Respiration

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$

• Uses oxygen
• Occurs in mitochondria
• Produces lots of energy (ATP)
• Continuous process in all living cells

Without oxygen (e.g. during intense exercise):

In animals: $\text{glucose} \rightarrow \text{lactic acid}$

In yeast/plants: $\text{glucose} \rightarrow \text{ethanol} + \text{carbon dioxide}$ (This is fermentation — used in bread and beer making)

• Much less energy released than aerobic
• Lactic acid causes muscle fatigue and cramp

During exercise:

• Heart rate increases → more blood to muscles
• Breathing rate and depth increase → more O₂ in, more CO₂ out
• Glycogen broken down to glucose in muscles

During intense exercise:

• Muscles can't get enough O₂ → anaerobic respiration
• Oxygen debt: extra oxygen needed after exercise to break down lactic acid
• Lactic acid transported to liver → converted back to glucose

The sum of all chemical reactions in an organism.

Examples of metabolic reactions:

• Aerobic and anaerobic respiration
• Photosynthesis
• Synthesis of proteins from amino acids
• Breakdown of excess amino acids (deamination in liver)
• Synthesis of lipids from fatty acids and glycerol

• Aerobic: glucose + O₂ → CO₂ + H₂O (in mitochondria; lots of energy)
• Anaerobic: glucose → lactic acid (animals) or ethanol + CO₂ (yeast)
• Oxygen debt: extra O₂ to break down lactic acid after exercise
• Metabolism: all chemical reactions in an organism