Life on Earth takes on many different forms. One of the most basic categories of life the nature of the cells that constitute an organism. There are two major types of cells, eukaryotes and prokaryotes. Prokaryotes are bacteria, while every plant and animal is made of cells that are eukaryotic is nature.
Okay, so that’s nice, but what exactly defines a eukaryotic cell? The most important feature of a eukaryotic cell is the membrane bound DNA. The genetic material for the cell is contained in a nucleus. Prokaryotes do not have a nucleus.
There are other significant features of a eukaryotic cell. Most animals have many mitochondria in their cells. These are small organelles that are responsible for making energy that the cell needs to live. Interestingly, a current theory regarding mitochondria is that they were once a totally different organism that was “swallowed” and incorporated in to the metabolic machinery of the cell. Of course, if this happened, it took place hundreds of millions of years ago – not last Tuesday.
Plants are also eukaryotes. Plant cells have many features that differentiate them from animal cells. The cell wall of a plant cell has a hard, rigid structure – not just a simple membrane that is seen in an animal cell. Instead of mitchondria, plants get their energy from chloroplasts. These are highly specialized structures that turn light in to a storable chemical form. Chloroplasts are also what makes a plant leaf green.
In addition to plants and animals, other groups of life that are made of eukaryotic cells are fungi and protists. It’s reasonably safe to say that if it’s not a bacteria or another category called archaea, it’s made of eukaryotic cells.
Eukaryotes are generally more complex organisms compare to prokaryotes. Almost all multi-cellular life is made of eukaryotes. There are some exceptions to this of course.
Eukaryotic cells divide by the process of mitosis. This is a complex set of organizational steps that the cell goes through in order to make two identical cells out of one parent cell. For species that undergo sexual reproduction, sex cells are made by a process called meiosis. The processes of mitosis and meiosis are specific to eukaryotic cells.
Eukaryotic cells are very old. It is estimated that the first eukaryotic cells appeared on Earth between 1.5 and 2 billion years ago. That’s a really, really long time ago. With any luck, they will be around for another two billion years.