This comprehensive study guide covers all the key concepts in AP Biology Unit 7, focusing on cellular respiration and fermentation. We'll break down the complex processes, highlight crucial connections, and provide strategies for mastering this vital unit. Remember to consult your textbook and class notes for additional details and examples.
I. Cellular Respiration: Harvesting Energy from Glucose
Cellular respiration is the process by which cells break down glucose to generate ATP, the cell's primary energy currency. This process is remarkably efficient, extracting a significant portion of the energy stored within glucose molecules.
A. Glycolysis: The First Steps
- Location: Cytoplasm
- Net Products: 2 ATP (net gain), 2 NADH, 2 pyruvate molecules
- Key Enzymes: Hexokinase, Phosphofructokinase, Pyruvate Kinase (these are often targets for regulation).
- Anaerobic Process: Glycolysis occurs whether oxygen is present or not.
B. Pyruvate Oxidation: Preparing for the Krebs Cycle
- Location: Mitochondrial matrix
- Products (per pyruvate): 1 NADH, 1 CO2, Acetyl-CoA
- Decarboxylation: A crucial step where a carbon atom is removed as CO2.
C. Krebs Cycle (Citric Acid Cycle): Central Metabolic Hub
- Location: Mitochondrial matrix
- Products (per acetyl-CoA): 3 NADH, 1 FADH2, 1 ATP (GTP), 2 CO2
- Cyclic Process: The cycle regenerates oxaloacetate, allowing it to continue.
- Role in Anabolism: Intermediates of the Krebs cycle are used in other biosynthetic pathways.
D. Oxidative Phosphorylation: ATP Synthesis
- Location: Inner mitochondrial membrane
- Electron Transport Chain (ETC): Electrons from NADH and FADH2 are passed along a series of protein complexes, releasing energy used to pump protons (H+) into the intermembrane space.
- Chemiosmosis: The proton gradient generated by the ETC drives ATP synthesis via ATP synthase.
- Oxygen's Role: Oxygen acts as the final electron acceptor, forming water. Without oxygen, the ETC stops, significantly reducing ATP production.
- ATP Yield: Oxidative phosphorylation generates the vast majority of ATP produced during cellular respiration (around 32-34 ATP per glucose molecule).
II. Fermentation: Anaerobic ATP Production
Fermentation is an anaerobic process that allows cells to generate ATP in the absence of oxygen. While less efficient than cellular respiration, it provides a crucial alternative pathway for energy production.
A. Lactic Acid Fermentation
- Products: 2 lactic acid molecules, 2 ATP (from glycolysis only)
- Organisms: Muscle cells (during strenuous exercise), some bacteria
B. Alcoholic Fermentation
- Products: 2 ethanol molecules, 2 CO2, 2 ATP (from glycolysis only)
- Organisms: Yeast, some bacteria
III. Regulation of Cellular Respiration
The rate of cellular respiration is tightly regulated to meet the cell's energy demands. Key regulatory points include:
- Glycolysis: Phosphofructokinase is a crucial regulatory enzyme.
- Citric Acid Cycle: Several enzymes are regulated by the availability of substrates and energy levels.
- Allosteric Regulation: Many enzymes are regulated by allosteric effectors (molecules that bind to the enzyme and alter its activity).
- Feedback Inhibition: The final products of the pathway can inhibit earlier steps in the process.
IV. Connections to Other Metabolic Pathways
Cellular respiration is intricately connected to other metabolic pathways, including:
- Photosynthesis: The products of photosynthesis (glucose and oxygen) are the reactants for cellular respiration.
- Lipid and Protein Metabolism: Lipids and proteins can be broken down and their components fed into cellular respiration.
V. Study Strategies for AP Success
- Practice diagrams: Draw out the pathways of glycolysis, pyruvate oxidation, the Krebs cycle, and oxidative phosphorylation. Label all the reactants, products, and key enzymes.
- Master the energetics: Understand the net ATP production at each stage and the overall ATP yield of cellular respiration.
- Compare and contrast: Differentiate between aerobic respiration and fermentation. Compare the different types of fermentation.
- Focus on regulation: Understand how the rate of cellular respiration is controlled.
- Practice, practice, practice: Work through practice problems and past AP exam questions.
By diligently studying these key concepts and employing effective study strategies, you can confidently tackle the AP Biology Unit 7 exam and achieve a strong understanding of cellular respiration and fermentation. Remember that consistent effort and a thorough understanding of the underlying principles are key to success.
