Effects of CO and nicotine on blood oxygen

Steps:

• Carbon monoxide binds to hemoglobin more strongly than oxygen, forming carboxyhemoglobin and reducing oxygen transport capacity.
• This binding decreases the overall concentration of oxygen in the blood.
• Nicotine stimulates the respiratory center in the brain, increasing breathing rate and oxygen intake.
• The faster breathing raises the partial pressure of oxygen, increasing its concentration in arterial blood short-term.

Why D is correct:

• D accurately states nicotine increases oxygen concentration via enhanced ventilation, while carbon monoxide decreases it by blocking hemoglobin's oxygen-binding sites.

Why the others are wrong:

• A incorrectly swaps the effects, claiming carbon monoxide increases oxygen.
• B reverses both: nicotine decreases oxygen (it increases), and carbon monoxide increases it (it decreases).
• C inverts the impacts, suggesting carbon monoxide boosts oxygen despite its competitive binding.

Final answer: D