AQA GCSE Biology Paper 1 Practice Exam – Study Guide and Practice Test

When the hormone from the urine binds to the antibodies on the blue beads in a pregnancy test, it triggers a series of reactions that lead to the blue beads becoming immobilized on the test strip. The presence of the hormone indicates a positive result for pregnancy, and this binding event causes a visual change that turns the test strip blue, making it easy to interpret the results.

This process is part of an immunoassay method where the beads, coated with specific antibodies, capture the hormone if it is present, leading to a localized accumulation of the blue beads at the test site. Thus, the test strip displays a blue line, signifying that the hormone has been detected and confirming the pregnancy.