The immune response — CCEA AS Biology Practice Questions

Question 1

Describe how the body produces a specific immune response following infection by a pathogen.

Accepted Answer

A phagocyte engulfs the pathogen by phagocytosis and displays the pathogen's antigens on its own cell surface membrane, becoming an antigen-presenting cell. A T helper cell with a receptor complementary to that antigen binds to it and releases cytokines, which activate the specific B lymphocyte that also has a complementary receptor — clonal selection. That B lymphocyte divides repeatedly by mitosis to form a clone. Most of these differentiate into plasma cells, which secrete large quantities of a specific antibody that is complementary to the antigen and causes agglutination of the pathogen. Some become memory cells, which remain in the blood so that on re-infection with the same pathogen antibodies are produced faster and in greater quantity — the secondary response.

Question 2

Explain why vaccination against influenza is needed each year, whereas a single course of vaccination against measles gives long-lasting protection.

Accepted Answer

The influenza virus mutates frequently, which changes the shape of its surface antigens — antigenic variability. Memory cells and antibodies produced against last year's strain are no longer complementary to the new antigens, so they cannot bind and no rapid secondary response occurs. A new vaccine matched to the circulating strains is therefore needed each year. The measles virus shows very little antigenic variation, so the memory cells formed after vaccination remain complementary to its antigens and continue to give a rapid secondary response for many years.

The immune response: CCEA Biology practice questions

Sit the questions

Describe how the body produces a specific immune response following infection by a pathogen.

Read the full walkthrough

More practice sets