so far i have
Animals respire mostly by aerobic respiration. Aerobic respiration uses oxygen, taken from air and the cells produce energy which is used by these animals to live .When their respiratory system is not efficient, it means that they are not getting sufficient energy to live. So to get enough energy to survive, these large animals require efficient respiratory system.
and bigger animals need more oxygen to respire and they have a small volume sa to volume ratio
but i dont know if this would be accepted by the mark scheme as i dont have it for aqa