(i) The significance of the reflex arcs is their efficiency that they exhibit during quick responses. Reflex arc work as a very efficient method whenever we lack the true thinking processes. 

(ii) The significance of reflex action is the protection that we get due to reflex action against any stimulus. Reflex actions are quick responses that we give against any stimulus which can cause harm to us. If we don’t have such quick responses we may get armed badly. For example- If someone touches a flame and does not exhibit any quick response due to reflex action then that particular person will definitely get burnt as thinking processes and then giving a response are not so fast processes and provide enough time for harm. 

(iii) Adrenaline hormone is the stress hormone. Due to the release of this hormone our heart starts beating faster due to which more blood is supplied to the muscles, Supply of blood is diverted from digestive system, skin to the muscles, breathing rate is also increased. Due to all this our body gets prepared to deal with that stressful situation and help us to decide whether we are going to fight the situation with the complete energy or will flight from there utilizing the energy produced due to release of stress hormone. 

Basically, we can say that this hormone helps us to deal to difficult stressed situations.