13 Turn over 6 Norovirus is a single-stranded RNA, non-enveloped virus. Norovirus is the most common cause of gastroenteritis. (a) The table shows some features used to classify viruses. Which box in each row shows how these viruses are classified? (3) Virus Classification of viruses DNA enveloped DNA non-enveloped RNA enveloped RNA non-enveloped Ebola λ (lambda) phage Tobacco mosaic 14 (b) One study into the causes of gastroenteritis involved 162 patients. This study found that 24.7% of these gastroenteritis cases were caused by viruses. The pie chart shows the proportion of the different types of virus identified as causing these gastroenteritis cases. astrovirus rotavirus A norovirus GI norovirus GII sapovirus rotavirus B both norovirus GI and GII Estimate the total number of gastroenteritis cases caused by noroviruses. (3) Answer .............................................................. 15 Turn over (c) Norovirus is usually spread through the faecal-oral route. The diagram shows the pathway that norovirus takes through the body. 1  The norovirus is transmitted in contaminated food or water. 2  The norovirus passes through the stomach and into the small intestine. 3  Some noroviruses are taken up by the cells of the small intestine. 4  Some noroviruses pass out of the body in the faeces. This process only takes a few hours. norovirus 1 2 3 4 Describe what happens inside the cells of the small intestine that have taken up the norovirus. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 16 (d) Noroviruses can infect an animal as individual viruses or as a cluster of viruses inside a lipid sphere. A cluster of viruses inside a lipid sphere is called a stealth sphere. The diagram shows a stealth sphere. lipid sphere enclosing noroviruses cluster of noroviruses (i) Animals infected with stealth spheres develop gastroenteritis very quickly and with severe symptoms. Animals infected with individual noroviruses develop gastroenteritis more slowly and with less severe symptoms. Analyse the information to explain these findings. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 17 Turn over (ii) Scientists are hoping that new treatments for norovirus infections can be developed to target the stealth sphere. Analyse the information to explain how targeting the stealth sphere could be used to treat these infections. 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(Total for Question 6 = 14 marks)