Worksheet Grade 7 Science

Ormsby Brook Dissolved Oxygen: A Grade 7 Fish Habitat Worksheet

A grade 7 science worksheet where students read dissolved-oxygen and temperature data from a cold-water stream and find when the water drops below the level fish need.

Grade: Grade 7
Subject: Science
Material: Worksheet
Time: 30 min
Prep: No prep
Materials: None

Standards

MS-LS2-1 NGSS

Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem.

How this material aligns: Items 3, 5, 6, and 8 have students interpret dissolved-oxygen data to show how a resource shortage affects whether fish can survive in the stream.

All materials for MS-LS2-1 →

7.RP.A.3 Common Core Math

Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.

How this material aligns: Item 7 asks students to compute the percent decrease in dissolved oxygen between two readings, the multistep percent reasoning this standard names.

All materials for 7.RP.A.3 →

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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 read dissolved-oxygen and temperature data from a data table.
Students will describe the relationship between water temperature and dissolved oxygen.
Students will decide when the stream falls below the oxygen level fish need.

Vocabulary

Dissolved oxygen: Dissolved oxygen is the oxygen gas mixed into water that fish and other underwater animals breathe. Cold, moving water holds more oxygen than warm, still water.

Also: milligrams per liter, cold-water stream, aquatic

Teacher overview

Fish and other stream animals breathe oxygen that is dissolved in the water. Most fish in a cold-water stream need dissolved oxygen to stay above 5 mg/L, and cold water holds more oxygen than warm water. This worksheet gives students one day of readings from a stream and asks them to find the pattern between temperature and oxygen and to spot when the water becomes unsafe for fish. In real streams, plants and algae also add oxygen during daylight and use it up at night, so readings are often lowest just before dawn. This data set is simplified to show the effect of temperature alone.

Ormsby Brook Dissolved Oxygen: A Grade 7 Fish Habitat Worksheet — Grade 7 Science

Name: ____________________________ Date: ______________

Student Worksheet

Use this data from Ormsby Brook, a fictional cold-water stream. A team measured the water at four times on one summer day.

Time	Water temperature	Dissolved oxygen
6 a.m.	11 degrees C	9.2 mg/L
10 a.m.	15 degrees C	8.0 mg/L
2 p.m.	21 degrees C	6.4 mg/L
6 p.m.	24 degrees C	4.8 mg/L

At which time was the dissolved oxygen highest? Give the time and the reading.
At which time was the dissolved oxygen lowest? Give the time and the reading.
Most fish here need dissolved oxygen above 5 mg/L. At which reading did the brook fall below that level?
How much did the dissolved oxygen drop from 6 a.m. to 6 p.m.? Show your subtraction.
The water temperature rose from 11 degrees C to 24 degrees C. By how many degrees did it rise?
Describe the pattern between water temperature and dissolved oxygen in this data.
Find the percent decrease in dissolved oxygen from the 6 a.m. reading to the 6 p.m. reading. Round to the nearest whole percent.
A student says the warm evening is the most dangerous time for fish in this brook. Use the data to explain whether you agree.

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: 6 a.m., 9.2 mg/L.
The 6 a.m. reading of 9.2 mg/L is the highest value in the table, and the water was coldest then at 11 degrees C.
Answer: 6 p.m., 4.8 mg/L.
The 6 p.m. reading of 4.8 mg/L is the lowest value in the table, and the water was warmest then at 24 degrees C.
Answer: 6 p.m. (4.8 mg/L).
Only the 6 p.m. reading of 4.8 mg/L is below the 5 mg/L level that most fish here need.
Answer: 4.4 mg/L.
9.2 mg/L minus 4.8 mg/L equals 4.4 mg/L.
Answer: 13 degrees C.
24 degrees C minus 11 degrees C equals a rise of 13 degrees C.
Answer: As the water gets warmer, the dissolved oxygen goes down.
The two are inversely related: each time the temperature rose in the table, the oxygen fell. Warm water holds less dissolved oxygen than cold water.
Answer: 48 percent.
The drop is 9.2 minus 4.8, which is 4.4 mg/L. Then 4.4 divided by 9.2 equals about 0.478, which rounds to a 48 percent decrease.
Answer: Agree.
Accept answers that use the data: the evening reading (6 p.m.) was warmest and had the least oxygen (4.8 mg/L), which is below the 5 mg/L fish need, so the warm evening is the most dangerous time.

Differentiation

Support

Give students the subtraction set up for items 4 and 5 (for example, a blank showing "9.2 − 4.8 = ___") and allow a calculator for the percent step in item 7. Highlight the oxygen column so students can compare readings quickly.

Extension

Ask students to predict the dissolved oxygen for a fifth reading taken when the water has cooled to 9 degrees C, if temperature were the only factor, and to explain their prediction using the pattern they described in item 6.

ELL supports

Pre-teach "dissolved oxygen," "temperature," and "rise" with a simple picture of a fish in water and arrows for up and down. Allow students to answer items 1, 2, and 3 by pointing to the correct row in the table before writing.