5.1. Enzymes
A subsection of Biology, 0610, through 5. Enzymes
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For Examiner's Use Enzymes are biological catalysts. Define the term catalyst. Urease is an enzyme found in bacteria and in the seeds of some species of bean. The enzyme catalyses the reaction: urea + water carbon dioxide + ammonia The production of ammonia increases the pH of the area around the bacteria. The formation of ammonia can be used to study the progress of the reaction by testing the pH of the surrounding medium with a pH indicator, such as Universal Indicator solution. Some students carried out an investigation to find out if there was urease in the seeds of four different species of bean. • The germinating seeds were ground up in water and filtered to give an extract containing proteins. • Each extract was added to a urea solution and kept at 30 °C for 30 minutes (tubes 1 to 4). • Two more tubes (5 and 6) were included in the investigation. • Samples were taken from the reaction mixture at five-minute intervals and tested with Universal Indicator solution. The results are shown in Table 4.1. Table 4.1 presence of alkaline pH at intervals of 5 minutes test-tube bean species urea solution water soya yes no        mung yes no        jack yes no        broad yes no        soya no yes        no beans yes yes         = alkaline pH  = not alkaline pH For Examiner's Use Explain why the test-tubes were kept at 30 °C. Explain why test-tubes 5 and 6 were included in the investigation. State the conclusions that the students would make from the results of test-tubes 1 to 4. It is thought that some bean seeds produce ammonia as a protection against infection by microorganisms in the soil. Suggest what would happen to any ammonia that passes into the soil. For Examiner's Use Helicobacter pylori is a bacterium that infects the stomach and causes ulcers. The bacteria secrete urease that helps them to colonise the stomach lining. Explain why bacteria do not usually grow inside the stomach. Suggest how urease helps the bacteria to colonise the stomach. Explain how the immune system protects against infection by bacteria such as H. pylori.
0610_w12_qp_32
THEORY
2012
Paper 3, Variant 2
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Questions Discovered
248