Prokaryotic and Eukaryotic cells
Cells are the fundamental units of life, forming the basic structural and functional components of all living organisms.
They exist in two primary types: prokaryotic and eukaryotic, each with distinct characteristics.
Prokaryotic cells, such as bacteria, are simpler and smaller, lacking membrane-bound organelles and a nucleus, with their DNA instead being located in a region called the nucleoid.
Eukaryotic cells, found in more complex organisms such as plants, animals and fungi, contain membrane-bound organelles like the nucleus, mitochondria and chloroplasts.
| Feature | Prokaryotic Cells | Eukaryotic Cells |
| Nucleus | Absent. DNA is present but not enclosed by a membrane. | Present. DNA is contained within a membrane-bound nucleus. |
| Membrane-bound organelles | Absent | Present |
| Size | Generally smaller, ranging from 0.1 to 5.0µm in diameter. | Generally larger, ranging from 10 to 100 µm in diameter. |
| Genetic material | DNA is typically a single, circular molecule. | DNA is organised into multiple linear chromosomes located inside the nucleus. |
| Ribosomes | Smaller (70S). | Larger (80S). |
| Cell division | Typically reproduce through binary fission, a form of asexual reproduction. | Reproduce through mitosis (for somatic cells) or meiosis (for gametes). |
| Complexity and specialisation | Generally less complex and less specialised compared to eukaryotic cells. | Generally more complex and more specialised, with a wide range of cell types performing specific functions |
| Evolutionary origin and relationship | Considered to be more ancient, representing the earliest forms of life on Earth. | Evolved later and are more complex, likely arising through a process of endosymbiosis where membrane-bound organelles have evolved from engulfed prokaryotic cells. |
| Example organisms | Bacteria and archaea. | Plants, animals, fungi, protists and algae. |
The endosymbiotic theory suggests that eukaryotic cells evolved when early prokaryotic cells engulfed other prokaryotes, which then became symbiotic organelles. This theory explains the presence of DNA in organelles like mitochondria and chloroplasts.
