Question

Suggest how damage to the air sacs can cause the symptom of breathless when exercising.

Answer 1

Let's say you're exercising. You can exercise normally, going at a good-enough base to not overwork. Now, let's just say you start to overwork, for a couple of hours. You do this for a period of time, constantly.

Doing this all has now caused damage to your air sacs. While overworking while exercising again, (after having done it for a long time) you get the symptom of breathlessness.
Breathless symptoms can be shortness of breath/difficulty while breathing, increase in pulse rate, showing signs of pale skin, and chest pain. You got this symptom from overworking, which lead to the damage in your air sacs.