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Analyze
Ecosystems

Trace how energy flows through living systems and discover how organisms depend on each other through symbiosis.

GED Science

What Is an Ecosystem?

An ecosystem is a community of living things (biotic factors) interacting with their physical environment (abiotic factors) such as sunlight, water, soil, and air.

Key Vocabulary

Producer
An organism (like a plant) that makes its own food using sunlight through photosynthesis.
Consumer
An organism that eats other organisms to get energy — herbivores, carnivores, omnivores.
Decomposer
Bacteria and fungi that break down dead matter, returning nutrients to the soil.

Where Energy Begins

Nearly all ecosystem energy starts with the Sun. Producers capture light energy and convert it into stored chemical energy (sugar) through photosynthesis:

The Food Chain

Sun Grass Producer Grasshopper 1° Consumer Frog 2° Consumer Hawk 3° Consumer

The 10% Rule of Energy

Producers — 10000 units 1000 units 100 units 10

Food Chain vs. Food Web

Food Chain
A single, straight pathway of energy: one producer eaten by one consumer, and so on.
Food Web
Many overlapping food chains. Shows the realistic, branching connections of an ecosystem.

Three Types of Symbiosis

+
Mutualism \( (+/+) \). Both species benefit. Example: bees get nectar, flowers get pollinated.
0
Commensalism \( (+/0) \). One benefits, the other is unaffected. Example: barnacles riding on a whale.
−
Parasitism \( (+/-) \). One benefits while harming the host. Example: a tick feeding on a dog.

Reading Symbiosis Notation

Scientists summarize each relationship with two signs, one for each organism. A plus means it benefits, a zero means no effect, and a minus means it is harmed.

How to Analyze an Ecosystem

1
Identify the energy source. Usually the Sun feeding the producers.
2
Trace the arrows. Follow energy from producers up through consumers.
3
Apply the 10% rule. Expect energy to drop sharply at each level.
4
Classify the interactions. Decide who benefits and who is harmed.

Example 1: Energy Math

A field of grass stores 50,000 units of energy. Using the 10% rule, how much energy reaches a tertiary consumer (the third consumer in the chain)?

Example 2: Classify the Relationship

A clownfish lives among a sea anemone's stinging tentacles. The clownfish gains protection, and it cleans the anemone and chases away predators. What type of symbiosis is this?

Example 3: Disrupting the Web

Algae Small Fish Snails Otter

Common Mistakes

✕ Reversed Arrows
Arrows point toward the eater, showing energy flow — not from the predator to prey.
✕ Energy Increases Up
Energy always decreases up a chain. Top predators have the least available energy.
✕ Confusing Symbiosis
Always check who is harmed. Parasitism harms the host; mutualism helps both.

Symbiosis Summary

Organism A Organism B
Mutualism+ Benefits+ Benefits
Commensalism+ Benefits0 No effect
Parasitism+ Benefits− Harmed
Predation+ Benefits− Killed

Question 1 of 5

In a food chain diagram, what does an arrow represent?

Question 2 of 5

Producers store 8,000 units of energy. By the 10% rule, about how much reaches a secondary consumer (two levels up)?

Question 3 of 5

A tick feeds on a dog's blood, harming the dog. This relationship is best described as:

Question 4 of 5

Why does an ecosystem usually support fewer top predators than producers?

Question 5 of 5

If a key prey species is removed, why is a food web usually more stable than a single food chain?