Classroom activity Grade 8 Science

Bickerton Brook Macroinvertebrate Index: A Card Sort

A grade 8 science activity where groups sort stream insect cards by pollution tolerance and calculate a biotic index for three sites on a fictional brook.

Grade: Grade 8
Subject: Science
Material: Classroom activity
Time: 45 min
Prep: Low prep
Materials: Printed and cut organism cards, three sheets of 12 per group, Three labeled site envelopes per group, Printed student handout, Calculators, Chart paper for the class comparison

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: Students interpret the organism counts from three sites as data, showing how the oxygen available at each site changes which populations the stream supports.

All materials for MS-LS2-1 →

MS-ESS3-3 NGSS

Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.

How this material aligns: The biotic index is itself a monitoring method, and handout item 8 asks students to name an upstream change that would raise the lowest site's score, which is the impact-reducing half of this standard.

All materials for MS-ESS3-3 →

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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 classify stream macroinvertebrates by their tolerance for pollution.
Students will calculate a biotic index score for three stream sites and rank them.
Students will explain what a change in the community of stream animals reveals about water quality.

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: macroinvertebrate, pollution tolerance, biotic index, indicator species, outfall

Teacher overview

Biologists judge a stream by what lives in it, because the animals cannot leave when conditions turn bad. Stonefly and mayfly young need cold, well-oxygenated water and vanish first when pollution arrives, while worms and midge larvae survive almost anywhere. In this card-sort activity, groups of three receive the animals collected at three sites along the fictional Bickerton Brook, sort each site's cards by pollution tolerance, and calculate a biotic index score that ranks the sites. Every card a group places in the sensitive column stands for an animal that survives only where the water holds enough oxygen and carries little pollution, so the sort itself reproduces what a biologist reads from a field sample.

Activity Directions

Set up the decks (5 min). Print and cut three sheets of the 12 organism cards for each group of three, since several kinds appear at more than one site. Fill three envelopes per group. Site A holds stonefly nymph, mayfly nymph, caddisfly larva, water penny, dragonfly nymph, damselfly nymph, crayfish, and aquatic worm. Site B holds mayfly nymph, dragonfly nymph, damselfly nymph, scud, aquatic worm, midge larva, leech, and pouch snail. Site C holds crayfish, scud, aquatic worm, midge larva, leech, and pouch snail.

Introduce tolerance groups (8 min). Show the three tolerance columns and explain the point values: sensitive kinds are worth 3, somewhat sensitive kinds are worth 2, and tolerant kinds are worth 1. Name one animal in each column and explain why it belongs there, connecting sensitivity to how much dissolved oxygen the animal needs.

Sort Site A (7 min). Groups open the Site A envelope, lay every card in the correct tolerance column, and count how many kinds landed in each column. They write those three counts on scratch paper, then compare them with the Site A row of the handout table and re-sort if the numbers disagree.

Sort Sites B and C (10 min). Groups repeat the sort for the other two envelopes, checking each result against the matching row of the handout table. Remind them to count kinds of animals, not individual cards of the same kind.

Calculate and post scores (10 min). Groups compute each site's index score with the relationship on the handout and write their three scores on the class chart paper. Compare the posted scores across groups and settle any that disagree by re-counting the columns together.

Debrief (5 min). End the activity once every group has posted three scores and answered the handout items. Ask two closing questions aloud: which site would students choose to swim in, and what did the missing stonefly and mayfly cards at Site C reveal that a single bottle of water could not?

Bickerton Brook Macroinvertebrate Index: A Card Sort — Grade 8 Science

Name: ____________________________ Date: ______________

Student Handout

The three sites lie along the fictional Bickerton Brook. Site A is in forest near the headwaters, Site B is downstream of a pasture, and Site C is downstream of a storm drain outfall in town.

Tolerance groups and point values:

Sensitive, 3 points each: stonefly nymph, mayfly nymph, caddisfly larva, water penny
Somewhat sensitive, 2 points each: dragonfly nymph, damselfly nymph, crayfish, scud
Tolerant, 1 point each: aquatic worm, midge larva, leech, pouch snail

Index score = (3 x sensitive kinds + 2 x somewhat sensitive kinds + 1 x tolerant kinds) divided by the total number of kinds found. Round each score to the nearest tenth.

