Build a claim-supporting graph
Pick what to plot and read the trend so the graph actually backs the claim you are making.
- Independent vs. dependent variable: To choose axes you must know which variable you changed (independent, x-axis) and which you measured (dependent, y-axis).
- Reading points off axes: A trend is read from how the points move across the plot, so you first need to read an (x, y) point from labeled axes.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Choose the variables that match your claim, put them on the correct axes, then read the trend and check it actually supports the claim.
A team claims algae growth rises as nitrogen rises. They measured algae count at five nitrogen levels (see the table). Which graph and trend best support their claim?
Reviewed| Nitrogen (mg/L) | Algae count |
|---|---|
| 2 | 12 |
| 4 | 20 |
| 6 | 33 |
| 8 | 41 |
| 10 | 55 |
- A.Algae count on the x-axis, nitrogen on the y-axis; the trend falls
- B.Nitrogen on the x-axis, algae count on the y-axis; the trend rises
- C.Nitrogen on the x-axis, algae count on the y-axis; the trend is flat
- D.Either axis order works; the trend is the same either way
Show the worked solution ▾
Answer: B. Nitrogen on the x-axis, algae count on the y-axis; the trend rises
- Step 1: Match axes to the claim: Nitrogen is what changes (independent, x-axis); algae count is what was measured (dependent, y-axis).
- Step 2: Read the numbers in order: As nitrogen goes 2 to 10, algae count goes 12, 20, 33, 41, 55: it climbs every step, so the trend rises.
Why it's right: Nitrogen belongs on the x-axis and algae count on the y-axis, and the counts climb as nitrogen climbs, so a rising trend supports the claim.
- A: The axes are swapped and the data rise, not fall.
- C: The counts climb steadily, so the trend is not flat.
- D: Swapping axes changes what the graph tests; axis order is not free.
Aligned to Biomedical Innovation: graphing a claim · reading level ~grade 9
- A water-quality report graphs contaminant level against sample date so the rising line is the evidence for 'pollution is getting worse.'
Fill these in as you work through the lesson.
- Trend (the overall direction the points move):
- Independent variable (the thing you change, goes on the x-axis):
- Dependent variable (the thing you measure, goes on the y-axis):
- Claim (the one-sentence answer your graph has to back up):
Put the variable you changed on the -axis and the variable you measured on the -axis, then describe the in plain words and check it matches your claim.
- A team claims 'lead in tap water rises as pipes get older.' Which variable goes on the x-axis and which on the y-axis?
- A graph of plant height over 6 days climbs steadily. Describe the trend in one sentence.
- Why does a graph with the wrong variable on the y-axis fail to support a claim, even if it is drawn neatly?
A class measures algae growth at 5 nitrogen levels (2, 4, 6, 8, 10 mg/L) and gets algae counts of 12, 20, 33, 41, 55. Decide which variable is the x-axis and which is the y-axis, then describe the trend and write a claim it supports.