Natural Materials and Water Filtration — Free Printable (Grade 7)

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Natural Materials and Water Filtration

Grade 7 NGSS SEP4, SEP6, SEP7; CCSS.WHST.6-8.1, WHST.6-8.2 5 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.
Use the checklist at the end to review your work.

Investigation Question

Which natural material is most effective at filtering sediment and impurities from dirty water?

Background Information

In nature, water is filtered as it passes through layers of soil, sand, and rock
on its way to underground aquifers. This natural filtration removes sediment,
some bacteria, and dissolved substances, which is why groundwater is often cleaner
than surface water.

Different materials filter water differently. Some trap large particles on the
surface, while others attract and hold dissolved impurities. Scientists measure
water clarity using turbidity — a measurement in Nephelometric Turbidity Units
(NTU). Lower NTU means clearer water.

In this investigation, students poured the same muddy water (150 NTU) through
columns packed with different natural materials and measured the turbidity of the
water that came out the bottom.

Water Turbidity After Filtration Through Natural Materials

Filter Material	Turbidity After Filtration (NTU)	Percent Reduction
Activated charcoal	8	95%
Fine sand	22	85%
Cotton fiber	35	77%
Gravel	98	35%
Clay pellets	61	59%
Unfiltered (control)	150	0%

Starting turbidity: 150 NTU. Same volume (500 mL) poured through each column. Average of 3 trials.

Key Vocabulary

Word	Definition
turbidity	A measure of how cloudy or murky water is — higher turbidity means more particles are suspended in the water
filtration	The process of passing a liquid through a material that traps particles and impurities, producing cleaner water
aquifer	An underground layer of rock or sediment that holds groundwater — natural filtration cleans water before it reaches aquifers
sediment	Tiny particles of soil, sand, or organic matter suspended in water that make it cloudy
adsorption	The process by which particles stick to the surface of a material — activated charcoal has a huge surface area for adsorption

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. What do you think the data is showing? (Your prediction before writing.)

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

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.
Look for a pattern: as X increases, does Y increase or decrease?
Note specific values: the highest, the lowest, the difference

Claim

Evidence

Reasoning

2 Write Your Claim

Write one precise sentence that answers: Which natural material is most effective at filtering sediment and impurities from dirty water?

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: Which natural material is most effective at filtering sediment and impurities from dirty water?

At this grade level, a strong claim:
- Answers the question in ONE sentence
- Is precise and measurable (not vague)
- Names the direction of effect (more/less/faster/slower)
- Is falsifiable — it could be proven wrong with different data

Strong claim: "As [independent variable] increases, [dependent variable] also increases."
Weak claim: "The experiment showed that [topic] has an effect."

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, before vs. after)
- Come from the investigation data, not background knowledge

Check: Can you find your numbers in the data table? If yes, it's evidence. If not, it might be background knowledge.

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

At this grade level, strong evidence:
- Includes 2 or more 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

Primary data: Numbers or measurements from your data table.
Background knowledge: General science facts you already knew.

"The plant grew taller" is observation. "The plant in direct sunlight grew 22cm in two weeks" is evidence.

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.)
Don't cite background facts here — save those for reasoning

Data Reference (Turbidity After Filtration (NTU)) Activated charcoal: 8Fine sand: 22Cotton fiber: 35Gravel: 98Clay pellets: 61Unfiltered (control): 150

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.)

Don't cite background facts here — save those for reasoning

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 or concept (e.g., photosynthesis, Newton's third law, natural selection)
- An explanation of the MECHANISM: HOW or WHY does this concept explain your result?
- Language like "This demonstrates..." or "According to [principle]..." or "Because of [concept]..."

The test: If you removed the evidence numbers and the reasoning still made sense explaining the science, you're doing it right.

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

This is the hardest part of CER — and the most important. Reasoning is NOT:
- A repeat of your evidence
- A description of what happened
- "This proves my claim is correct"

Reasoning IS:
- A named scientific principle or concept that explains WHY
- An explanation of the MECHANISM — how or why the data shows what it shows
- The "because" that connects evidence → claim

Example (weak): "This proves that plants need more light to grow."
Example (strong): "This demonstrates the principle of photosynthesis. Plants use light energy to convert carbon dioxide and water into glucose for growth. With more light available, the plant can perform more photosynthesis, producing more glucose, which directly increases growth rate."

Scoring Guidance — Step 4

Role: reasoning

Target: ~40 words

Look for:

Name the scientific principle: '...demonstrates [concept]...'
Explain the mechanism: not just WHAT but HOW or WHY
Try: 'According to [principle], [mechanism explanation]. This means that...'
Check: Did you actually explain the science? Or just restate the data?

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

Explain the mechanism: not just WHAT but HOW or WHY

Try: 'According to [principle], [mechanism explanation]. This means that...

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 Complete CER Paragraph

Write your complete CER paragraph (5-8 sentences).

Use your claim, evidence, and reasoning from the previous steps.
Improve them as you write — make your paragraph clear, precise, and well-connected.

Checklist before submitting:
- [ ] Claim: one precise sentence answering the investigation question
- [ ] Evidence: 2+ specific data points with numbers
- [ ] Reasoning: named scientific principle + mechanism explanation
- [ ] Flow: transitions connect the three parts

Now assemble everything into one polished paragraph.

Your scaffold boxes show what you've written. Use those as your starting point — improve and connect them into flowing prose.

A complete CER paragraph for Grade 6-8:
- Starts with a precise claim (1 sentence)
- Provides 2+ pieces of evidence with specific data
- Explains the reasoning with a named scientific principle and mechanism
- Flows smoothly — uses transitions like "Furthermore," "This demonstrates," "According to..."
- Is 5-8 sentences

Scoring Guidance — Step 5

Role: complete CER paragraph

Target: ~100 words

Look for:

Start with your claim sentence
Add your evidence: 'For example, the data shows that...'
Transition to reasoning: 'This demonstrates [principle]...'
End by connecting the reasoning back to your claim

Data Reference (Turbidity After Filtration (NTU)) Activated charcoal: 8Fine sand: 22Cotton fiber: 35Gravel: 98Clay pellets: 61Unfiltered (control): 150

Start with your claim sentence

Add your evidence: 'For example, the data shows that...

Transition to reasoning: 'This demonstrates [principle]...

End by connecting the reasoning back to your claim

Claim + Evidence + Reasoning = Complete Paragraph

Sentence Starters

My claim is ___. The evidence is ___. This supports my claim because ___.

Based on the data, ___, which shows ___. This makes sense because ___.

Target: about 100 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

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 complete CER paragraph

My complete CER paragraph is about 100 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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