Food Chains
A food chain shows how energy is transferred from one organism to another through feeding. Understanding food chains helps explain how organisms depend on one another and why changes to one population can affect an entire ecosystem.
What Is a Food Chain?
A food chain is a model that shows how energy is transferred from one organism to another through feeding relationships.
Each organism in a food chain represents a feeding step. The arrows show the direction that energy moves: from the organism being eaten toward the organism that eats it.
Most food chains begin with a producer, such as a plant or algae. Producers capture energy from sunlight and store that energy in organic molecules through photosynthesis. Consumers obtain energy by eating other organisms.
The arrow points toward the organism receiving the energy. In grass → rabbit, the rabbit receives energy from the grass, so the arrow points from grass to rabbit.
Trophic Levels
Each step in a food chain is called a trophic level. Trophic levels describe an organism's position in a feeding relationship and how it obtains energy.
Producers
Make their own food and capture energy.
Primary Consumers
Usually herbivores that eat producers.
Secondary Consumers
Eat primary consumers.
Tertiary Consumers
Eat secondary consumers.
Top Predators
Often have few or no natural predators.
How Energy Moves Through a Food Chain
The original energy entering most ecosystems comes from the Sun. Producers capture some of this light energy through photosynthesis and store it as chemical energy in organic molecules.
When a consumer eats a producer, some of that stored chemical energy is transferred to the consumer. When that consumer is eaten, some energy is transferred again.
The 10% Rule
On average, only about 10% of the energy stored at one trophic level becomes available to the next trophic level.
The other roughly 90% is not simply destroyed. Much of it is used by the organism for cellular respiration, movement, growth, reproduction, maintaining body functions, and other processes. Energy ultimately leaves the ecosystem as heat.
energy units
producers
energy units
primary consumers
energy units
secondary consumers
energy units
tertiary consumers
This is why food chains generally do not contain many trophic levels. There is progressively less usable energy available at each higher level.
Examples of Food Chains
Food chains occur in virtually every ecosystem. The exact organisms differ, but the basic pattern remains the same: energy moves from producers through a series of consumers.
Terrestrial Food Chain
Aquatic Food Chain
Ocean Food Chain
Food Chains vs. Food Webs
A food chain shows one pathway through an ecosystem. Real ecosystems are much more complicated. Most organisms eat more than one type of food and may also be eaten by several different organisms.
A food web combines multiple food chains to show these interconnected feeding relationships.
Food Chain
A simplified, linear pathway showing how energy moves through a particular sequence of organisms.
Grass → Rabbit → Fox
Food Web
Multiple interconnected food chains showing several feeding relationships within an ecosystem.
Because organisms are interconnected, a change in one population can affect other populations throughout a food web.
Energy Pyramids
An energy pyramid represents the amount of available energy at each trophic level. Producers form the broad base because they contain the greatest amount of energy available to the rest of the food chain.
As you move upward, the amount of available energy decreases. This pattern helps explain why populations at higher trophic levels are often smaller and why food chains tend to be relatively short.
Where Do Decomposers Fit?
Decomposers, such as fungi and many bacteria, break down dead organisms and organic waste. They obtain energy from this material and return nutrients to the environment.
Decomposers are not simply another step at the end of every food chain. Instead, they interact with material from all trophic levels.
Think of decomposers as connecting the whole ecosystem.
Dead plants, dead animals, and waste products can all become resources for decomposers.
This is an important distinction: energy flows through ecosystems, while matter and nutrients are continually recycled.
What Happens When a Food Chain Changes?
Because organisms are connected through feeding relationships, changes to one population can have effects at other trophic levels.
Removing a Predator
If a predator population decreases, populations of its prey may increase, potentially affecting the organisms those prey consume.
Losing Producers
A decline in producers reduces the amount of energy entering the food web and can affect consumers at multiple trophic levels.
Pollution
Pollutants can enter ecosystems and move through feeding relationships, potentially affecting organisms at different trophic levels.
Common Misconceptions
If You See This on a Test, Think This
Quick Practice
1. In the chain grass → rabbit → fox, which organism is the producer?
2. In grass → rabbit → fox, which organism receives energy directly from the rabbit?
3. If producers contain 10,000 units of energy, approximately how much energy would be available to the primary consumers?
4. What is the difference between a food chain and a food web?
5. Why are producers important to almost every food chain?
6. What happens to much of the energy that is not transferred to the next trophic level?
Key Takeaways
- A food chain shows the transfer of energy through feeding relationships.
- Food chains generally begin with producers.
- Each step in a food chain is a trophic level.
- The arrow points toward the organism receiving energy.
- Only a fraction of energy is transferred to the next trophic level.
- The 10% rule helps explain why less energy is available at higher trophic levels.
- Food webs show the many interconnected feeding relationships that exist in real ecosystems.
- Decomposers break down dead material and help return nutrients to the environment.
- Energy flows through ecosystems, while matter and nutrients are recycled.
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