Introduction (from Wikipedia). The Archaea constitute a domain or kingdom of single-celled microorganisms. These microbes are prokaryotes, meaning that they have no cell nucleus or any other membrane-bound organelles in their cells. Bacteria constitute a large domain of prokaryotic microorganisms.ut it was discovered that archaea have a distinct evolutionary history and biochemistry compared with bacteria. The similarities are that archaea and eubacteria are single-celled organisms that do not have a nucleus or organelles.
cohort noun [C ]. âº a âgroup of âpeople who âshare a characteristic, usually age: About 42% of women in this age cohort have a college degree. This year's cohort of âgraduates will have particular difficulties âfinding âjobs.ohort noun [C ]. âº a âgroup of âpeople who âshare a characteristic, usually age: About 42% of women in this age cohort have a college degree. This year's cohort of âgraduates will have particular difficulties âfinding âjobs.
1 It is a retrospective study. 2  This means that (like a detective) you begin at the end, with the disease, and then work backwards, to hunt for possible causes. 3  In our example, you could identify a group of patients with brain cancer (these would be the cases in case-control).here a cohort study is designed to identify causal factors for a disease, you would begin by selecting a sample of people who do not have the disease (so, prevalence = zero). You would then follow them over time. Some incident cases would arise, and these would provide you with an estimate of prevalence.