AP Biology Unit 3 Practice Test: Cellular Energetics
Master AP Biology Unit 3 with practice tests on photosynthesis, cellular respiration, ATP production, and fermentation. Includes data analysis and FRQ practice.
What Unit 3 Covers in AP Biology
Unit 3 is one of the most data-rich units on the AP Biology exam. Photosynthesis and cellular respiration are tested not only for content knowledge but also through graphical interpretation, experimental design, and cross-concept connections. Strong performance here requires both mechanistic understanding and science practice fluency.
Core Topics in Unit 3
Photosynthesis: Light Reactions and the Calvin Cycle
The light-dependent reactions occur in the thylakoid membranes — capturing solar energy, splitting water, producing ATP and NADPH, and releasing oxygen. The Calvin cycle (light-independent reactions) occurs in the stroma, using ATP and NADPH to fix CO₂ into G3P. AP questions often ask you to predict what happens to each stage if light availability or CO₂ concentration changes.
Cellular Respiration: Glycolysis, Krebs Cycle, and Oxidative Phosphorylation
Glycolysis (cytoplasm) converts glucose to pyruvate, yielding 2 ATP and 2 NADH per glucose. The Krebs cycle (mitochondrial matrix) completes oxidation, producing NADH, FADH₂, and CO₂. The electron transport chain and chemiosmosis (inner mitochondrial membrane) generate the majority of ATP. AP FRQs frequently present metabolic rate data and ask you to explain changes under varying conditions.
Fermentation
When oxygen is unavailable, fermentation regenerates NAD⁺ to sustain glycolysis. Lactic acid fermentation and alcoholic fermentation are both testable, including their ecological and experimental contexts.
ATP Production and Energy Accounting
Understand the relative ATP yields of each stage and the role of electron carriers (NAD⁺/NADH, FAD/FADH₂). AP Biology does not require strict ATP count memorisation, but conceptual understanding of where and how ATP is made is essential.
AP Science Practice Skills for Unit 3
- Data analysis: Interpreting O₂ production/consumption graphs, chromatography data, and respirometer results
- Experimental design: Designing photosynthesis or respiration rate experiments with proper controls
- Scientific argumentation: Connecting photosynthesis outputs to cellular respiration inputs in integrated explanations
How GradePerfect Tests Unit 3
Our Unit 3 practice test includes energy diagram interpretation, metabolic rate data analysis, and FRQ-style prompts that ask you to predict, explain, and connect energetics concepts across biological scales.