A2.3:  Viruses

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How can viruses exist with so few genes?
• In what ways do viruses vary?

​
Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What mechanisms contribute to convergent evolution? (A2.3)
• To what extent is the natural history of life characterized by increasing complexity or simplicity? (A2.3)

Resources:

• ​Quizlet study set for this topic.  Coming soon!

AHL A2.3.1— Structural features common to viruses.

• List structural features common to all viruses. ​

AHL A2.3.2— Diversity of structure in viruses. 

• Outline the diversity of structure in viruses, including genetic material and the presence or absence of envelopes. 
• Distinguish between negative-sense RNA, positive sense RNA, retroviruses and DNA viruses.
• Compare the structure of bacteriophage lambda, coronaviruses and HIV.

AHL A2.3.3— Lytic cycle of a virus. 

• Outline the phases of the lytic cycle of a bacteriophage lambda virus.
• State that in the lytic cycle, a virus relies on a host cell for energy supply, nutrition, protein synthesis and other life functions.  ​

AHL A2.3.4— Lysogenic cycle of a virus.

• Compare the lytic system to the lysogenic cycle of a virus.  
• State that a temperate virus can alternate between a lytic and lysogenic cycle. 
• Outline the phases of the lysogenic cycle of a virus.

AHL A2.3.5— Evidence for several origins of viruses from other organisms.  

• Outline evidence that viruses evolved after the origin of cells.
• Outline the progressive and regressive hypotheses for the origin of viruses. 
• Outline how convergent evolution could result in the commonality of some structures shared by viruses.

AHL A2.3.6—  Rapid evolution in viruses. 

• Outline three reasons for rapid evolution in viruses. 
• Discuss the consequences of rapid virus evolution on treating diseases caused by viruses (influenza and HIV).