College Board-Aligned Original Notes

AP Biology Unit 8 Topic 2: Energy flow through ecosystems

Connect Energy flow through ecosystems to a model, the evidence that supports it, and the variables that change the system.

Unit 8: Ecology. College Board exam weighting listed for this unit: 10%-15% of exam score.

What to Know

Identify the system, surroundings, and scale before explaining a process.
Use diagrams, graphs, and tables as evidence rather than decoration.
For quantitative questions, keep units visible from the setup through the final answer.
Always connect this topic back to the larger unit: Ecology.

Detailed Notes

Energy flow through ecosystems belongs to Ecology, so study it as part of a larger scientific system rather than as a stand-alone fact. Start by identifying what is being described, what is changing, and what evidence would let you defend a claim.

In AP Biology, strong answers usually connect a visible pattern to an underlying mechanism. That means explaining not only what happens, but why it happens at the particle, organism, environmental, or system level.

For AP-style questions, expect this topic to appear with graphs, diagrams, data tables, experiments, or written scenarios. Your job is to describe the evidence, apply the correct concept, and explain the reasoning that connects them.

Key Vocabulary

Ecosystem

A community of organisms and the physical environment with which they interact.

Population

A group of individuals of the same species living in the same area.

Community

All the interacting populations in an ecosystem.

Biodiversity

The variety of life at genetic, species, and ecosystem levels.

Carrying capacity

The maximum population size an environment can support over time.

Quick Practice

How would you explain Energy flow through ecosystems in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.