Here are the answers to the questions on the worksheet, based on the 10% Rule shown in the diagram.
Q1) What is the 10% rule?
The 10% rule states that when energy is passed in an ecosystem from one trophic level to the next, only about 10% of the energy will be passed on. The rest is used by the organism for life processes (like movement and breathing) or lost as heat.
Q2) What is the significance of the 10% rule?
The significance is that it limits how much energy is available at higher levels of the food chain. Because so much energy is lost at each step, there is not enough energy to support many levels of predators. This is why food chains usually only have 4 or 5 levels and why there are always fewer top predators than producers.
Q3) Assume there are 1000 units of energy at the producer level. How many units of energy are available at each of the three consumer levels?
To solve this, we multiply the previous level's energy by 0.10 (or divide by 10).
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Producer Level: 1000 units
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Consumer-level 1: $1000 \times 0.10 = 100$ units
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Consumer-level 2: $100 \times 0.10 = 10$ units
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Consumer-level 3: $10 \times 0.10 = 1$ unit
Consumer-level 1: 100 units
Consumer-level 2: 10 units
Consumer-level 3: 1 unit
Q4) Suppose there are 500 units of energy available at the base of the pyramid. Approximately how much energy is available to the first-level consumer?
The "base" refers to the producers. To find the energy for the first-level consumer, we take 10% of the base amount.
Calculation: $500 \times 0.10 = 50$.
Final Answer:
Q1) The 10% rule states that only about 10% of the energy at one trophic level is transferred to the next level, while the remaining 90% is used for metabolic processes or lost as heat.
Q2) It explains why food chains rarely have more than four or five levels and why there are significantly fewer organisms at the top of the pyramid compared to the bottom.
Q3)
Consumer-level 1: 100 units
Consumer-level 2: 10 units
Consumer-level 3: 1 unit
Q4) 50 units
Parent Tip: Review the logic above to help your child master the concept of trophic level worksheet.
