Math problem set Grade 8 Science

Thistlebrook Creek: Water Temperature and Oxygen Scatter Plot

A grade 8 science problem set where students scatter-plot creek temperature and dissolved oxygen, fit a trend line, and predict when oxygen drops below the fish limit.

Grade: Grade 8
Subject: Science
Material: Math problem set
Time: 45 min
Prep: No prep
Materials: Graph paper, Ruler, Calculator

Standards

8.SP.A.1 Common Core Math

Construct and interpret scatter plots for bivariate measurement data to investigate patterns of association between two quantities, describing clustering, outliers, and positive, negative, linear, or nonlinear association.

How this material aligns: Problems 1 through 3 construct and interpret a scatter plot of temperature versus dissolved oxygen, describing the negative, roughly linear association and identifying an outlier.

All materials for 8.SP.A.1 →

8.SP.A.2 Common Core Math

Know that straight lines are widely used to model relationships between two quantitative variables. For scatter plots that suggest a linear association, informally fit a straight line and assess the model fit by judging the closeness of the data points to the line.

How this material aligns: Problems 4 through 7 informally fit a straight line to the data, estimate its slope, and judge how closely the plotted points follow that line.

All materials for 8.SP.A.2 →

MS-LS2-4 NGSS

Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.

How this material aligns: Items 2, 5, and 8 build an argument from the eight days of readings that warmer creek water carries less dissolved oxygen, and that a hot spell would push oxygen under what the creek's fish need.

All materials for MS-LS2-4 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will construct a scatter plot and describe the association between two water-quality variables.
Students will fit a trend line, estimate its slope, and use it to predict a value beyond the data.

Vocabulary

Key words: scatter plot, association, trend line, outlier

Teacher overview

A volunteer monitoring the fictional Thistlebrook Creek records water temperature and dissolved oxygen on eight summer days, because warmer water holds less oxygen and low oxygen stresses fish. This problem set has students plot the data, describe the pattern, fit a trend line by eye, and use it to predict when oxygen would fall below the 5 mg/L that most fish need. A common misconception the set is built to correct is the belief that a best-fit line must pass through every data point; a good trend line comes close to the points overall while ignoring a single outlier.

Thistlebrook Creek: Water Temperature and Oxygen Scatter Plot — Grade 8 Science

Name: ____________________________ Date: ______________

Problems

Suppose the readings below come from the fictional Thistlebrook Creek. Fish generally need dissolved oxygen above 5 mg/L.

Water temperature (°C)	Dissolved oxygen (mg/L)
12	10.1
14	9.5
16	9.6
18	8.3
20	7.7
22	7.1
24	6.5
26	5.9

Construct a scatter plot with temperature on the horizontal axis and dissolved oxygen on the vertical axis. Describe the association you see.
As water temperature increases, does dissolved oxygen tend to increase or decrease?
One point sits farther from the overall pattern than the others. Name that point and state whether its oxygen is higher or lower than the trend.
Ignoring the outlier, draw a straight trend line through the points and estimate its slope in mg/L per °C. Use the readings at 12 °C and 26 °C to help.
Interpret your slope in the context of the creek.
Use your trend line to predict the dissolved oxygen at 30 °C.
Using your trend line, at about what temperature does dissolved oxygen fall to 5 mg/L?
Based on the pattern, explain what a stretch of hot summer days would likely do to the creek's oxygen and to its fish.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: Negative, roughly linear. The points fall from upper left to lower right, so as temperature rises, dissolved oxygen drops in a nearly straight-line pattern.
Answer: Decrease. Higher water temperatures line up with lower dissolved-oxygen readings throughout the table.
Answer: The point at 16 °C, 9.6 mg/L. Its oxygen is higher than the downward trend, which near 16 °C would sit closer to 8.9 mg/L.
Answer: -0.3 mg/L per °C. From (12, 10.1) to (26, 5.9), the oxygen changes by 5.9 − 10.1 = −4.2 over 26 − 12 = 14 degrees, and −4.2 ÷ 14 = −0.3 mg/L per °C.
Answer: Each 1 °C rise in water temperature lowers dissolved oxygen by about 0.3 mg/L, so warmer water carries steadily less oxygen for fish.
Answer: 4.7 mg/L. Using DO = −0.3 × temperature + 13.7, DO = −0.3 × 30 + 13.7 = −9 + 13.7 = 4.7 mg/L (accept roughly 4.5 to 5).
Answer: 29 °C. Setting −0.3 × temperature + 13.7 = 5 gives 0.3 × temperature = 8.7, so temperature = 29 °C.
Answer: Hot days would raise the water temperature, which lowers dissolved oxygen along the trend, so above about 29 °C the oxygen would drop under 5 mg/L and the fish would be stressed or begin to die.

Differentiation

Support

Provide pre-labeled and scaled axes so students plot points without setting up the grid, and mark the 5 mg/L line on the graph in advance. Give the trend-line equation DO = −0.3 × temperature + 13.7 for students who need it to attempt problems 6 and 7.

Extension

Ask students to compute how far each of the eight readings sits above or below the line DO = −0.3 × temperature + 13.7, add up the sizes of those gaps, and use the total to argue how well the line fits.

ELL supports

Pre-teach "association," "trend line," "slope," and "outlier" with a simple sketch showing points that rise, points that fall, and one stray point. Allow students to answer problems 5 and 8 with a labeled arrow on the graph plus a short phrase.