Food Webs and Energy — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A field has grass, mice, snakes, and hawks. Which food chain is in the correct order?
A) hawk → snake → mouse → grass
B) grass → mouse → snake → hawk
C) mouse → grass → hawk → snake
D) snake → hawk → grass → mouse
Energy flows from producer (grass) to primary consumer (mouse) to secondary consumer (snake) to tertiary consumer (hawk).
2. Why can an ecosystem support more rabbits than wolves?
A) Wolves are bigger animals
B) Less energy is available at higher trophic levels
C) Rabbits reproduce faster than wolves
D) Wolves live in smaller habitats
The 10% rule means far less energy reaches carnivores than herbivores. Less energy available = fewer animals supported.
3. Which is the best example of a decomposer?
A) eagle
B) mushroom
C) deer
D) sunflower
Mushrooms are fungi that break down dead organic material, making them decomposers.
4. What would most likely happen if a new predator that eats rabbits is introduced to a grassland ecosystem?
A) Grass populations would decrease
B) Rabbit populations would decrease
C) Snake populations would increase
D) Decomposer populations would double
Introducing a new rabbit predator increases predation pressure, reducing the rabbit population.
Part B: Fill in the Blank
Write the correct answer on each line.
1. An ecosystem with many different food chains woven together is more resistant to change.
More complex food webs are more stable because the loss of one species can be offset by alternative feeding pathways.
2. Scavengers like vultures eat animals that are already dead.
Scavengers consume dead animals (carrion). They play an important role in decomposition and nutrient recycling.
3. Without decomposers, dead organisms would pile up and nutrients would not return to the soil.
Decomposers are essential for nutrient cycling. Without them, nutrients would be locked in dead matter indefinitely.
4. Energy flows in one direction through a food chain, from producers to consumers.
Energy in food chains moves only forward (producer → consumer), not backward. This is why arrows point one way.
5. An invasive species can disrupt a food web by competing with native organisms for resources.
Invasive species compete for food, space, and other resources, often outcompeting native species and disrupting ecosystems.