Describe the biological species concept.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2022). The mark or mark type is shown in brackets.

1. [3] 1 individuals (within a population) can, breed / mate / reproduce ; 2 to produce fertile offspring; 3 are reproductively isolated (from other species) / AW;
2. [1] any one from: 1 for organisms that, do not breed sexually / are asexual; 2 for, fossil / extinct, organisms ; 3 morphological differences are easier to determine ; 4 often not possible to observe reproductive behaviour ; 5 time required for mating behaviour may take too long (to be observed) / not possible to achieve conditions in which mating can occur (while being observed) ;
3. [4] any four from: max three: 1 both are prokaryotes or both have no, nucleus / (double) membrane-bound organelles ; 2 both have circular DNA; 3 both have 70S ribosomes ; 4 both reproduce by, binary fission / budding / fragmentation ; max three: 5 bacteria cell wall made of peptidoglycan whereas Archaea cell wall does not have peptidoglycan ; 6 bacteria cell membrane has ester-linked lipids whereas Archaea cell membrane has ether-linked lipids ; 7 have different ribosomal RNA ; 8 Bacteria do not have (DNA associated with) histones whereas Archaea do have (DNA associated with) histones ; 9 Bacteria form spores whereas Archaea do not form spores ;