Food Webs and Energy — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. A invasive species is one that is not native to an ecosystem and can disrupt food webs.
An invasive species comes from outside the ecosystem and often has no natural predators there. Without predators to keep it in check, it can take over and throw the food web out of balance.
2. When prey populations decrease, predator populations usually decrease too.
Predators depend on prey for food, so when prey numbers drop, predators have less to eat. With less food available, fewer predators can survive and their population decreases too.
3. An energy pyramid is widest at the bottom because producers hold the most energy.
Producers at the bottom of the pyramid capture the most energy from the sun. Each level above loses about 90% of its energy as heat, so the pyramid gets narrower toward the top.
4. Vultures are scavengers because they feed on animals that have already died.
Vultures are scavengers because they eat carrion, which is the remains of already-dead animals. Unlike predators, scavengers do not hunt or kill their own prey.
5. A food web with many species is more stable than one with only a few species.
When a food web has many species, animals can switch to other food sources if one disappears. Fewer species means fewer backup options, making the whole ecosystem more fragile.
6. Organisms at the same feeding level in an energy pyramid share a trophic level.
"Trophic" comes from a Greek word meaning "feeding." Each trophic level groups together all the organisms that are the same number of steps away from the producers.
7. If all the plants in a grassland died, the herbivores would be the first consumers to lose food.
Herbivores eat plants directly, so they would be the first to starve if all the plants died. Carnivores would be affected later, once the herbivore populations dropped.
8. Nutrients are recycled in an ecosystem, but energy flows in only one direction.
Unlike nutrients that cycle back through decomposition, energy travels in only one direction through a food web. It enters from the sun, passes through organisms, and is eventually lost as heat.
9. Tiny animals called zooplankton eat phytoplankton and are primary consumers in the ocean.
Zooplankton are tiny animals that drift in the ocean and feed on phytoplankton. Since phytoplankton are producers, zooplankton are primary consumers, the first animal link in the ocean food web.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each term to its correct definition.
food chain
→ a single path of energy from producer to consumer
a feeding step in a food chain or web
food web
→ many overlapping food chains in an ecosystem
many overlapping food chains in an ecosystem
energy pyramid
→ a diagram showing energy decreases at each level
a single path of energy from producer to consumer
trophic level
→ a feeding step in a food chain or web
a diagram showing energy decreases at each level
Correct matches: food chain → a single path of energy from producer to consumer; food web → many overlapping food chains in an ecosystem; energy pyramid → a diagram showing energy decreases at each level; trophic level → a feeding step in a food chain or web.