The Life Starter
Sign up
Grade 7 · lesson 2 of 4

Calculate a Model Transfer Efficiency

Find a supplied energy-transfer percentage without assuming a universal rate.

Download the grade pack

Supplied materials

  • Use the supplied fictional observations or model. Paper and pencil are optional; spoken answers are welcome. No equipment or real experiment is needed.

Learn the idea

A web gives relationships, while a quantitative model adds amounts for a stated interval. Transfer efficiency for this activity is consumer-growth energy divided by available food-growth energy, multiplied by 100%. It is not a percentage of all sunlight, and it does not count every destination of energy in the ecosystem.

In a fictional grasshopper route, 500 kJ of grass growth is available in the interval and 75 kJ becomes grasshopper growth. Of the 75 kJ, 15 kJ becomes frog growth. We assume these are complete amounts for this specified route and interval. The two transfer fractions differ, showing why a fixed ten-percent transfer should not be imposed on every step. Uncounted growth-route energy can be in uneaten matter, waste, or thermal transfers.

  1. Compute 75/500 × 100 for the first transfer.
  2. Compute 15/75 × 100 for the second.
  3. Calculate 15/500 × 100 for the whole two-step route.
  4. State the interval and growth-energy boundary of the percentages.
Worked example

See the method in action

Grass-to-grasshopper efficiency is 15%; grasshopper-to-frog is 20%. Frog growth is 3% of the initial grass-growth energy because 15/500 × 100 = 3%.

Your turn

Check your reasoning

Your answer is temporary and is not saved to an account. Download your current answer before leaving or reloading. Written work on paper or in another app stays in your own file.

If another supplied route has 200 kJ food growth and 30 kJ consumer growth, what is its transfer efficiency?

Feedback appears here after you check. This is practice, not a graded school assessment.

See the answer and explanation

15%

30/200 = 0.15, or 15%. This is the specified growth-to-growth fraction.

Take it further

Change consumer growth to 50 kJ while food growth remains 200. Efficiency becomes 50/200 × 100 = 25%.

Nothing here is saved to an account or sent to a teacher. The answer download includes your current choice and any checked feedback.

Check the subject sources

These LifeStarter passages, scenarios and exercises are authored for this Academy with AI assistance and review. External resources keep their publishers’ terms. A grade label suggests a starting level; it does not establish alignment with your school’s complete requirements.