Grade 3
The Human Knowledge Project
Unit 9 — Ecosystems and Living Things
Welcome back!
No living thing exists completely alone.
Plants, animals, fungi, and tiny microorganisms all interact with one another and with their environment.
These relationships form ecosystems.
Today you will learn how living things depend upon one another to survive.
What Is an Ecosystem?
An ecosystem is a community of living things and the nonliving environment around them.
An ecosystem includes:
- plants
- animals
- fungi
- bacteria
- soil
- water
- air
- sunlight
All of these parts work together.
Producers
Plants are called producers.
They make their own food using:
- sunlight
- water
- carbon dioxide
This process is called photosynthesis.
Plants provide food for nearly every ecosystem on Earth.
Consumers
Animals cannot make their own food.
They are called consumers.
Different consumers eat different foods.
Some are:
- herbivores (eat plants)
- carnivores (eat animals)
- omnivores (eat both plants and animals)
Each has an important role in the ecosystem.
Decomposers
Some organisms break down dead plants and animals.
These are called decomposers.
Examples include:
- mushrooms
- many fungi
- bacteria
- earthworms
Decomposers return nutrients to the soil, helping new plants grow.
Without decomposers, dead material would continue to pile up.
Food Chains
Energy moves through an ecosystem.
A simple food chain might be:
Grass
↓
Rabbit
↓
Fox
↓
Decomposers
Each living thing depends on the one before it.
Food Webs
Most ecosystems contain many connected food chains.
Together they form a food web.
A food web shows that living things often have more than one food source and may be eaten by more than one predator.
Food webs better represent how nature actually works.
Habitats
A habitat is the natural home of a living thing.
Habitats provide:
- food
- water
- shelter
- space
Examples include:
- forests
- grasslands
- deserts
- wetlands
- rivers
- oceans
Different habitats support different communities of life.
Protecting Ecosystems
Healthy ecosystems benefit all living things.
People can help by:
- reducing pollution
- recycling
- conserving water
- protecting forests
- preserving wildlife habitats
- planting native plants
Small actions can make a meaningful difference.
Activity
Choose one ecosystem.
Examples:
- forest
- pond
- ocean
- desert
- prairie
Draw a simple food web showing at least:
- one producer
- two consumers
- one decomposer
Explain how the organisms depend on one another.
Practice
Answer these questions.
What is an ecosystem?
What is a producer?
What is a consumer?
Why are decomposers important?
What is the difference between a food chain and a food web?
Name three ways people can help protect ecosystems.
Review
Today you learned:
- ecosystems include living and nonliving parts
- producers make food using sunlight
- consumers depend on other organisms for food
- decomposers recycle nutrients
- food webs connect many food chains
- healthy ecosystems support all life
Every living thing plays a role in keeping nature balanced.
Looking Ahead
Next we will investigate forces and motion.
You will discover how pushes, pulls, gravity, friction, and simple machines help explain how objects move.