Food Webs and Energy — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. The base of an energy pyramid is made up of producers.
Producers (plants) form the broadest base of an energy pyramid because they have the most available energy.
2. A trophic level is a feeding level in a food chain.
Each trophic level represents a step in the food chain: producers (level 1), primary consumers (level 2), etc.
3. Only about ten percent of energy is passed from one trophic level to the next.
The 10% rule: approximately 90% of energy is lost as heat at each trophic level; only ~10% moves up.
4. Secondary consumers eat primary consumers.
Primary consumers eat producers; secondary consumers eat primary consumers — one level above.
5. An organism that eats a primary consumer is called a secondary consumer.
Secondary consumers occupy the third trophic level and eat herbivores (primary consumers).
6. Decomposers recycle nutrients back into the soil for producers to use.
Decomposers break down dead matter, releasing minerals and nutrients that plants need for growth.
7. A food web is more complex than a single food chain because it has many paths.
Food webs show the realistic complexity of ecosystems with overlapping feeding relationships.
8. Hawks, wolves, and sharks are examples of top predators.
Top predators (apex predators) have no natural predators themselves and sit at the peak of the food chain.
9. Plants use sunlight, water, and carbon dioxide to make food through photosynthesis.
Photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂. Plants convert light energy into chemical energy stored in glucose.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
producer
→ makes its own food from sunlight
breaks down dead organisms
primary consumer
→ eats producers directly
makes its own food from sunlight
secondary consumer
→ eats primary consumers
eats primary consumers
decomposer
→ breaks down dead organisms
eats producers directly
Producer → makes own food; primary consumer → eats producers; secondary consumer → eats primary consumers; decomposer → breaks down dead organisms.