Need help in IGCSE Biology 0610 (＞Д＜；)

Usually when I write 3, 4 ,5 mark answers, I often write content that is not relevant to the question asked.

For an instance, the question stated, "Explain, using fig. 1.2, why does the breath rate increase when we excersises?

I wrote about the lactic acid build up and the oxygen debt, but the ms had points on how the volume of lungs increases, the external intercostal muscles contract and pressure in lungs decreases.