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Unit 3 · Cellular Energetics Flashcards Cheat Sheet Essentials Visual Review MC Practice FRQ Practice

AP Biology Unit 3 Visual Review

A topic-by-topic visual walkthrough of Cellular Energetics — enzymes and their environment, ATP and energy coupling, photosynthesis, and cellular respiration.

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TOPIC 3.1 Enzymes — Biological Catalysts without enzyme with enzyme free energy reaction progress → Enzymes LOWER activation energy (Eₐ) What an enzyme does Speeds up a reaction by lowering its activation energy — the energy barrier reactants must cross. It does NOT change whether a reaction is favorable, only how fast. Active site & specificity The substrate binds the enzyme's active site, forming an enzyme–substrate complex. "Induced fit" — the site molds around the substrate. Each enzyme is specific to its shape. Key facts Enzymes are (usually) proteins and are NOT consumed — one enzyme catalyzes reaction after reaction. Their names often end in "-ase" (e.g., lactase, DNA polymerase). Cofactors (metals) or coenzymes (vitamins) may be required helpers for the active site to work. Enzymes lower activation energy so reactions run fast enough for life — without being used up. The Review Hub · AP Biology Unit 3 TOPIC 3.2 Environmental Impacts on Enzyme Function optimum reaction rate temperature or pH → too low denatured Temperature & pH have an optimum Each enzyme works best at a specific temperature and pH. Beyond that, the protein DENATURES — its shape (and active site) unfolds, so it stops working. Concentration raises the rate — up to a point More substrate or more enzyme speeds the reaction until saturation — when every active site is full, adding more substrate no longer helps (the rate plateaus). Competitive inhibitor Binds the active site directly, blocking the substrate. Adding more substrate can outcompete it. Noncompetitive (allosteric) inhibitor Binds a different site (allosteric site) and changes the enzyme's shape, so the active site no longer fits. More substrate can't reverse it. Temperature, pH, and inhibitors all work by changing the enzyme's shape or its access to the substrate. The Review Hub · AP Biology Unit 3 TOPIC 3.3 Cellular Energy — ATP STRUCTURE OF ATP adenine ribose P P P high-energy bond Adenine + ribose + 3 phosphate groups The ATP ⇄ ADP cycle Energy is stored in the bonds between phosphate groups. ATP → ADP + Pᵢ releases energy (hydrolysis) ADP + Pᵢ → ATP stores energy (from respiration) Cells constantly recycle ATP — breaking off the third phosphate powers work, then it's rebuilt. ATP is the cell's "energy currency." Energy coupling: exergonic powers endergonic Exergonic reactions RELEASE free energy (−ΔG, spontaneous) e.g., ATP hydrolysis and the breakdown of glucose in respiration. Endergonic reactions REQUIRE energy input (+ΔG, non-spontaneous) e.g., building macromolecules. The cell couples them: energy from ATP hydrolysis drives the uphill reaction. Breaking ATP's third phosphate bond releases energy that powers the cell's uphill work. The Review Hub · AP Biology Unit 3 TOPIC 3.4 Photosynthesis 6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂ Light Reactions in the THYLAKOID membranes • Chlorophyll absorbs light energy • Water (H₂O) is split → releases O₂ • Electron transport chain pumps H⁺ • Produces ATP and NADPH Photosystems II & I capture light; the H⁺ gradient drives ATP synthase. Output: O₂ (waste), ATP + NADPH → Calvin Cycle in the STROMA (light-independent) • Uses the ATP & NADPH from stage 1 • CO₂ is "fixed" by the enzyme RuBisCO • Builds G3P → glucose (sugar) • Does NOT directly need light It runs on the chemical energy made in the light reactions, not on light itself. Output: glucose (stored energy) Where it happens: the chloroplast Light energy is converted into chemical energy stored in glucose. Autotrophs use this sugar to build all their organic molecules. Light reactions make ATP + NADPH (and O₂); the Calvin cycle uses them to build sugar. The Review Hub · AP Biology Unit 3 TOPIC 3.5 Cellular Respiration C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ~ATP (the reverse of photosynthesis) 1 · Glycolysis in the CYTOPLASM Glucose (6C) split into two pyruvate (3C). Net: 2 ATP + 2 NADH No oxygen required — this step is anaerobic. 2 · Krebs Cycle in the MITOCHONDRIAL MATRIX Pyruvate oxidized; CO₂ is released as waste. Makes 2 ATP + NADH + FADH₂ The electron carriers (NADH, FADH₂) feed stage 3. 3 · Electron Transport on the INNER MEMBRANE (cristae) NADH & FADH₂ drop electrons down the chain; H⁺ gradient drives ATP synthase. Makes ~28–34 ATP (most of it) O₂ is the FINAL electron acceptor → forms water. Without oxygen: fermentation If no O₂ is present, the electron transport chain stops. Cells fall back on glycolysis + fermentation, which regenerates NAD⁺ so glycolysis can keep making a small amount of ATP. Two types: lactic acid (muscle, bacteria) and alcoholic (yeast → ethanol + CO₂). Aerobic respiration yields far more ATP than fermentation. Respiration breaks glucose to make ATP; the electron transport chain produces the most, and needs O₂. The Review Hub · AP Biology Unit 3
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How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"

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This is great for review the night before the exam — fast, visual, and covers everything you need to remember about Unit 3's energetics.