AP Biology Unit 8: Ecology

Unit 8 covers ecology: population dynamics, community interactions, energy flow and disruptions to ecosystems. Most questions supply data and ask what it implies rather than testing definitions.

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154 questions9 CED topics91% with a figure
How this unit behaves

What 154 questions on it look like

It spans 9 CED topics, which is wide enough that "I've studied this unit" is not a meaningful statement. Track your accuracy by topic, not by unit.

91% of the questions come with a figure — a graph, diagram or data display. Reading the figure correctly is most of the work before any content knowledge applies.

Population Ecology42
Community Ecology37
Energy Flow Through Ecosystems20
Biodiversity20
Disruptions to Ecosystems19
Responses to the Environment6
Energy Flow and Nutrient Cycling4
Effect of Density of Populations3

Questions per CED topic, top 8 of 9.

From the bank

Three real ecology questions

Drawn from the practice pool, not from the mock papers.

Population Ecology · Concept Explanation

What does carrying capacity describe?

  1. AThe number of chromosomes carried by each gamete
  2. BThe number of codons translated in one ribosome
  3. CCarrying capacity is an ecological population limitcorrect
  4. DThe amount of ATP made by one chloroplast per second
Why C is correct

Carrying capacity is the population size that an environment can sustain given limiting resources and conditions.

The stem asks students to explain a specific mechanism, not just recall a unit term: "What does carrying capacity describe". The correct choice is supported by Carrying capacity is the population size that an environment can sustain given limiting resources and conditions. The tempting alternatives such as number of chromosomes carried by each gamete or number of codons translated in one ribosome fail because they do not produce the same outcome described in the stem.

Common mistakes. Do not stop at a nearby term such as number of chromosomes carried by each gamete or number of codons translated in one ribosome. The explanation has to make "maximum population size an environment can sustain over time" fit this stem clue: "What does carrying capacity describe".

Energy Flow Through Ecosystems · Concept Explanation

Why is less energy typically available at higher trophic levels in an ecosystem?

  1. AConsumers create energy from nothing before feeding.
  2. BEnergy is used and lost as heat at each trophic transfercorrect
  3. COrganisms at higher levels always have smaller genomes.
  4. DEnergy is recycled perfectly from predators to producers.
Why B is correct

Energy transfer between trophic levels is inefficient because organisms use energy for metabolism and release heat. Therefore less energy is available to the next trophic level.

The stem asks students to explain a specific mechanism, not just recall a unit term: "Why is less energy typically available at higher trophic levels in an ecosystem". The correct choice is supported by Energy transfer between trophic levels is inefficient because organisms use energy for metabolism and release heat. The tempting alternatives such as Consumers create energy from nothing before feeding or Organisms at higher levels always have smaller genomes fail because they do not produce the same outcome described in the stem.

Common mistakes. Do not stop at a nearby term such as Consumers create energy from nothing before feeding or Organisms at higher levels always have smaller genomes. The explanation has to make "Energy is lost as heat and used for metabolism at each transfer" fit this stem clue: "Why is less energy typically available at higher trophic levels in an ecosystem".

Effect of Density of Populations · Concept Explanation

Which factor is most likely to become more limiting as population density increases in a small habitat?

  1. AA mutation that occurs in one individual before birth
  2. BTransmission of a contagious disease among crowded individualscorrect
  3. CA regional change in day length caused by Earth's orbit
  4. DA volcanic eruption that destroys the habitat at random
Why B is correct

Disease transmission often increases when individuals are crowded, making it a density-dependent limiting factor.

The stem asks students to explain a specific mechanism, not just recall a unit term: "Which factor is most likely to become more limiting as population density increases in a small habitat". The correct choice is supported by Disease transmission often increases when individuals are crowded, making it a density-dependent limiting factor. The tempting alternatives such as mutation that occurs in one individual before birth or regional change in day length caused by Earth's orbit fail because they do not produce the same outcome described in the stem.

Common mistakes. Watch for choices that mention mutation that occurs in one individual before birth or regional change in day length caused by Earth's orbit but do not match the evidence. The deciding evidence is: Disease transmission often increases when individuals are crowded, making it a density-dependent limiting factor

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FAQ

Ecology questions

What ecology maths appears?

Population growth rates, carrying capacity, and the roughly 10% energy transfer between trophic levels.

How are ecosystem disruptions tested?

By asking for the downstream effect — remove or add a species, then trace what happens to the rest of the community.
Last reviewed 2026-08-28. Unit and topic names follow the College Board course framework. Question counts describe the PrepScore practice bank, not the exam.
Topic by topic

Worked questions by topic

4 of this unit’s topics have enough practice questions for a page of their own.

Energy Flow Through Ecosystems24 questionsPopulation Ecology39 questionsCommunity Ecology33 questionsBiodiversity21 questions
Same course
Unit 1: Chemistry of Life160 questionsUnit 2: Cells162 questionsUnit 3: Cellular Energetics240 questionsUnit 4: Cell Communication and Cell Cycle162 questionsUnit 5: Heredity157 questionsUnit 6: Gene Expression and Regulation240 questionsUnit 7: Natural Selection244 questions

Practise ecology until the reasoning is automatic.

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