What hormones are involved in a pregnancy test and how does it work ? (6 marks)

After the human embryo implants in the uterus, the site of the developing placenta begins to produce a chemical called human chorionic gonadotrophin (hCG). hCG is a hormone that is found in the blood and urine of a mother. Pregnancy tests, test for hCG in the urine and rely on monoclonal antibodies. Monoclonal antibodies are antibodies produced to target particular cells or chemicals in the body. First, the wick of the pregnancy test is soaked in urine. The hCG molecules in the urine are carried up the test and they bind to mobile antibodies and form an hCG/antibody complex. This complex travels to the first 'window' of the pregnancy test and binds to immobilised antibodies arranged in a line that releases a coloured bead if the binding occurs. Here the first coloured line forms. The urine continues up the test to the second 'window'. Here excess mobile antibodies bind to immobilised antibodies and a coloured line will form regardless of whether the woman is pregnant or not. This line is a control. 2 coloured lines will show if the woman is pregnant and only one will if she is not.