This comprehensive study guide covers the key concepts of AP Biology Unit 3, focusing on cellular energetics. We'll delve into the intricacies of cellular respiration, fermentation, and photosynthesis, equipping you with the knowledge and understanding needed to excel in your studies. This guide is designed to be a valuable resource, supplementing your textbook and class notes.
I. Cellular Respiration: Harvesting Chemical Energy
Cellular respiration is the process by which cells break down glucose to produce ATP, the energy currency of the cell. This process occurs in three main stages: glycolysis, the Krebs cycle (citric acid cycle), and oxidative phosphorylation (electron transport chain and chemiosmosis).
A. Glycolysis: The First Steps
- Location: Cytoplasm
- Input: Glucose
- Output: 2 pyruvate, 2 ATP (net), 2 NADH
- Anaerobic Process: Does not require oxygen.
- Key Enzymes: Hexokinase, phosphofructokinase, pyruvate kinase (understanding the role of these enzymes is crucial).
B. Krebs Cycle (Citric Acid Cycle): Further Breakdown
- Location: Mitochondrial matrix
- Input: Pyruvate (converted to Acetyl-CoA)
- Output: 2 ATP, 6 NADH, 2 FADH2, CO2 (as a waste product)
- Decarboxylation: The release of carbon dioxide.
- Importance of Coenzyme A: Its role in acetyl-CoA formation.
C. Oxidative Phosphorylation: The Powerhouse
- Location: Inner mitochondrial membrane
- Electron Transport Chain (ETC): A series of protein complexes that transfer electrons, releasing energy.
- Chemiosmosis: The movement of protons (H+) across the inner mitochondrial membrane, generating a proton gradient that drives ATP synthesis via ATP synthase.
- ATP Synthase: The enzyme responsible for ATP production through chemiosmosis.
- Oxygen's Role: As the final electron acceptor in the ETC.
- Calculating ATP Yield: Understanding the approximate ATP yield from each stage of cellular respiration.
D. Comparing Aerobic and Anaerobic Respiration
This section should highlight the crucial differences in ATP production and the final electron acceptors.
II. Fermentation: Anaerobic Energy Production
Fermentation is an anaerobic process that allows cells to produce ATP in the absence of oxygen. There are two main types:
A. Lactic Acid Fermentation
- Products: Lactic acid and 2 ATP (per glucose molecule).
- Organisms: Muscle cells (during strenuous exercise), certain bacteria.
B. Alcoholic Fermentation
- Products: Ethanol, CO2, and 2 ATP (per glucose molecule).
- Organisms: Yeast and some bacteria.
C. Comparing Fermentation to Cellular Respiration
A detailed comparison of efficiency and end products is essential.
III. Photosynthesis: Capturing Light Energy
Photosynthesis is the process by which plants and other photosynthetic organisms convert light energy into chemical energy in the form of glucose. It occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle).
A. Light-Dependent Reactions: Capturing Light
- Location: Thylakoid membranes
- Photosystems: Photosystem II and Photosystem I (their roles and electron flow).
- Electron Transport Chain: Similar to cellular respiration, but using light energy to excite electrons.
- ATP and NADPH Production: The products of the light-dependent reactions, used in the Calvin cycle.
- Water Splitting: The source of electrons and oxygen.
B. Light-Independent Reactions (Calvin Cycle): Carbon Fixation
- Location: Stroma
- Carbon Fixation: The incorporation of CO2 into organic molecules.
- RuBisCo: The enzyme responsible for carbon fixation.
- G3P Production: The three-carbon sugar produced, used to synthesize glucose.
- ATP and NADPH Consumption: The energy sources for the Calvin cycle.
C. Factors Affecting Photosynthesis
Environmental factors like light intensity, carbon dioxide concentration, and temperature should be examined.
D. C3, C4, and CAM Plants
Explain the adaptations of these plants to different environmental conditions.
IV. Connecting Cellular Respiration and Photosynthesis
Explain the cyclical relationship between these two processes, emphasizing the flow of energy and matter.
This study guide provides a framework for your review. Remember to consult your textbook, class notes, and practice problems to solidify your understanding of these crucial concepts. Good luck with your AP Biology exam!
