（b）Tuberculosis（TB）is an infectious disease that affects the human gas exchange system． The pathogen that causes TB secretes a protein that can be detected in saliva． Early diagnosis of TB is important in reducing the transmission of the pathogen． Scientists have developed a test strip for TB that uses monoclonal antibodies．Monoclonal antibodies are specific in their action． This test strip contains： －mobile monoclonal antibodies that bind to one part of the protein secreted by the pathogen －immobilised monoclonal antibodies． Fig． 3.2 shows a simplified diagram of the test strip． Fig． 3.2 A sample of saliva is collected and put onto the sample pad in the test strip． The saliva moves up the test strip through area 2. The mobile monoclonal antibodies are attached to tiny gold particles．If these antibodies collect in test area 3，a gold line becomes visible on the test strip． A gold line that becomes visible in area 4 confirms that the test strip is working and that the results are valid． （i）State the name of the pathogen that causes TB． ................................................................................................................................. （ii）Name the part of the monoclonal antibody that binds to the protein from the pathogen． ................................................................................................................................. ［1］ (iii) Saliva is added to a test strip to test for the presence of the protein secreted by the TB pathogen. Fig. 3.3 is a diagram showing some of the molecules in area 3 of the test strip when a positive result for TB is obtained. ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ................................................................................................................................. . The mobile monoclonal antibodies bound to tiny gold particles will bind to these immobilised monoclonal antibodies in area 4. If the test has functioned correctly, a gold line will be visible in area 4. Suggest how the structure of immobilised monoclonal antibodies in area 3 differs from the structure of the immobilised monoclonal antibodies in area 4. ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . .................................................................................................................................

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