5th Grade Science Lesson

The Day the Kelp Forest Disappeared: Tracing Matter Through a Broken Web

Shared by A STEM Educator

5th GradeNGSS Phenomenon-BasedNGSS 5-LS2-150 min

Learning Objective

Students will be able to develop a model that describes the movement of matter among plants, animals, decomposers, and the environment, and use evidence from the kelp forest collapse to construct an explanation for how disrupting one part of the cycle affects the whole system (NGSS 5-LS2-1).

Lesson Overview

Students investigate how the decline of sea otters on the Pacific coast triggered a cascade of changes in the kelp forest ecosystem, using this phenomenon to trace how matter moves among producers, consumers, decomposers, and the environment. Students build and revise a system model to explain why matter cycling is essential to ecosystem health.

Materials

Anchor phenomenon image (projected)
Kelp Forest Food Web cards (1 set per group of 4)
String or yarn (various colors, ~2 meters per group)
Matter Movement Tracking Sheet (printed, 1 per student)
Sticky notes (3 colors: green, orange, brown)
Markers
Printed investigation data table
Pencils
Optional: short video clip of healthy vs. urchin barren kelp forest (2 min)

Scaffolded Task Progression

1Task 1

FOOD WEB MAPPING — Initial Observation

Your group has a set of organism cards for the kelp forest ecosystem. The organisms are: Kelp (giant seaweed), Sea Urchin, Sea Otter, Rockfish, Bald Eagle, Bacteria & Fungi, Sun, and Ocean Water/CO₂.

Step A: Sort the cards into three groups: PRODUCERS, CONSUMERS, and DECOMPOSERS. Record your groupings below.

Step B: Use yarn to connect organisms that have a feeding relationship. Draw arrows showing the direction matter/energy flows (from food → eater).

Step C: Where does the kelp get the matter to build its body? Draw a dotted line from 'Sun' and 'Ocean Water/CO₂' to the Kelp card.

[ Interactive graph / diagram — available in the full lesson ]

2Task 2

MATTER TRACKING — Where Does the Matter Go? Now that your web is built, use your three colors of sticky notes to track matter movement: • GREEN sticky note = matter moving INTO an organism (eating, absorbing) • ORANGE sticky note = matter leaving an organism as waste or breath (CO₂, poop) • BROWN sticky note = matter going to decomposers or back to environment For each organism below, place sticky notes on your web and answer:
A. When a sea urchin eats kelp, what happens to the matter in the kelp? Does ALL of it become sea urchin body? Where does the rest go?B. When a sea otter dies, what happens to the matter in its body?C. Draw a simple arrow cycle showing: Kelp → Sea Urchin → [what?] → back to environment → back to Kelp. Fill in the missing steps.

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