Cellular Energetics - AP Bio Unit 3 Practice & Q&A

Sep 29, 2026

AP Biology Unit 3 review focused on cellular energetics, including Gibbs free energy, enthalpy and entropy relationships, and how enzymes regulate activation energy without being consumed. Covers enzyme types and inhibition, denaturation factors, and both cellular respiration and photosynthesis pathways. Includes structured practice prompts for ATP synthesis contributions, pathway locations and inputs/outputs for glycolysis, Krebs cycle, electron transport, chemiosmosis, and light/calvin cycle. Provides a multiple-choice question on tracing labeled oxygen during photosynthesis.

LanguageEnglish

CategoryExam

FormatPDF

Pages22

Reading Time55 min

AccessFree to download

Today’s Plan

Enzymes

Cellular Respiration

Photosynthesis

Practice Questions Unit 3 Q&A

Cellular Energetics @apbiopenguins AP Biology students are penguins because they are Dressed for Success! You are now an AP Bio Penguin! Resource Reminders: Daily Review on IG stories 374 page Review Guide on Weebly Recorded FRQ Fridays on YouTube 120+ Quizizz Games on Weebly Review PowerPoints on Weebly Weebly: [www.apbiopenguins.weebly.com](www.apbiopenguins.weebly.com) Today’s Plan Enzymes Cellular Respiration Photosynthesis Practice Questions Unit 3 Q&A Endergonic Reaction • Not spontaneous • ABSORB energy • Example: ADP + Pi → ATP • Spontaneous • RELEASE energy • Example: ATP → ADP + Pi Exergonic Reaction Gibbs Free Energy & Reactions Change in Gibbs Free Energy Temperature (K) ~~ ~~ ∆􀜩 = ∆􀜪 − 􀜶∆􀜵 Change in Enthalpy What is Gibbs Free Energy? • Energy available to do work Change in Entropy ∆􀜩 = ∆􀜩􀯙 − ∆􀜩 􀯜 Enzymes Functions • Biological catalyst • Speeds up chemical reactions • Reduces the activation energy Important Notes: • Enzymes are PROTEINS • Are NOT consumed by the reaction • Have no effect on the change in Gibbs Free Energy Competitive: • Binds to active site Noncompetitive: • Binds to allosteric site Denaturation Environmental Temperatures pH (outside of optimal range) Salinity Inhibitors Cellular Respiration Glycolysis • Location: Cytosol • Starting Material: Glucose • Products: 2 Pyruvate 2 NADH 2 ATP Oxidative Phosphorylation • Location: Mitochondrial Cristae • Starting Material: NADH/FADH2 (electrons) • Product: ATPs • Two Parts: Electron Transport Chain & Chemiosmosis Electron Transport Chain • Protons pumped into IM space • Generates proton gradient • Final electron acceptor: OXYGEN Krebs Cycle • Location: Mitochondrial Matrix • Staring Material: Acetyl CoA • Products: 2 CO2 3 NADH 1 FADH2 1 ATP Chemiosmosis • ATP Synthase uses proton gradient • Synthesizes ATP Cellular respiration includes the metabolic pathways of glycolysis, the Krebs cycle, and the electron transport chain, as represented in the figures. In cellular respiration, carbohydrates and other metabolites are oxidized, and the resulting energy-transfer reactions support the synthesis of ATP. (a) Using the information above, describe ONE contribution of each of the following in ATP synthesis. Catabolism of glucose in glycolysis and pyruvate oxidation Oxidation of intermediates in the Krebs cycle Formation of a proton gradient by the electron transport chain Photosynthesis Light Reactions Calvin Cycle • Location: Thylakoid Membrane • Starting Material: Water (electrons) Photons (energy) • Products: ATP NADPH Linear Electron Flow • PS I & PS II • Synthesizes ATP & NADPH Cyclic Electron Flow • PS I ONLY • Synthesizes ATP ONLY Electron Transport Chain • Protons are pumped into the thylakoid space • Location: Stroma • Starting Material: 3 CO2 9 ATP 6 NADPH • Products: G3P Multiple Choice Practice: The chemical reaction for photosynthesis is 6 CO2 + 12 H2O + light energy → C6H12O6 + 6 O2 + 6 H2O If the input water is labeled with a radioactive isotope of oxygen, 18O, then the oxygen gas released asthe reaction proceeds is also labeled with 18O. Which of the following is the most likely explanation? a. During the light reactions of photosynthesis, water is split, the hydrogen atoms combine with the CO2 , and oxygen gas is released. b. During the light reactions of photosynthesis, water is split, removing electrons and protons, and oxygen gas is released. c. During the Calvin cycle, water is split, regenerating NADPH from NADP + and oxygen gas is released d. During the Calvin cycle, water is split, the hydrogen atoms are added to intermediates of sugar synthesis, and oxygen gas is released.

FAQs

How do endergonic and exergonic reactions relate to energy changes?

Endergonic reactions are not spontaneous and absorb energy, while exergonic reactions are spontaneous and release energy. The document links these ideas to the ADP + Pi ↔ ATP examples.

What role do enzymes play in chemical reactions?

Enzymes are proteins that act as biological catalysts. They speed up reactions by reducing activation energy, are not consumed by the reaction, and do not affect the change in Gibbs free energy.

How does ATP synthesis occur during cellular respiration?

ATP synthesis is supported by glycolysis producing ATP and NADH, the Krebs cycle producing additional electron carriers, and the electron transport chain creating a proton gradient. Chemiosmosis then uses the proton gradient to drive ATP synthase to synthesize ATP.

Sep 29, 2026

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