Respiration: The release of energy from food.

Aerobic respiration: The release of energy from food using oxygen.

Anaerobic respiration: The release of energy from food without oxygen.

Word Equation: Glucose + Oxygen —> (energy released) —> Carbon Dioxide + Water Vapour

Chemical Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Test:

• Limewater is a clear, colourless liquid.
• We exhale carbon dioxide.
• Blowing into limewater makes it turn cloudy or milky. Theory:

Role of CO₂ in respiration: When we breathe, our body uses oxygen and produces carbon dioxide as a waste product. This carbon dioxide is exhaled.

Using limewater to see CO₂: When you exhale into limewater, it reacts with the carbon dioxide in your breath. This reaction turns the limewater cloudy or milky, showing that carbon dioxide is present.

This simple test helps visually demonstrate that carbon dioxide is a by-product of the body's process of generating energy, i.e. a by-product of respiration.