#AP Biology: Cellular Energetics - Your Night-Before Review 🚀

Hey! Let's make sure you're feeling super confident about cellular energy. This guide is designed to be quick, clear, and exactly what you need tonight. Let's dive in!

#Unit 3: Energy and Metabolism

# 3.0 Introduction: Why Cells Need Energy

• Cellular energetics is all about how cells make, move, and use energy. Think of it as the cell's power grid! 💡
• Key processes: Cellular respiration (making ATP by breaking down glucose) and photosynthesis (making glucose using sunlight).
• ATP (adenosine triphosphate) is the cell's main energy currency. Everything we'll talk about is ultimately about making or using ATP.

# 3.1-3.3: Enzymes: The Cell's Catalysts

• Enzymes are protein catalysts that speed up reactions. They're essential for life! 🏃

• Active site: The specific spot on an enzyme where the substrate (reactant) binds. Think of it like a lock and key. 🔑

• Enzyme-substrate complex: When the substrate binds to the enzyme's active site.

• Denaturation: When an enzyme loses its shape and function due to factors like temperature or pH.

Caption: How enzymes work: substrate binding to the active site and product release.

• Environmental Factors: Temperature and pH affect enzyme activity. Each enzyme has an optimal range. 🌡️
• Substrate and Product Concentration: Too little substrate = slow reaction; too much product = inhibition.
• Inhibitors:
  • Competitive: Bind to the active site, blocking the substrate.
  • Noncompetitive: Bind to an allosteric site, changing the enzyme's shape.

# 3.4: Energy and Life

• Living systems need a constant energy input to maintain order. 🔄

• Entropy: The measure of disorder, which always increases in a closed system.

• Energy-releasing processes (like metabolism) are coupled with energy-requiring processes (like building molecules).

Caption: Energy flow in biological systems. Note the coupling of energy-releasing and energy-requiring processes.

• Sequential pathways: The product of one reaction becomes the reactant for the next (like a domino effect). This makes energy transfer efficient.

# 3.5: Photosynthesis: Capturing Light Energy

• Photosynthesis: The process of converting light energy into chemical energy (sugars). 🍭

• First evolved in prokaryotes (cyanobacteria), which oxygenated Earth's atmosphere.

• Light-dependent reactions: Capture light energy and convert it into ATP and NADPH.

Caption: Overview of the light-dependent and light-independent (Calvin Cycle) reactions of photosynthesis.

• Photosystems I and II: Embedded in chloroplast membranes, they absorb light and boost electrons to higher energy levels.
• Electron Transport Chain (ETC): Transfers electrons, creating a proton gradient across the membrane.
• ATP synthase: Uses the proton gradient to make ATP from ADP and inorganic phosphate. ➕
• Calvin cycle: Uses ATP and NADPH to convert CO2 into sugars (occurs in the stroma of the chloroplast).

# 3.6: Cellular Respiration and Fermentation: Getting Energy from Sugars

• Fermentation: An anaerobic process that produces ATP without oxygen (e.g., lactic acid or ethanol). 🍺

• Cellular respiration: An aerobic process that breaks down glucose to produce ATP using oxygen. Occurs in the mitochondria of eukaryotes.

• Terminal electron acceptor: Oxygen in aerobic respiration; other molecules in anaerobic respiration.

• Oxidative phosphorylation: The process of making ATP using the ETC and ATP synthase (in cellular respiration).

• Photophosphorylation: The process of making ATP using the ETC and ATP synthase (in photosynthesis).

Caption: Key steps of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport chain.

• Glycolysis: Breaks down glucose into pyruvate, producing ATP and NADH (occurs in the cytosol).
• Krebs cycle (citric acid cycle): Further oxidizes pyruvate, producing CO2, ATP, NADH, and FADH2 (occurs in the mitochondria).
• Electron Transport Chain (ETC): Transfers electrons, creating a proton gradient across the mitochondrial membrane. 😁
• ATP synthase: Uses the proton gradient to make ATP. 🌡️

# 3.7: Molecular Variation and Fitness

• Variation at the molecular level allows organisms to adapt to different environments. 💪
• Differences in molecules affect an organism's ability to survive and reproduce.

#Major Formulas

• Cellular Respiration: $C_6H_{12}O_6 + 6O_2 \rightarrow 6H_2O + 6CO_2$
• Photosynthesis: $6H_2O + 6CO_2 \rightarrow C_6H_{12}O_6 + 6O_2$
• Electron carriers: NADH, FADH2, NADPH (carry electrons in the form of hydrogen ions).
• ATP synthase: Enzyme that synthesizes ATP using chemiosmosis.

#Final Exam Focus 🎯

• High-Priority Topics: Photosynthesis, cellular respiration, enzyme function, and energy flow.
• Common Question Types: MCQs on enzyme inhibition, FRQs on comparing photosynthesis and respiration, and questions that combine multiple concepts (e.g., linking cellular respiration to the ETC and chemiosmosis).
• Time Management: Don't get bogged down on one question. If you're stuck, move on and come back later. Prioritize FRQs.
• Common Pitfalls: Confusing photosynthesis and respiration, not understanding enzyme inhibition, and missing the connection between the ETC and ATP synthesis.

#

Practice Question

Practice Questions

#Multiple Choice Questions

1. Which of the following best describes the role of an enzyme in a biochemical reaction? (A) It increases the activation energy of the reaction. (B) It decreases the activation energy of the reaction. (C) It is consumed during the reaction. (D) It changes the equilibrium of the reaction.

2. In cellular respiration, the primary role of oxygen is to: (A) Combine with carbon to form carbon dioxide. (B) Act as the final electron acceptor in the electron transport chain. (C) Combine with hydrogen ions to form water. (D) Provide the initial energy for glycolysis.

3. During photosynthesis, where does the Calvin cycle take place? (A) In the thylakoid membrane (B) In the stroma of the chloroplast (C) In the cytoplasm (D) In the inner mitochondrial membrane

#Free Response Question

Question:

Compare and contrast the processes of photosynthesis and cellular respiration in terms of their energy transformations, key reactants, products, and locations within the cell. Explain how the electron transport chain plays a role in both processes. (10 points)

Scoring Breakdown:

• (2 points): Correctly identify that both processes involve energy transformations. Photosynthesis converts light energy to chemical energy; cellular respiration converts chemical energy to ATP.
• (2 points): Correctly list key reactants and products for each process. Photosynthesis: reactants are CO2 and H2O, products are glucose and O2; Cellular respiration: reactants are glucose and O2, products are CO2 and H2O.
• (2 points): Correctly state the locations of each process. Photosynthesis: chloroplasts; Cellular respiration: cytoplasm (glycolysis) and mitochondria.
• (2 points): Accurately explain the role of the electron transport chain (ETC) in both processes. The ETC creates a proton gradient, which is used to generate ATP via ATP synthase.
• (2 points): Correctly identify the differences in the terminal electron acceptor in each process. Photosynthesis: NADP+; Cellular respiration: oxygen.

You've got this! Go get that 5! 💪