Energy Pyramids & Transfer Efficiency — Practice · Grade 7 Science

Chapter: Ecosystems, Matter & Energy

What this practice covers

By the end of Energy Pyramids & Transfer Efficiency you should be able to:

8 questions, written answer, multiple choice and numeric, each with a worked explanation.

Vocabulary used: trophic position, transfer efficiency, energy pyramid, biomass, energy budget.

Problem 1

Why can a few trees support many insects without contradicting energy flow?
Answer and explanation

Individual count differs from energy amount; organisms vary greatly in size and available energy.

Problem 2

If 200 of 1,000 units transfer, what percentage is modeled?
Answer and explanation

200/1,000×100=20%, rather than an assumed universal ten percent.

Problem 3

Does lower energy at the next position violate conservation?
Answer and explanation

No. Energy has other transfers and destinations; it is not all captured as next-level food.

Problem 4

Can a 10% energy transfer identify exact predator count?
Answer and explanation

No. Count depends on each organism’s needs and other ecological information not supplied by that fraction.

Problem 5

Illustrative energy model: producers provide 2,000 units; first consumers receive 300; second consumers receive 60 during the same interval. Calculate both transfer percentages and explain why the ten-percent shortcut and an energy-destruction claim are wrong.
Answer and explanation

The two modeled transfers are 15% and 20%. They are not both ten percent. Lower energy reaching the next position does not mean energy was destroyed; organisms use energy and transfer it into other pathways and heat. The model does not give the full separate budget or exact organism counts.

300/2,000×100=15%.

60/300×100=20%.

Identify other energy pathways and the stated boundary.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

A diagram gives 500 energy units and 100 animals. Can those labels be treated as the same measurement?
Answer and explanation

No. Energy amount and individual count are distinct quantities. A relationship between them requires further biological information.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

Which quantity belongs on an energy pyramid?
  1. Energy per stated boundary and interval
  2. Only individual names
  3. An uncalibrated image width
  4. A genetic allele letter
Answer and explanation

Energy per stated boundary and interval

Define energy units and comparable spatial and time boundaries.

Problem 8

A stipulated 10% transfer starts with 800 units. How many reach the next level?
Answer and explanation

80 energy units

0.10×800=80 under the stipulated rule.

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