A correct sort of the three envelopes gives the counts below. Check your own sort against this table before you calculate, and if a row does not match, find the card your group placed in the wrong column.

Site	Sensitive kinds	Somewhat sensitive kinds	Tolerant kinds	Total kinds
A	4	3	1	8
B	1	3	4	8
C	0	2	4	6

Rating scale: 2.6 to 3.0 is excellent, 2.1 to 2.5 is good, 1.6 to 2.0 is fair, and 1.0 to 1.5 is poor.

Site A has 4 sensitive kinds, 3 somewhat sensitive kinds, and 1 tolerant kind, for 8 kinds in all. Calculate Site A's index score.
Site B has 1 sensitive kind, 3 somewhat sensitive kinds, and 4 tolerant kinds, for 8 kinds in all. Calculate Site B's index score.
Site C has 0 sensitive kinds, 2 somewhat sensitive kinds, and 4 tolerant kinds, for 6 kinds in all. Calculate Site C's index score.
Use the rating scale to name the rating Site C earned.
How many more sensitive kinds did Site A have than Site C?
Site C had the most tolerant kinds and no sensitive kinds at all. What does that pattern suggest about conditions in the brook at Site C?
A water sample describes the moment it was collected. Explain why counting the kinds of animals living at a site tells you about conditions over many weeks instead.
Name one change the town could make upstream of Site C, and explain how that change would raise the site's index score over time.

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: 2.4.
(3 x 4) + (2 x 3) + (1 x 1) = 12 + 6 + 1 = 19, and 19 divided by 8 kinds = 2.375, which rounds to 2.4.
Answer: 1.6.
(3 x 1) + (2 x 3) + (1 x 4) = 3 + 6 + 4 = 13, and 13 divided by 8 kinds = 1.625, which rounds to 1.6.
Answer: 1.3.
(3 x 0) + (2 x 2) + (1 x 4) = 0 + 4 + 4 = 8, and 8 divided by 6 kinds = 1.333, which rounds to 1.3.
Answer: Poor.
A score of 1.3 falls in the 1.0 to 1.5 band of the rating scale, the lowest of the four ratings.
Answer: 4 more sensitive kinds.
Site A had 4 sensitive kinds and Site C had none, so the difference is 4.
Answer: Conditions at Site C are hard on sensitive animals.
Only animals that tolerate low oxygen and pollution remain, which points to runoff from the storm drain outfall lowering the oxygen or carrying pollutants that the sensitive kinds cannot survive.
Answer: The animals have been living there the whole time.
A macroinvertebrate that needs clean, cool water cannot survive even a short pollution event, so its absence records something that happened days or weeks earlier. A single water sample would miss that event entirely unless someone happened to collect during it.
Answer: Treat or slow the stormwater before it reaches the brook.
Accept any specific upstream change with a mechanism, such as adding a rain garden or swale that filters runoff before the outfall, keeping livestock fenced back from the pasture reach, or planting shade trees along the bank to keep the water cooler and hold more oxygen. Higher oxygen and less pollution would let sensitive kinds return, raising the number of 3-point kinds and the score with it.

Differentiation

Support

Give these groups pre-sorted decks with the tolerance column printed on the back of each card, so the sorting step confirms rather than tests the classification. Provide the index calculation for Site A already set up as (3 x 4) + (2 x 3) + (1 x 1), leaving only the division.

Extension

Have students design a fourth site for the fictional Bickerton Brook that would score in the excellent band, list which kinds must be present, prove the score with the calculation, and describe what the surrounding land would look like.

ELL supports

Use picture cards with both the common name and a simple drawing of each animal, and group them by column color as well as by label. Provide sentence frames such as "Site ___ scored ___ because it had ___ sensitive kinds." Allow students to answer items 6 through 8 orally to a partner before writing.

Extensions

Have students find whether a watershed group near them runs volunteer stream monitoring, then compare that group's scoring sheet with the simplified index used for the fictional Bickerton Brook and list two differences.