IB Biology A2.3 Definitions
This page contains our IB Biology definitions for A2.3. By learning each one of these definitions, you will fully cover the content for IB Biology 'Viruses'.
Acellular
Not consisting of, divided into, or containing cells
Antigenic Drift
Small mutations that accumulate over time in a virus's surface antigens, leading to immune system evasion
Antigenic Shift
The process by which two or more different viruses or different strains infect the same cell and create a novel subtype
Escape Hypothesis
The theory that viruses evolved from genetic material released from the genes and encapsulated in the proteins of larger organisms
gene expression
The conversion of genes to proteins to express the gene's coded characteristic
genome
All the genes in an organism
HIV
A infection that is notoriously difficult to treat beause it infects lymphocytes involved in antibody production and can destroy them over time, preventing antibody production
Inert
Lacking the ability to move or function independently
Lysogenic Cycle
A viral replication cycle where the viral DNA integrates into the host cell's genome, replicates along with the host cell, and can eventually switch to the lytic cycle
Lytic Cycle
A viral replication cycle where the virus attaches to the host cell, injects its genome, replicates using the host's machinery, assembles new viruses, and kills the host cell to release the new viruses
metabolism
The sum of all chemical reactions taking place within an organism
mutation
A random change to the base sequence of a gene
pathogen
An organism or virus that causes a disease
Regressive Hypothesis
The theory that viruses were once small cells that were parasites in larger cells and over time lost the genes not required, becoming fully dependent on host cells
Retroviral Activity
The replication process of retroviruses, like HIV, which reverse transcribe their RNA into DNA to integrate into the host genome
Virus-first Hypothesis
The theory that viruses evolved at the same time as the first cells and have been dependent on them since the beginning
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