Little Lab Coats

When One Population Changes

Life Science — Ecosystems & Food Webs | Unit 1, Lesson 5 of 6

📚 Grade: 5th Grade⏱️ Duration: 45–60 minutes🔬 Subject: Life Science — Ecosystems & Food Webs

🦌↔️🦊

A change in one population can ripple through the food web.

📋 NGSS Standard:
5-LS2-1 — Develop a model to describe the movement of matter among plants, animals, decomposers, and the environment.

🎯 Learning Objective

Students will predict how a change in one population can affect other parts of a food web.

💡 The Big Idea

In a connected ecosystem, one change can ripple outward and affect many organisms.

🔬 The Science

Science Snapshot

Food-web changes can ripple outward because many populations are connected.

What is happening?

Populations in a food web are linked, so a change in one population can affect others. If producers shrink, herbivores may struggle. If predators increase or decrease, prey populations may shift too.

Why it works that way

These effects are not always simple or immediate. A change can travel through several steps in the web, and the size of the effect depends on how many relationships connect to that population and what alternatives exist.

Look for this in the lesson

Students should use evidence-based “if...then...” reasoning. The goal is not to memorize one outcome, but to explain why a change in one population can create a chain reaction.

Ask while you read: If one population changes, which connected populations might respond next and why?

📦 Materials

🏠 Household Items to Gather

Food web from previous lesson
Scenario cards
Worksheet and pencil

📋 Printables

Student worksheet page from this lesson

🧪 Investigation

Step 1 — Choose a scenario (5 min)
Examples: fewer rabbits, more insects, loss of a plant species.

Step 2 — Trace the first effect (10 min)
Find the organisms directly connected to the changing population.

Step 3 — Trace the ripple effects (10 min)
Follow at least two more likely changes through the web.

Step 4 — Record the prediction (10 min)
Students explain the changes using arrows or notes.

Step 5 — Defend the reasoning (10 min)
Share why the prediction makes sense based on the web.

💬 Discussion Questions

Why can one population change affect many organisms?Because the organisms are connected in a web.

Which effect would happen first?Start with the organisms directly connected.

Why are these predictions and not guarantees?Models help us reason, but real ecosystems are complex.

🚀 Extensions

Extension: Invent your own scenario and see whether a partner agrees with your predicted ripple effects.

👩‍🏫 Parent/Teacher Notes

Teaching move: Encourage students to use cautious language like may, could, or likely when making predictions.

Student Worksheet

Name: ________________________ Date: ________________________

1️⃣ Scenario

2️⃣ What changes first?

3️⃣ What changes next?

🔑 PARENT ANSWER KEY — Detach before giving worksheet to students

Sample Reasoning

If a prey population drops, predators may have less food and some producers may increase because fewer herbivores are eating them.

✅ What Success Looks Like

Student starts with direct relationships.
Student predicts at least one ripple effect.
Student uses food web evidence, not random guesses.