Explain the role of the specific immune system of the human body in…

The idea

When a pathogen enters the body, the person is exposed to it. The pathogen carries antigens on its surface, which are molecules the immune system recognises as foreign. These antigens trigger an immune response: lymphocytes produce antibodies that are specific to the antigen and bind to it, helping to destroy the pathogen. The same antigens also trigger the production of memory lymphocytes, which remain in the body after infection. If the same antigen is encountered again, memory lymphocytes respond quickly and in large numbers, producing antibodies faster and in greater quantity. This is the secondary response, which usually prevents illness on re-exposure.

What earns the marks

• Exposure to a pathogen introduces foreign antigens into the body.
• Antigens on the pathogen trigger an immune response.
• The immune response causes lymphocytes to produce antibodies specific to the antigen.
• Antibodies bind to antigens to help destroy the pathogen.
• Antigens also trigger the production of memory lymphocytes.
• Memory lymphocytes remain after infection and give a faster, larger secondary response on re-exposure to the same antigen.

Common mistakes and how to put them right

• Saying antibodies are produced by the pathogen.

  Put it right: Antibodies are produced by the body's lymphocytes in response to antigens.

• Confusing antigens and antibodies.

  Put it right: Antigens are on the pathogen surface; antibodies are proteins produced by the body that bind to antigens.

• Thinking memory lymphocytes act in the first exposure.

  Put it right: Memory lymphocytes mainly act in the secondary response on re-exposure.

Exam tips

• Use the sequence: exposure → antigens → immune response → antibodies and memory lymphocytes → secondary response.
• State that antibodies are specific to the antigen to gain precision marks.
• Explain the secondary response as faster and producing more antibodies, not just 'stronger'.