An ecosystem is a community of living things interacting with each other and their environment. A food chain shows a simple line of energy transfer (grass → rabbit → fox), while a food web shows the more realistic, interconnected network of feeding relationships in an ecosystem. Energy flows in one direction, starting from the sun through producers (plants), to consumers, and only about 10% of energy passes to the next level — the rest is lost as heat.
Example
In a food chain grass → rabbit → fox, the grass captures energy from the sun through photosynthesis; the rabbit eats the grass, gaining some of that energy; the fox eats the rabbit, gaining only a fraction of the energy the rabbit had — most is lost along the way as heat from each animal's life processes.
Key terms
Producer:
An organism (usually a plant) that makes its own food from sunlight.
Consumer:
An organism that eats other organisms for energy.
Food web:
The interconnected network of feeding relationships in an ecosystem.
Questions
1. A producer is an organism that:
Makes its own food from sunlight
Only eats other animals
Never uses energy
Is always an animal
2. A consumer is an organism that:
Eats other organisms for energy
Makes its own food from sunlight
Is always a plant
Uses no energy at all
3. A food chain shows:
A simple line of energy transfer between organisms
A random collection of unrelated facts
Only plants, never animals
The weather in an ecosystem
4. A food web shows:
The interconnected network of feeding relationships
A single food chain only
Only producers
A type of map with no biology
5. Energy in an ecosystem originally comes from:
The sun
The soil only
Animals themselves
Nowhere, it appears randomly
6. An ecosystem is:
A community of living things interacting with their environment
A single animal only
A type of rock formation
A man-made structure only
7. In the food chain grass → rabbit → fox, which is the producer?
Grass
Rabbit
Fox
None of them
8. In the food chain grass → rabbit → fox, the fox is a:
Consumer
Producer
Neither
A type of plant
9. Roughly what percentage of energy passes from one level of a food chain to the next?
About 10%
About 50%
About 90%
100%
10. Most energy lost between levels of a food chain is lost as:
Heat, from life processes like movement and growth
New matter created from nothing
Sound only
Light only
11. Why is a food web generally a more accurate model of an ecosystem than a single food chain?
Most organisms eat and are eaten by multiple different species, not just one
Food webs never include producers
Food chains are always more detailed
Real ecosystems only ever have one feeding relationship
12. If a disease wiped out all the rabbits in an ecosystem, the food web suggests foxes would likely:
Need to rely more on other food sources, if available
Be completely unaffected
Immediately become producers
Have no possible response
13. Decomposers (like fungi and bacteria) play a role in ecosystems by:
Breaking down dead organisms and recycling nutrients
Producing all the ecosystem's energy from sunlight
Only eating living plants
Having no role at all
14. A top predator with no natural enemies is called a(n):
Apex predator
Producer
Decomposer only
Non-living part of the ecosystem
15. Why does energy only flow in one direction through an ecosystem (sun → producers → consumers), rather than cycling back?
Energy is lost as heat at each stage and cannot be recaptured by earlier organisms
Energy flows in every direction equally
Only consumers ever have energy
This one-directional flow is incorrect
16. Removing a keystone species (one with a disproportionately large ecosystem impact) can cause:
Significant disruption throughout the food web
No noticeable change at all
Only producers to be affected
The ecosystem to instantly improve
17. Why do apex predators typically exist in much smaller numbers than producers in a stable ecosystem?
Energy loss at each trophic level limits how much energy is available higher up the chain
Apex predators need no energy to survive
Producers require more energy than predators
Population size has no relationship to energy flow
18. Introducing a new predator species with no natural competitors into an ecosystem can:
Disrupt the existing food web and reduce native species' populations
Always have zero effect on the ecosystem
Automatically improve biodiversity with no downsides
Only affect producers, never consumers
19. Why is biodiversity (a wide variety of species) generally considered important for ecosystem stability?
More diverse food webs are more resilient to the loss of any single species
Biodiversity always makes ecosystems less stable
A single species is always sufficient for stability
Diversity has no connection to ecosystem health
20. Overfishing a key prey fish species in an ocean ecosystem would most likely lead to:
Declining populations of the predators that depend on it
No effect on any other species
An increase in producers with no other changes
Immediate recovery with no consequences
21. Why do scientists study interdependence between species rather than just studying species in isolation?
Changes to one species can ripple through the whole ecosystem via feeding relationships
Species never affect one another
Isolated study always gives the full picture
Interdependence is only relevant to plants
Answer key (parent copy)
1. Makes its own food from sunlight
2. Eats other organisms for energy
3. A simple line of energy transfer between organisms
4. The interconnected network of feeding relationships
5. The sun
6. A community of living things interacting with their environment
7. Grass
8. Consumer
9. About 10%
10. Heat, from life processes like movement and growth
11. Most organisms eat and are eaten by multiple different species, not just one
12. Need to rely more on other food sources, if available
13. Breaking down dead organisms and recycling nutrients
14. Apex predator
15. Energy is lost as heat at each stage and cannot be recaptured by earlier organisms
16. Significant disruption throughout the food web
17. Energy loss at each trophic level limits how much energy is available higher up the chain
18. Disrupt the existing food web and reduce native species' populations
19. More diverse food webs are more resilient to the loss of any single species
20. Declining populations of the predators that depend on it
21. Changes to one species can ripple through the whole ecosystem via feeding relationships