Energy in Ecosystems — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Why is a food web a better model than a food chain for an ecosystem?
A) It shows only one path of energy
B) It shows many connected feeding relationships
C) It shows only producers in the ecosystem
D) It shows only the top predator's diet
Food webs show how many food chains overlap, which is more realistic for Grade 5 ecosystems.
2. About how much energy passes from one level of an energy pyramid to the next?
A) About 10 percent
B) About 50 percent
C) About 90 percent
D) About 100 percent
The 10 percent rule explains why higher levels of the pyramid have fewer organisms.
3. What happens to most of the energy that is not passed up the energy pyramid?
A) It becomes new producers
B) It is lost as heat
C) It is stored in soil
D) It is recycled by the sun
Most energy is released as heat during life activities like moving, breathing, and growing.
4. If all the hawks were removed from a food web, what would most likely happen?
A) Plants would disappear quickly
B) Mouse and snake populations could grow too large
C) The sun would stop providing energy
D) Decomposers would stop working
Removing a top predator can let prey populations grow and unbalance the ecosystem.
Part B: Fill in the Blank
Write the correct answer on each line.
1. A diagram showing how energy decreases at each level is an energy pyramid.
The energy pyramid shows that producers have the most energy and top predators have the least.
2. Many connected food chains make up a food web.
A food web shows the realistic many-to-many feeding links in an ecosystem.
3. About 10 percent of energy moves from one level to the next.
The 10 percent rule limits how many top predators an ecosystem can support.
4. Most energy lost between levels is released as heat.
Heat loss is why energy flows in only one direction through the ecosystem.
5. Removing one species from a food web can unbalance the whole ecosystem.
Every species has a role, so removing one can affect many other organisms.