Types of Cells

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.

Eukaryotic Cell

(eu means true and karyon means nucleus)

1. Nucleus distinct, with well formed nuclear membrane.
2. Double-membraned cell organelles (Chloroplasts, mitochondria, nucleus) and single-membraned (Golgi apparatus, lysosomes, vacuole, endoplasm reticulum) are present
3. Ribosomes - 80 S
4. Distinct compartments in the cell - the cytoplasm and the nucleus
5. Depending upon the species number of chromosomes per nucleus varies from two to many.
6. Each chromosome is linear with its two ends free.
7. Each chromosome has one linear double-stranded DNA complexed with histones.
8. 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.

Prokaryotic Cell

Pro means early or primitive

1. Nucleus not distinct, it is in the form of a nuclear zone nucleoid. Nuclear membrane is absent.
2. Single-membraned cell bodies like mesosomes present. Endoplasmic reticulum, plastids, nitochondria microbodies like lysosomes, and Golgi body absent.
3. Ribosomes - 70 S
4. No compartments
5. There is only one chromosome per cell
6. The chromosome is circular and remain attached to cell membrane at one point
7. The chromosome has single double-strande circular DNA molecule and is not associate with histones.
8. The chromosome lacks a centromere.

Plant Cell and Animal Cell

Plant Cell

1. Cellulose cell wall present external to cell membrane.
2. Vacuoles are usually large.
3. Plastids present.
4. Golgi body present in the form of units known as dictyosomes.
5. Centriole absent.

Animal Cell

1. No cell wall, outermost structure is cell membrane or plasma membrane.
2. Generally vacuoles are absent and if present, are usually small.
3. Plastids absent.
4. Golgi body well developed having two cisternae.
5. Centriole present.