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AP Environmental Science Practice Quiz: Energy Flow and the 10% Rule

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 9 questions to check your progress.

Question 1 of 9

According to the 10% rule, what happens to the energy as it is transferred from one trophic level to the next?

All Questions (9)

According to the 10% rule, what happens to the energy as it is transferred from one trophic level to the next?

A) Only about 10% of the energy is passed on.

B) 90% of the energy is passed on.

C) Energy is created at each new trophic level.

D) The amount of energy remains constant.

Correct Answer: A

The provided content explicitly states that the 10% rule approximates that only about 10% of the energy from one trophic level is passed on to the next.

If the producer level in an ecosystem has 20,000 kcal of energy, approximately how much energy is available for the primary consumers?

A) 200 kcal

B) 2,000 kcal

C) 18,000 kcal

D) 20,000 kcal

Correct Answer: B

Based on the 10% rule, primary consumers will receive about 10% of the energy from the producers. 10% of 20,000 kcal is 2,000 kcal.

Which scientific principle provides the fundamental explanation for the loss of energy as it flows through ecosystems?

A) The theory of evolution

B) The principle of competitive exclusion

C) The laws of thermodynamics

D) The process of nutrient cycling

Correct Answer: C

The content states that 'The loss of energy that occurs when energy moves from lower to higher trophic levels can be explained through the laws of thermodynamics.'

Which statement best describes the overall pattern of energy flow in an ecosystem?

A) Energy is continuously recycled from top predators back to producers.

B) The total energy in an ecosystem increases with each trophic level.

C) Energy decreases as it moves from lower to higher trophic levels.

D) Energy is transferred between trophic levels without any loss.

Correct Answer: C

The first point of the provided content states that energy decreases as it flows through ecosystems, meaning less energy is available at each subsequent trophic level.

If a tertiary consumer has 15 kcal of energy, how much energy was required at the producer level to support it, according to the 10% rule?

A) 150 kcal

B) 1,500 kcal

C) 15,000 kcal

D) 150,000 kcal

Correct Answer: C

To find the producer energy, we must work backward. The secondary consumer level needed 15 kcal / 0.10 = 150 kcal. The primary consumer level needed 150 kcal / 0.10 = 1,500 kcal. The producer level needed 1,500 kcal / 0.10 = 15,000 kcal.

The 10% rule is considered an approximation rather than a fixed natural law. This is because the underlying principles that govern energy transfer are the...

A) laws of thermodynamics, which account for complex and variable energy transformations.

B) specific dietary preferences of each organism in the food web.

C) exact number of organisms at each trophic level.

D) rate of photosynthesis, which is constant across all ecosystems.

Correct Answer: A

The rule is a simplification. The content links the energy loss to the laws of thermodynamics, which describe the complex and not perfectly efficient conversion of energy (e.g., into heat, metabolic processes), making a simple 10% figure an approximation.

In a food chain consisting of grass, grasshoppers, mice, and hawks, which trophic level would have the least amount of available energy?

A) Grass (Producers)

B) Grasshoppers (Primary Consumers)

C) Mice (Secondary Consumers)

D) Hawks (Tertiary Consumers)

Correct Answer: D

Based on the principle that energy decreases as it flows through ecosystems, the highest trophic level (the hawks) will have the least amount of energy available to it from the original source (the grass).

The fact that approximately 90% of energy is NOT passed on to the next trophic level is a direct consequence of...

A) energy being destroyed by consumers.

B) the laws of thermodynamics.

C) biomass decreasing at higher levels.

D) producers being inefficient at photosynthesis.

Correct Answer: B

The provided content directly links the loss of energy between trophic levels to the laws of thermodynamics. This energy is not destroyed but is converted to other forms, such as heat, or used for metabolic processes by the organism.

A student claims that since energy is lost at each trophic level, ecosystems are fundamentally inefficient. Which concept from the provided text supports this claim?

A) The 10% rule, which quantifies the significant energy loss between levels.

B) The flow of energy from producers to consumers.

C) The existence of multiple trophic levels in an ecosystem.

D) The role of decomposers in the ecosystem.

Correct Answer: A

The 10% rule demonstrates the inefficiency of energy transfer. The fact that only a small fraction of energy moves to the next level supports the idea that the overall process of energy flow is inefficient from a transfer perspective.