A person first encounters antigen X on day 0. On day 40, the person encounters X again and antigen Y for the first time.
The table shows the responses following day 40.
Table
| Antigen | Time until antibody concentration starts increasing | Maximum antibody concentration in arbitrary units |
|---|---|---|
| X | 2 days | 160 |
| Y | 6 days | 25 |
Which explanation accounts for both differences?
Antibodies specific to X changed shape when Y entered the body.
Memory lymphocytes specific to Y were formed after the earlier exposure.
Antibodies specific to Y prevented lymphocytes responding to X from dividing.
Memory lymphocytes specific to X were formed after the earlier exposure.
87 exam-style questions on Edexcel GCSE Biology 5.3 Immune system and medicines, covering 5.3.1 The specific immune system, 5.3.2 Response to immunisation, 5.3.3 Advantages and disadvantages of immunisation, 5.3.4 Antibiotics and bacterial infections, 5.3.5 Aseptic techniques in culturing, 5.3.6 Cross-sectional areas of cultures, 5.3.7 Stages of developing new medicines, and 5.3.8 Production of monoclonal antibodies. Each one has a worked solution and a mark scheme showing where the marks go.