A student on a picnic to a park on a windy day stared sneezing and having difficulty in breathing on reaching the park. The teacher enquired whether the student was allergic to something. (a) What is an allergy?

a) The exaggerated response of the immune system to certain antigens present in the environment is called allergy. b) The system involved is the immune system. The unique characteristics are: (i) It recognizes foreign antigens and responds to them. (ii) It has memory and so it remembers antigens.