AP Biology Unit 3: Cellular Energetics — Tips & Strategies

Cellular Respiration: Follow the Carbon

concept

Glycolysis splits glucose into 2 pyruvate (cytoplasm). Pyruvate oxidation and the Krebs cycle release CO2 (mitochondrial matrix). The ETC produces most ATP (inner membrane).

Chemiosmosis: The Proton Gradient Powers ATP

concept

Both photosynthesis and cellular respiration use an electron transport chain to pump H+ ions, creating a gradient. H+ flows back through ATP synthase, driving ATP production.

Fermentation Is NOT a Replacement for Aerobic Respiration

common-mistake

Fermentation only regenerates NAD+ so glycolysis can continue. It produces zero additional ATP. Total yield is just 2 ATP per glucose (from glycolysis alone).

Photosynthesis Rate Factors: Light, CO2, Temperature

exam-strategy

Photosynthesis rate is limited by whichever factor is least available (limiting factor principle). Graphs of rate vs. each variable plateau at saturation points.

Photosynthesis Overview: Two Stages, Two Locations

concept

Light reactions occur in thylakoid membranes (produce ATP and NADPH). The Calvin cycle occurs in the stroma (uses ATP and NADPH to fix carbon into G3P).

ETC Electron Carriers: Know the Order

memorization

In cellular respiration, electrons flow from NADH/FADH2 through complexes I-IV to oxygen (final electron acceptor). NADH enters at Complex I; FADH2 at Complex II.

Krebs Cycle Products Per Turn — Don't Over-Count

common-mistake

One turn of the Krebs cycle produces: 1 ATP (via GTP), 3 NADH, 1 FADH2, and 2 CO2. Since each glucose yields 2 acetyl-CoA, multiply everything by 2 for per-glucose totals.