Chapter 7 : Metabolism

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Chapter Overview & SLOs

What is metabolism? Chapter 7, "Metabolism," explores how living organisms acquire, transform, and utilize energy to sustain life. This chapter answers fundamental questions about the chemical processes that occur within living organisms. What are enzymes and how do they work? You will learn about enzymes - protein-based biological catalysts that accelerate chemical reactions by lowering activation energy. The chapter covers: - Characteristics of enzymes: Specificity (each enzyme acts on a specific substrate), sensitivity to temperature and pH, catalytic efficiency (can be reused), and requirement of cofactors. - Cofactors: Non-protein components required for enzyme activity including activators (inorganic ions like Mg2+, Zn2+), prosthetic groups (tightly bound organic molecules like heme), and coenzymes (loosely bound organic molecules like NAD+, FAD). - Lock and Key Model: Active site of enzyme has a fixed shape complementary to substrate. - Induced Fit Model: Active site changes shape upon substrate binding, creating a perfect fit. - Factors affecting enzyme activity: pH (pepsin works best at pH 1.5-2.5, trypsin at pH 7.5-8.5), temperature (optimum around 37°C for human enzymes, denaturation above 50-60°C), substrate concentration (increases activity until saturation), and enzyme concentration. What is ATP and why is it important? You will study the structure and function of ATP (Adenosine Triphosphate) - the energy currency of the cell: - Structure: Adenine + Ribose (adenosine) + Three phosphate groups - ATP-ADP Cycle: When ATP is broken down to ADP + inorganic phosphate (Pi), energy is released (7.3 kcal/mol) for cellular work. This energy powers active transport, muscle contraction, nerve impulse transmission, and biosynthesis. What is photosynthesis and how does it work? The chapter provides a detailed explanation of photosynthesis - the process by which plants convert light energy into chemical energy: - Light-dependent Reactions: Occur in thylakoid membranes. Chlorophyll absorbs light energy, water undergoes photolysis (splitting into H+, electrons, and O2), ATP and NADPH are produced. Oxygen is released as a byproduct. - Dark Reactions (Calvin Cycle): Occur in the stroma. CO2 is fixed into organic molecules using ATP and NADPH from light reactions. Glucose is synthesized as the final product. - Factors limiting photosynthesis: Light intensity, carbon dioxide concentration, temperature, and water availability. - Net equation: 6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2 What is cellular respiration and how does it differ from photosynthesis? You will compare: - Aerobic Respiration: Requires oxygen. Complete breakdown of glucose into CO2 and H2O, producing 36-38 ATP molecules per glucose. Net equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP - Anaerobic Respiration (Fermentation): Occurs without oxygen. Incomplete breakdown of glucose producing: - Alcoholic Fermentation: Produces ethanol + CO2 + 2 ATP. Used in baking (bread rising), brewing (beer, wine), and biofuel production. - Lactic Acid Fermentation: Produces lactic acid + 2 ATP. Occurs in muscles during intense exercise (causing cramps) and in yogurt/production (fermented dairy). What is the economic importance of fermentation? You will learn practical applications including baking (CO2 causes dough to rise), brewing (production of alcoholic beverages), dairy (yogurt, cheese production), and biofuel (ethanol production from corn/sugarcane). These notes are strictly aligned with the Student Learning Outcomes (SLOs) for the FBISE 2026 annual examination.

• What are enzymes and their characteristics? Define enzymes as biological catalysts and explain their characteristics including specificity, sensitivity, and catalytic efficiency, including the roles of cofactors like activators (inorganic ions), prosthetic groups (tightly bound organic molecules), and coenzymes (loosely bound organic molecules like NAD+).
• What is ATP and why is it the energy currency? Describe the structural components of ATP (adenine + ribose + three phosphates) and explain why it is considered the universal energy currency for cellular work, including the ATP-ADP cycle and energy release of 7.3 kcal/mol.
• What are the mechanisms of photosynthesis? Explain the mechanisms of photosynthesis, identifying the reactants (CO2, H2O, light) and products (glucose, O2) of light-dependent reactions (thylakoids, water photolysis, ATP and NADPH production) and dark reactions (Calvin cycle in stroma, CO2 fixation), and describe the factors that limit their rate including light intensity, CO2 concentration, and temperature.
• What are the differences between aerobic and anaerobic respiration? Differentiate between aerobic respiration (requires oxygen, produces 36-38 ATP, complete breakdown) and anaerobic respiration (no oxygen, produces 2 ATP, incomplete breakdown), and discuss the significance of fermentation including alcoholic fermentation (ethanol + CO2) and lactic acid fermentation (lactic acid) in daily life and industrial applications like baking, brewing, and dairy production.

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