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Viruses and the Immune System
Essential knowledge 3.C.3: Viral replication results in genetic variation, and
viral infection can introduce genetic variation into the hosts.
a) Viral replication differs from other reproductive strategies and generates genetic variation
via various mechanisms.
Evidence of learning is a demonstrated understanding of each of the following:
1. Viruses have highly efficient replicative capabilities that allow for rapid evolution and
acquisition of new phenotypes.
2. Viruses replicate via a component assembly model allowing one virus to produce many
progeny simultaneously via the lytic cycle.
3. Virus replication allows for mutations to occur through usual host pathways.
4. RNA viruses lack replication error-checking mechanisms, and thus have higher rates of
mutation.
5. Related viruses can combine/recombine information if they infect the same host cell.
6. HIV is a well-studied system where the rapid evolution of a virus within the host
contributes to the pathogenicity of viral infection.
b) The reproductive cycles of viruses facilitate transfer of genetic information.
Evidence of learning is a demonstrated understanding of each of the following:
1. Viruses transmit DNA or RNA when they infect a host cell.
Examples include:
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Transduction in bacteria
Transposons present in incoming DNA
2. Some viruses are able to integrate into the host DNA and establish a latent (lysogenic)
infection. These latent viral genomes can result in new properties for the host such as
increased pathogenicity in bacteria.
KEY TERMS: pathogen, virus, bacteriophage, lytic pathway, lysogenic pathway, RNA, DNA,
HIV, retrovirus, protease, reverse transcriptase, CD4 receptor, integrase
Essential knowledge 2.D.4: Plants and animals have a variety of chemical
defenses against infections that affect dynamic homeostasis.
a) Plants, invertebrates and vertebrates have multiple, nonspecific immune responses.
Examples include:
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
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Invertebrate immune systems have nonspecific response mechanisms, but they lack
pathogen-specific defense responses.
Plant defenses against pathogens include molecular recognition systems with systemic
responses; infection triggers chemical responses that destroy infected and adjacent cells,
thus localizing the effects.
Vertebrate immune systems have nonspecific and nonheritable defense mechanisms
against pathogens.
b) Mammals use specific immune responses triggered by natural or artificial agents that disrupt
dynamic homeostasis.
Evidence of student learning is a demonstrated understanding of each of the following:
1. The mammalian immune system includes two types of specific responses: cell mediated
and humoral.
2. In the cell-mediated response, cytotoxic T cells, a type of lymphocytic white blood cell,
“target” intracellular pathogens when antigens are displayed on the outside of the cells.
3. In the humoral response, B cells, a type of lymphocytic white blood cell, produce
antibodies against specific antigens.
4. Antigens are recognized by antibodies to the antigen.
5. Antibodies are proteins produced by B cells, and each antibody is specific to a particular
antigen.
6. A second exposure to an antigen results in a more rapid and enhanced immune response.
✘Memorization of the structures of specific antibodies is beyond the scope of the course
and the AP Exam.
KEY TERMS: acquired immunity, antibody, antigen, antigen-MHC complex, apoptosis,
autoimmune disorder, B lymphocyte (B cell), cytotoxic T cell, helper T cell (CD4 lymphocyte),
histamine, immune system, inflammation, innate immunity, lymphatic system, lymph nodes,
macrophage, mast cell, MHC marker, natural killer cell, neutrophil, T lymphocyte (T cell), thymus