Question

A student on a picnic to a park on a windy day started sneezing and having difficulty in breathing on reaching the park. The teacher enquired whether the student was allergic to something.
What is an allergy? Write the two unique characteristics of the system involved in response observed in the student?

Answer 1

Hint: Anton Van Pirke coined the term allergy to describe any change in the body's ability to react to foreign substances. It has now been found that this phenomenon is mediated by the body's immune response. However, if the immunological causes damage the cells of the body, people talk about hypersensitivity. Today, the two terms allergy and hypersensitivity are used synonymously.

Complete answer:
Allergies are dangerous immune responses caused by antigens that are actually harmless. Allergies are caused by certain biological and abiological agents present in the atmosphere. The agents that cause allergies that are in the air are called aeroallergens, and the allergies they cause are called aeroallergens. Some of the well-known aeroallergens are house dust, pollen, cosmetics, microbial spores or cells, and many more.
2) For answering the second part of the question let’s first look at the mechanism of allergic reaction.
Antibodies are produced by antibody-producing cells from the lymphoid tissue of allergic individuals in response to initial exposure to allergens (proteins).
These IgE antibodies circulate in the serum in the blood and attach to the surface of mast cells or basophils.
The Mast cells are rich in granules containing histamine and various other biologically active substances such as bradykinin, prostaglandin, and others. When certain allergens (of the same pollen type) reappear later (second exposure), they bind to adjacent pairs of IgE molecules on the mast cell surface.
This binding interaction causes the rapid release of tissue mediators, especially histamine, from the granules secreted by mast cells.
So we arrived at the conclusion that during allergic reaction two characteristics reaction that occur is:
Production of IgE antibodies and secretion of histamine and serotonin from mast cells.

Note: 

Asthma: Asthma can be allergic or non-allergic in nature. In allergic asthma, the surrounding allergens such as pollen and spores cause disease through inhalation. Sufferers may experience seizures that block the flow of air to the lungs due to swelling of the lining and the formation of phlegm in that lining.
Rhinitis: This is a type of perennial allergy. Symptoms are similar to fever but occur throughout the year. This condition is caused by non-seasonal allergens such as pollen from grasses and other plants that bloom throughout the year.
Conjunctivitis: People are more likely to suffer from allergic eye disease than adults. Allergic conjunctivitis is often associated with allergic rhinitis.
Hay fever: This is a type of seasonal allergy. Pollen grains from some grasses, weeds, and trees are the main cause of this type of allergy, although mold spores can also cause symptoms.