AP Environmental Science Flashcards: Energy Flow and the 10% Rule
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
How do the laws of thermodynamics relate to the flow of energy in ecosystems?
The laws of thermodynamics explain the mechanism behind the energy decrease at each trophic level, as energy is lost (often as heat) during metabolic processes.
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How do the laws of thermodynamics relate to the flow of energy in ecosystems?
The laws of thermodynamics explain the mechanism behind the energy decrease at each trophic level, as energy is lost (often as heat) during metabolic processes.
A secondary consumer eats a primary consumer. If the primary consumer obtained 200 kcal from producers, how much energy does the secondary consumer gain?
Applying the 10% rule, the secondary consumer would gain approximately 10% of the energy, which is about 20 kcal.
Define the rule that governs the efficiency of energy transfer in a food chain.
The 10% rule approximates the efficiency, stating that only about 10% of the energy from one trophic level is incorporated into the next.
If producers in a food web start with 1,000,000 kcal of energy, how much energy is available for a tertiary consumer?
Following the 10% rule across three transfers, the tertiary consumer would have access to approximately 1,000 kcal of the original energy (1,000,000 -> 100,000 -> 10,000 -> 1,000).
Why can't 100% of energy be transferred between trophic levels?
Due to the laws of thermodynamics, energy is lost at each transfer, primarily as metabolic heat, making a 100% efficient transfer impossible.
What is the general trend of energy as it flows through an ecosystem?
Energy consistently decreases as it flows from lower to higher trophic levels within an ecosystem.
What is the term for the principle describing the reduction of available energy at successively higher levels in a food chain?
This principle is known as the 10% rule, which approximates the rate of energy loss as it flows through an ecosystem.
What scientific principles explain the energy loss between trophic levels?
The loss of energy that occurs when energy moves from lower to higher trophic levels can be explained through the laws of thermodynamics.
If a producer level contains 5,000 kcal of energy, approximately how much energy is available to the primary consumers?
Based on the 10% rule, only about 10% of the energy, or approximately 500 kcal, would be passed on to the primary consumers.
What is the 10% rule?
The 10% rule approximates that in the transfer of energy from one trophic level to the next, only about 10% of the energy is passed on.