Answer:
Less air sacs or surface area = less gas exchage = less oxygen makes it to the blood
Step-by-step explanation:
Well, smoking is very bad cuz it basically breaks down your alveoli (air sacs) and causes their wall to be so thin that they start to merge with each other. Merging lowers the available surface area in lung for gas exchange, thus you cannot exchage the oxygen from your lung into the blood. Even though when you breathe in you take in all the oxygen you possibly can, it does not matter cuz it won't be making it to your blood as efficiently.