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In some of their chemistry, Archaea resemble more advanced cells which we will meet later (eukaryotes). But there is another domain of simple, single-celled organisms which resemble them in size and shape, the Bacteria.
It seems that early cells divided into these two domains, and while the Archaea remain fairly specialized, the Bacteria, have diversified and now form the largest domain of prokaryotes.
The oldest fossil Bacteria found so far are in rocks from western Australia dating from the Archaean 3.5 billion years old.
These are the simplest cells we find on Earth today, called bacteria (sometimes called germs). Note that one of these is called a bacterium.
The delicate of early life had to be surrounded by a strong wall, to stop the membrane breaking. was now packaged into little boxes called cells. Some cells today still have a cell wall.
have cell walls made of peptidoglycan, a large polymer of and .
Plants also have cell walls.
If a soccer ball were inflated to the size of the Earth () then the bacterial would be a rigid open scaffold-like structure 1 meter thick with many holes where small molecules can get in and out. Remember that inside the cell wall there is a thin, flexible cell membrane.
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