🧬 Metabolism and Energy: Vitamins
Grade 8 Biology — with Chemistry & Mathematics Connections
1. What Is Metabolism?
Think of your body as a complex chemical factory that runs 24/7. Even when you're sleeping, thousands of reactions are happening — your heart beats, your lungs breathe, your cells repair themselves. All of this requires energy, and virtually the only source of that energy is the food you eat.
⚡ Catabolism
Breaking down large molecules into smaller ones. This releases energy.
Example: Glucose is broken down during cellular respiration to release ATP.
🔧 Anabolism
Building up large molecules from smaller ones. This requires energy.
Example: Amino acids are assembled into proteins for muscle growth.
🔋 ATP — The Energy Currency
The body's energy currency is adenosine triphosphate (ATP) — an adenosine molecule with three phosphate groups attached. When one phosphate bond is broken, energy is released for the cell to use:
$\text{ATP} \rightarrow \text{ADP} + P_i + \text{Energy}$
🔥 2. Energy from Food — Calories & Macronutrients
🧪 Chemistry Connection: What Is a Calorie?
When we say a food has "200 Calories" on a nutrition label, we actually mean 200 kilocalories (kcal). Each "food Calorie" (capital C) = 1,000 scientific calories (lowercase c).
$1 \text{ food Calorie} = 1 \text{ kcal} = 1{}000 \text{ cal} = 4{}184 \text{ J}$
📊 Caloric Values of Macronutrients
| Macronutrient | Energy (kcal/g) | Energy (kJ/g) |
|---|---|---|
| 🍞 Carbohydrates | 4 | 16.7 |
| 🥩 Proteins | 4 | 16.7 |
| 🧈 Fats | 9 | 37.7 |