Ecosystems — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. An energy pyramid shows that energy decreases at each level of a food chain.
An energy pyramid is widest at the bottom (most energy with producers) and narrows to the top.
2. Only about ten percent of energy passes from one level to the next in a food chain.
The 10% rule: only about 10% of energy at one level is available to the next. The rest is lost as heat.
3. Most energy at each level is lost as heat when organisms use it for daily activities.
Organisms use energy for metabolism, movement, and growth. Most of this energy is released as heat.
4. Producers form the bottom level of every energy pyramid because they hold the most energy.
Producers capture solar energy and have the most. Each consumer level has less and less.
5. During photosynthesis, plants take in carbon dioxide from the air and water from the soil.
Photosynthesis equation: CO₂ + H₂O + sunlight → glucose + O₂.
6. Photosynthesis produces glucose for food and releases oxygen into the air.
Oxygen (O₂) is a by-product of photosynthesis and is essential for consumers to breathe.
7. The top of an energy pyramid has the least amount of energy available.
Each level loses ~90% of energy, so top predators have the least energy and can support fewest individuals.
8. Herbivores are on the second level of an energy pyramid just above the producers.
Level 1=producers, Level 2=herbivores (primary consumers), Level 3=secondary consumers, etc.
9. Without energy from the Sun, producers could not make food and the entire pyramid would collapse.
Solar energy is the foundation of almost all food chains. Without it, photosynthesis stops.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Producers
→ Hold the most energy because they capture it directly from sunlight
Eat producers and hold about ten percent of the original energy
Primary consumers
→ Eat producers and hold about ten percent of the original energy
Return nutrients to the soil so producers can grow again
Secondary consumers
→ Hold less energy because they are two steps from the producers
Hold the most energy because they capture it directly from sunlight
Decomposers
→ Return nutrients to the soil so producers can grow again
Hold less energy because they are two steps from the producers
Producers=most energy from sunlight(idx2); Primary consumers=eat producers ~10% energy(idx0); Secondary consumers=two steps from producers(idx3); Decomposers=return nutrients(idx1)