Biology & Life Sciences Chapter 17 Before The Animal Mounts Immune Response The

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CHAPTER 17 VIRUSES

Scientific Skills Exercise

Teaching objective: Students will use information from a phylogenetic tree to trace the

evolution of the H1N1 virus in the population of Taiwan.

Teaching tips: A version of this Scientific Skills Exercise can be assigned in MasteringBiology.

time walking the students through the structure of a tree. (For this purpose, the exercise refers

them to Figure 20.5.) The value of using a phylogenetic tree in combination with the graph for

this exercise is two-fold. First, by relating genetic change to time in the last few years, it

Note that the researchers analyzed 4,703 isolates, but there are only 36 variants shown in the

phylogenetic tree. This is because there are multiple isolates of each variant; i.e., the same

variant caused illne

each group of variants is represented by the number of isolates on the graph. The data do not

show the abundance of each individual isolate on the tree, as they are grouped in the graph.

Answers:

1. A/Taiwan1018/2011 and A/Taiwan/552/2011 are more closely related to each other than

A/Taiwan1018/2011 and A/Taiwan/8542/2009 because the branch length of the former pair,

from the point at which they separated from each other, is shorter compared to the length of the

Suggested Answers for End-of-Chapter Essay Questions

See the general information on grading short-answer essays and a suggested rubric at the

beginning of this document.

7. Scientific Inquiry

Each bacterium in the infected animal is capable of cell division by binary fission. Before the

animal mounts an immune response, the number of bacterial cells increases in an exponential

8. Focus on Evolution

absence of antiviral drugs, animal viruses exist in an environment where an immune system is

actively engaged in their recognition and elimination. RNA viruses are especially adept at

9. Focus on Organization

See the general information on grading short-answer essays and the suggested rubric at the

beginning of this document.

Sample key points:

Viruses consist of a nucleic acid surrounded by a protein coat (and, for animal viruses,

sometimes a viral envelope).

Sample top-scoring answer:

A virus has a very simple structure, well correlated with its function, which is to produce more

viruses. A virus consists of a nucleic acid, either DNA or RNA, surrounded by a protein coat.

10. Synthesize Your Knowledge

Neuraminidase is a molecule on the surface of the flu virus that acts as an enzyme to help release