Energy in Ecosystems — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Where does the energy in almost every ecosystem on Earth originally come from?
A) The soil
B) The sun
C) The ocean
D) The wind
The sun provides energy that producers turn into food, starting every food chain.
2. Which organisms have the most available energy in an ecosystem?
A) Producers
B) Primary consumers
C) Secondary consumers
D) Top predators
Producers have the most energy because energy decreases at each higher level.
3. Which group is essential for returning nutrients from dead organisms to the soil?
A) Producers
B) Herbivores
C) Decomposers
D) Top predators
Decomposers break down dead matter so producers can reuse the nutrients.
4. Which statement best describes how energy and matter move in an ecosystem?
A) Both energy and matter cycle endlessly
B) Energy flows one way, but matter cycles
C) Matter flows one way, but energy cycles
D) Both energy and matter flow only one way
Energy is lost as heat and must be replaced by the sun, while matter is recycled by decomposers.
Part B: Fill in the Blank
Write the correct answer on each line.
1. The original source of energy for almost every ecosystem is the sun.
Sunlight powers photosynthesis, which fuels every level of the ecosystem.
2. Producers convert sunlight into chemical energy stored in food.
Photosynthesis changes light energy into chemical energy that consumers can use.
3. Energy flows in one direction, but matter cycles in an ecosystem.
Decomposers and natural cycles keep matter moving through ecosystems again and again.
4. Top predators have the least available energy in an ecosystem.
Because of the 10 percent rule, top predators receive only a small fraction of total energy.
5. A balanced ecosystem needs producers, consumers, and decomposers.
All three groups must work together so energy and matter keep moving through the ecosystem.