Bacteria, viruses and infectionEdexcel International A Level Biology: Mind map

Exam questions on Bacteria, viruses and infection

1. A microbiologist is comparing the structure of three infectious agents: the bacterium Escherichia coli, tobacco mosaic virus (TMV) and human immunodeficiency virus (HIV). TMV is a rod-shaped virus with a single strand of RNA surrounded by a protein capsid. HIV has two strands of RNA inside a capsid, which is surrounded by a lipid envelope containing glycoproteins.
   Compare the structure of E. coli with the structure of TMV, giving two differences.2 marks
2. Bacteriophage lambda is a virus with a head, containing double-stranded DNA, and a tail with tail fibres. It infects the bacterium E. coli. In some infected bacteria the viral DNA is inserted into the bacterial chromosome and is copied each time the bacterium divides, without new phages being made. When these bacteria are later exposed to ultraviolet light, they burst open and release hundreds of new phages.
   Explain why exposing the bacteria to ultraviolet light leads to the release of new phages.2 marks
3. A man has had a persistent cough, with blood in his sputum, together with weight loss, fever and night sweats for six weeks. A sample of his sputum grew Mycobacterium tuberculosis, a bacterium with a waxy cell wall that contains mycolic acid. The bacteria were inhaled in droplets and reached the alveoli of the lungs, where they were engulfed by macrophages.
   Explain how Mycobacterium tuberculosis infects cells in the lungs and avoids destruction.3 marks