The cells of smokers often use anaerobic respiration more than those of non-smokers.

Suggest one substance in cigarette smoke that may cause this.

[1 mark]

Explain why this substance has this effect.

[2 marks]

1) carbon monoxide

2) The respiratory system struggles to distribute air around the body because carbon monoxide deprives the blood cells of oxygen. This results in shortness of breath, particularly when undertaking strenuous activities.