All living cells can be classified as either prokaryotic or eukaryotic. Bacteria are prokaryotic, while fungi, protozoa, and other organisms are eukaryotic.
Eukaryotic cells contain a nucleus with a nuclear membrane enclosing multiple chromosomes, while prokaryotic cells have a single chromosome (nucleoid) that is not enclosed in a nuclear membrane. Another major difference between bacterial DNA and eukaryotic DNA is that bacterial DNA has no introns, whereas eukaryotic DNA does.
A key genetic difference between prokaryotes and eukaryotes is that eukaryotes typically contain two copies of each gene and are thus genetically diploid.
Eukaryotic cells also possess a variety of subcellular organelles with specialized functions, such as mitochondria (sites of aerobic respiration) and chloroplasts (sites of photosynthesis in green plants).
Prokaryotic and eukaryotic cells differ substantially in many other characteristics, some of which are tabulated here:
| Features | Prokaryotic cells | Eukaryotic cells |
| Size | 1-2 by 1-4 micrometer or less | Greater than 5 micrometers in width or diameter |
| Genetic system | ||
| Location | Nucleoid, chromatin body or nuclear material | Nucleus, mitochondria, chloroplasts |
| Nuclear membrane | Absent | Present |
| Chromosome | Single, closed, circular double-stranded DNA. | Multiple, linear chromosomes. |
| Histones | Chromosome does not contain histones. | Chromosomes have histones. |
| Sexuality | Zygote nature is merozygotic (partial diploid) | Zygote is diploid |
| Cytoplasmic nature and Structures | ||
| Cytoplasmic streaming | Absent | Present |
| Pinocytosis | Absent | Present |
| Gas vacuoles | Can be present | Absent |
| Mesosome | Present | Absent |
| Ribosomes | 70S, distributed in the cytoplasm. | 80S arrayed on membranes as in endoplasmic reticulum; 70S in mitochondria and chloroplasts |
| Mitochondria | Absent | Present |
| Chloroplasts | Absent | May be present |
| Golgi structures | Absent | Present |
| Endoplasmic reticulum | Absent | Present |
| Membrane-bound (true) vacuoles | Absent | Present |
| Outer Cell Structure | ||
| Cytoplasmic membranes | Generally do not contain sterols; contain part of respiratory and, in some, the photosynthetic machinery | Sterols present; do not carry out respiration and photosynthesis |
| Cell Wall | Peptidoglycan (murein or mucopeptide) as component | Absence of peptidoglycan |
| Locomotor organelles | Simple fibril (flagella) | Multifibrilled with “9+2” microtubules |
| Pseudopodia | Absent | Present in some |
| Metabolic mechanisms | Wide variety, particularly that of anaerobic energy-yielding reactions; some fix nitrogen gas; some accumulate poly-β-hydroxybutyrate as reserve material | Glycolysis is a pathway for anaerobic energy-yielding mechanism |
| DNA base ratios as moles % of guanine + cytosine (G+C%) | 28 to 73 | About 40 |
| Examples | Bacteria, blue-green algae. | Algae, fungi, protozoa, plants, and animals. |
