Edexcel iGCSE Biology-2.34 process of respiration- Study Notes- New Syllabus

Respiration – Producing Energy (ATP) in Living Organisms

📝 Introduction

All living organisms need energy to:

• Grow
• Move
• Maintain body functions
• Carry out chemical reactions

Energy is obtained from food molecules (mainly glucose) through respiration.
ATP (Adenosine Triphosphate) = energy currency of the cell.

🔑 What is Respiration?

Definition: Respiration is the chemical process that breaks down glucose (or other nutrients) to release energy in the form of ATP.

Two main types:

– Aerobic respiration (with oxygen)

– Anaerobic respiration (without oxygen)

⚙️ Aerobic Respiration

Equation: 

Word equation: Glucose + Oxygen → Carbon dioxide + Water + Energy

Chemical equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

Where it happens: Mainly in mitochondria of cells.

ATP yield: ~36–38 ATP molecules per glucose molecule.

• Requires oxygen.
• Produces CO₂ and H₂O as waste products.
• Very efficient → produces lots of energy.

⚙️ Anaerobic Respiration

Word equation (humans): Glucose → Lactic acid + Energy

Word equation (plants & yeast): Glucose → Ethanol + Carbon dioxide + Energy

Where it happens: Cytoplasm of cells.

ATP yield: Only ~2 ATP per glucose molecule → much less than aerobic.

• Occurs when oxygen is insufficient (e.g., intense exercise).
• Produces lactic acid in humans → causes muscle fatigue.
• Produces ethanol + CO₂ in yeast → used in fermentation.

📊 Summary Table

⚡ Quick Recap 
Respiration → ATP → energy for all life processes.
Aerobic = glucose + O₂ → CO₂ + H₂O + lots of ATP.
Anaerobic = glucose → lactic acid (humans) or ethanol + CO₂ (plants/yeast) → little ATP.
Location: Mitochondria (aerobic), Cytoplasm (anaerobic).