Biology HL
Viral Structure and Life Cycles
- 1.
Compare a virus particle with a bacterial cell in terms of genetic material, protein synthesis and the production of new particles or cells. Explain why a virus cannot multiply on a sterile nutrient medium without suitable host cells.
[4 marks] · no calculator - 2.
After lambda bacteriophage infects a bacterium, one pathway rapidly produces phages and lyses the host; another integrates viral DNA into the host chromosome. Contrast the pathways and explain how the integrated viral DNA can persist through many bacterial generations before phage production resumes.
[4 marks] · no calculator - 3.
In a hypothetical influenza population, a pre-existing surface-protein variant is less strongly bound by antibodies than the common variant. Explain how its frequency could rise in an immune host population and why this does not mean antibodies deliberately induced a useful mutation.
[4 marks] · no calculator - 4.
In a hypothetical bacterial culture infected with lambda phage, some cells divide for many generations while carrying integrated phage DNA. After a DNA-damaging treatment, many cells produce phage particles and lyse. Distinguish the two stages and explain why phage DNA can be inherited before cell lysis occurs.
[4 marks] · no calculator - 5.
Two influenza strains infect the same host cell. Some offspring viruses contain genome segments from both strains. Explain how this can generate variation, distinguish it from a point mutation, and explain why it does not guarantee a successful new epidemic strain.
[4 marks] · no calculator - 6.
Two hypothetical viruses contain RNA in protein capsids. E also buds through a host-cell membrane and retains a lipid envelope with proteins needed for entry; N has no envelope. A supplied lipid-disrupting treatment is applied to particles, then removed before they contact healthy host cells. E's RNA remains detectable, but its infectivity falls sharply. Explain the source of E's envelope and why retaining RNA need not preserve infectivity. Explain why this result alone cannot show that N is unaffected, and identify a control addressing host-cell damage.
[5 marks] · no calculator