Organisms which do not possess a well formed nucleus are prokaryotes such as the bacteria. All others possess a well defined nucleus, covered by a nuclear membrane. They are eukaryotes.
(eu means true and karyon means nucleus)
- Nucleus distinct, with well formed nuclear membrane.
- Double-membraned cell organelles (Chloroplasts, mitochondria, nucleus) and single-membraned (Golgi apparatus, lysosomes, vacuole, endoplasm reticulum) are present
- Ribosomes - 80 S
- Distinct compartments in the cell - the cytoplasm and the nucleus
- Depending upon the species number of chromosomes per nucleus varies from two to many.
- Each chromosome is linear with its two ends free.
- Each chromosome has one linear double-stranded DNA complexed with histones.
- Each chromosome has one centromere that divides a chromosome into two arms. However, if the centromere is terminal, the chromosome would have only one arm.
Pro means early or primitive
- Nucleus not distinct, it is in the form of a nuclear zone nucleoid. Nuclear membrane is absent.
- Single-membraned cell bodies like mesosomes present. Endoplasmic reticulum, plastids, nitochondria microbodies like lysosomes, and Golgi body absent.
- Ribosomes - 70 S
- No compartments
- There is only one chromosome per cell
- The chromosome is circular and remain attached to cell membrane at one point
- The chromosome has single double-strande circular DNA molecule and is not associate with histones.
- The chromosome lacks a centromere.
Plant Cell and Animal Cell
- Cellulose cell wall present external to cell membrane.
- Vacuoles are usually large.
- Plastids present.
- Golgi body present in the form of units known as dictyosomes.
- Centriole absent.
- No cell wall, outermost structure is cell membrane or plasma membrane.
- Generally vacuoles are absent and if present, are usually small.
- Plastids absent.
- Golgi body well developed having two cisternae.
- Centriole present.