Metabolism and Energy in the Body - Revision Sheet

1. 📌 Essentials

• ATP is the main energy currency in cells, composed of adenine, ribose, and three phosphate groups. Cellular metabolism is divided intoabolism (energy release) and anabolism (energy consumption).
• Photosynthesis converts light energy into chemical energy in autotrophs; respiration releases energy from glucose.
• Autotrophs produce organic molecules from inorganic substances; heterotrophs consume organic matter.
• Digestion breaks down macromolecules into absorbable monomers.
• Energy flow in ecosystems moves from autotrophs to heterotrophs via food chains.
• Hydrolysis of ATP releases energy necessary for cellular processes.
• Fermentation is an anaerobic pathway producing small amounts of ATP.
• Vitamins act as cofactors for enzymatic reactions in metabolism.
• Nutrients are classified into energetic (carbohydrates, lipids, proteins) and non-energetic (vitamins, minerals, water).

2. 🧩 Key Structures & Components

• ATP (Adenosine Triphosphate) — energy molecule; structure: adenine + ribose + 3 phosphate groups.
• Mitochondria — site of cellular respiration and ATP production.
• Chloroplasts — site of photosynthesis in autotrophs.
• Enzymes — proteins that catalyze metabolic reactions, often requiring vitamins as cofactors.
• Macromolecules — carbohydrates, lipids, proteins, nucleic acids.
• Digestive system — organs involved in breaking down food: mouth, stomach, intestines.
• Food chain — transfer of energy from producers to consumers.

3. 🔬 Functions, Mechanisms & Relationships

• ATP hydrolysis (ATP → ADP + Pi + energy) fuels cellular activities.
• Photosynthesis (in chloroplasts): light energy → chemical energy (glucose).
• Cellular respiration (in mitochondria): glucose + oxygen → ATP + CO₂ + H₂O.
• Fermentation occurs when oxygen is scarce, producing ATP anaerobically.
• Nutrients are absorbed as monomers: monosaccharides, amino acids, fatty acids.
• Autotrophs form the base of food chains, supporting heterotrophs.
• Enzymes require cofactors (vitamins) to catalyze metabolic reactions.
• Energy transfer is unidirectional: autotrophs → heterotrophs.

4. Comparative Table

5. 🗂️ Hierarchical Diagram

Metabolism and Energy
 ├─ ATP
 │   └─ Main energy molecule; hydrolysis releases energy
 ├─ Metabolic Pathways
 │   ├─ Catabolism: breakdown, energy release
 │   └─ Anabolism: synthesis, energy consumption
 ├─ Photosynthesis
 │   └─ Light energy → glucose in autotrophs
 ├─ Cellular Respiration
 │   └─ Glucose oxidation → ATP, CO₂, H₂O
 ├─ Digestion
 │   └─ Macromolecules → Monomers
 ├─ Nutrients
 │   ├─ Energéticos: carbs, lipids, proteins
 │   └─ Não energéticos: vitamins, minerals, water
 └─ Energy Flow
     └─ From autotrophs to heterotrophs via food chains

6. ⚠️ High-Yield Pitfalls & Confusions

• Confusing ATP hydrolysis with synthesis; hydrolysis releases energy.
• Misidentifying the site of photosynthesis (chloroplasts) vs. respiration (mitochondria).
• Overlooking the role of enzymes and cofactors in metabolic reactions.
• Assuming fermentation produces large ATP amounts; it produces minimal ATP anaerobically.
• Confusing autotrophs (produce their own food) with heterotrophs (consume organic matter).
• Mistaking the energy flow direction in food chains; always from producers to consumers.
• Ignoring that vitamins are cofactors, not direct energy sources.
• Overgeneralizing digestion; specific enzymes target specific macromolecules.

7. ✅ Final Exam Checklist

• Know the structure and function of ATP.
• Understand the difference between catabolism and anabolism.
• Be able to write and interpret the photosynthesis and respiration equations.
• Recognize the main sites of cellular respiration and photosynthesis.
• Explain the process and significance of fermentation.
• Distinguish autotrophs from heterotrophs.
• Describe the stages of digestion and nutrient absorption.
• Identify key nutrients: energetic vs. non-energetic.
• Understand energy flow in ecosystems.
• Know the role of enzymes and cofactors in metabolism.
• Be familiar with the main macromolecules involved in energy metabolism.
• Understand the hierarchical organization of metabolic pathways.
• Recognize common pitfalls and clarify misconceptions.
• Be able to interpret simple diagrams of metabolic pathways and energy flow.