The oldest known multicellular eukaryote is believed to be Grypania spiralis, whose fossil dates back to about 2.1 billion years. It can be found as thin films of carbon in Negaunee iron formation at the Empire Mine near Ishpeming, Michigan.
Cells have been broadly classified as: prokaryotic cells and eukaryotic cells. These terms come from the Greek word "karyon" which means "nucleus". This nucleus is considered as the brain of the cell, which directs it properly. "Pro" means "before" and "eu" means "true".
Thus, prokaryotic cells do not have a nucleus and are supposed to be primitive in nature, while the eukaryotic cells have evolved from the former ones, and show the presence of a nucleus.
Difference Between Prokaryotic and Eukaryotic Cells
|Cell Characteristics||Prokaryotic Cells||Eukaryotic Cells|
|Featured in organisms||Domain Bacteria and Archae||plants, animals, fungi, algae, protozoans|
|Origin||3.5 billion years ago||1.5 billion years ago|
|Size of the cell||0.5 micrometer in diameter or may be less||5 micrometer in diameter or more|
|Nucleus-brain of the cell||Absent||Present|
|Nuclear membrane or Nucleolus||Absent||Nucleus enclosed within the Nuclear membrane|
|The genetic material-Deoxyribonucleic acid(DNA)||DNA is freely floating and circular, not bound by the nuclear membrane, popularly called Nucleoid||DNA is linear and bound by nuclear membrane|
|Plasma Membrane or Cytoplasmic Membrane or Outer Membrane (phospholipid bilayer)||Lacks sterols||Consists of sterols and carbohydrates|
|Chromosomes||Contain Histone-like proteins||Contain Histone proteins|
|Reproduction||By binary fission||Mitotic and meioitic division seen|
|Zygote||Is partially diploid (merozygotic)||Is diploid|
|Cell wall||Contains peptidoglycan||Animal cells lack cell wall. Others have either cellulose or chitin|
|Capsules-slimy coverings||Present in bacterial cells||Absent|
|Ribosomes||70S type||80S type. Though mitochondria and plastids have 70S type|
|Chloroplast||Absent||Present in plants|
|Gas vacuoles||May be present||Present|
|Mesosomes||May be present||Absent|
|Endocytosis and Exocytosis||Absent||Present|
|Locomotary organ||Flagella present which are made up of less number of fibrils and do not show (9+2) microtubule arrangement||Flagella and pili present which have complex mechanisms and show microtubule arrangement (9+2)|
|Energy yielding mechanisms (Electron transport chain)||Occurs in cytoplasmic membrane||Occurs in mitochondrial membrane by glycolysis cycle|
As evident till now, all living beings are made up of cells and cell products, consisting of a number of cell organelles, which help in carrying out various life processes. A matter of debate between prokaryotic and eukaryotic cells is mitochondria - the energy-yielding organelle, which is supposed to be independent. They have their own genetic material - the DNA and hence, are capable of division. They have a symbiotic sort of relationship with the cell in which they reside. Thus, it might be obvious that they have originated from a single independent prokaryotic unit, since they are similar to them, in the sense that they have an unbound circular DNA. But the surprising thing is that the prokaryotic units lack mitochondria. Does this mean that it is a living organism residing inside another cell, or is it just an independent organ? If you are aware of all the scientific terms used, it will be easy to grasp.