Diversity of organisms, classification and viruses

Learning objectives

Define a species as a group of organisms that can interbreed to produce fertile offspring, and discuss the difficulty of applying this definition to organisms that reproduce asexually and to populations separated in space or time

Describe variation between the individuals of a species, and explain how chromosome number and a karyotype can be used to identify a species and to detect chromosomal abnormalities

Describe the binomial system of naming and the hierarchy of taxa from domain to species, and explain why a natural classification groups organisms that share a common ancestor

(HL) Explain the division of living organisms into the three domains of bacteria, archaea and eukaryotes, using differences in ribosomal RNA sequences, membrane lipids and cell wall composition

(HL) Construct and interpret a cladogram from morphological or base sequence data, define a clade, use a molecular clock to estimate the time since two clades diverged, and explain why a group may be reclassified when new molecular evidence appears

(HL) Describe the structural diversity of viruses, including the protein capsid and a genome of either DNA or RNA, compare the lytic and the lysogenic cycles of a bacteriophage, and explain the rapid evolution of viruses such as influenza and HIV