Quick questions on Cell theory, prokaryotic and eukaryotic cells (QCE Biology Unit 1)

The modern cell theory has three core postulates:

Prokaryotes are unicellular organisms whose genetic material is not enclosed in a nucleus. They fall into two domains:

Eukaryotes have a true membrane-bound nucleus containing linear chromosomes wrapped around histone proteins. They include all animals, plants, fungi and protists.

Eukaryotes can be larger because they compartmentalise functions into organelles, increasing internal membrane surface area for reactions. Prokaryotes rely on diffusion across the plasma membrane, which limits their size (see surface area to volume ratio).

Mitochondria and chloroplasts have their own circular DNA, 70S ribosomes and double membranes, and divide by binary fission. The endosymbiotic theory proposes that they originated from free-living bacteria engulfed by an ancestral eukaryotic cell. This is consistent with cell theory (organelles arise from pre-existing organelles).

Viruses are non-cellular: no plasma membrane, no ribosomes, no metabolism of their own. They are not classified by cell theory.

Archaea are a separate prokaryotic domain with distinct biochemistry (membrane lipids, RNA polymerase). The "three-domain" view (Bacteria, Archaea, Eukarya) replaced the older "five-kingdom" view in the 1990s.

They have no membrane-bound organelles. Ribosomes, nucleoid and cytoskeletal proteins are still present.