicates ___.

Target: about 50 words

6 Write Your Complete CERR Paragraph

Write your complete CERR paragraph (6-9 sentences).

Use your claim, evidence, reasoning, and rebuttal from previous steps.
Improve them as you write — aim for precision and flow.

Checklist before submitting:
- [ ] Claim: precise sentence answering the investigation question
- [ ] Evidence: 2+ specific data points with numbers
- [ ] Reasoning: named scientific principle + mechanism explanation
- [ ] Rebuttal: named alternative + evidence-based refutation
- [ ] Flow: transitions connect all four parts

Now assemble your entire argument into one polished paragraph.

Your scaffold boxes show what you've written — use those as your starting point and improve them.

A complete CERR paragraph for Grade 6-8:
- Starts with a precise claim (1 sentence)
- Provides 2+ pieces of evidence with specific data
- Explains reasoning with a named scientific principle and mechanism
- Acknowledges and substantively rebuts the best alternative explanation
- Flows with appropriate transitions
- Is 6-9 sentences

Transitions for CERR: "Furthermore," "This demonstrates," "However, a skeptic might argue," "The data refutes this because," "Therefore,"

Scoring Guidance — Step 6

Role: complete CERR paragraph

Target: ~130 words

Look for:

Claim → Evidence → Reasoning → Rebuttal is the standard CERR structure
Use transitions: 'This demonstrates...' → 'However, one alternative explanation...' → 'The data refutes this...'
Your rebuttal should feel like the strongest counter-argument you can imagine — then knock it down

Data Reference (Avg Eggs per Female (21 days)) 0 (control): 4210: 39100: 311,000: 185,000: 8

Claim → Evidence → Reasoning → Rebuttal is the standard CERR structure

Use transitions: 'This demonstrates...' → 'However, one alternative explanation...' → 'The data refutes this...

Your rebuttal should feel like the strongest counter-argument you can imagine — then knock it down

Claim + Evidence + Reasoning + Rebuttal = Complete Paragraph

Sentence Starters

My claim is ___. The evidence shows ___. The principle of ___ explains this.

Some might argue ___; however, the data more strongly supports my claim because ___.

Target: about 130 words

Self-Check Rubric

Criteria	●●●●● 5 — Advanced	●●●●○ 4 — Proficient	●●●○○ 3 — Developing	●●○○○ 2 — Emerging	●○○○○ 1 — Beginning
Claim	Clear, specific claim that directly answers the question	Clear claim that answers the question	Claim present but vague or partially answers question	Claim unclear or off-topic	No claim or unrelated
Evidence	Multiple specific data points cited accurately	Specific data cited accurately	Some data referenced but vague	Little or no data cited	No evidence from data
Reasoning	Explains WHY data supports claim using science concepts	Explains connection between evidence and claim	Some explanation but gaps in logic	Weak or missing explanation	No reasoning
Rebuttal	Addresses alternative and explains why data disproves it	Addresses alternative with evidence	Mentions alternative but weak counter	Does not address alternative	No rebuttal

Before You Turn In

I completed the planning step

I wrote my claim

My claim is about 20 words

I wrote my evidence

My evidence is about 40 words

I wrote my reasoning

My reasoning is about 40 words

I wrote my rebuttal

My rebuttal is about 50 words

I wrote my complete CERR paragraph

My complete CERR paragraph is about 130 words

I re-read my writing and fixed any spelling or grammar mistakes

I am proud of this work

Reflection

What was the hardest part of this assignment? What would you do differently next time?

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