Complex Organisms Developed
03/12/2010 § 1 Comment
In class, we began discussing how complex organisms developed from tiny, single celled and very simple prokaryotes (typically types of bacteria) to the forms of organisms we have today. Prokaryotes merged to make the complex cells we see today. They did what is called endosymbiosis to form something like a super cell.
The prokaryotes that started this endosymbiosis were bacteria—bacteria that still exist today. Prokaryotes (including bacteria) still make up half of the bio mass on earth today, and apparently we as humans are covered in them day in and day out; it doesn’t matter how many times we take a shower.
Some bacteria, however, were responsible for making the first slightly more complex cells that began the evolution of eukaryotes. Some bacteria back then were photosynthetic and aquatic, meaning they could live in water and make glucose, or at least food, from the energy of the sunlight. As we know, this ability to make food out of sunlight is photosynthesis. The bacterium that could do this was cyanobacteria which is important in making the first eukaryotes of this world.
Another important bacterium that played a part in merging to be a eukaryote is the eubacteria. A eubacterium is able to break down foods, like sugar, for itself and eventually became an organelle for the first eukaryote.
Finally, there was archaebacteria. Almost literally, archae- is translated loosely to “ancient” or more so to “primitive” (according to my trusty online dictionary) in latin which means: archaebacteria is one of the (or the oldest) bacterium. What came as a small surprise to the class was discovering that humans are actually more closely related to archaebacteria than they are to any other type of bacteria… not that we’d want to be related to bacteria. But we are. Whether we like it or not. Some closely related characteristics between humans and archaebacteria are the presence of DNA and introns, the lack of peptidoglycan (amino acids and sugar) in our cell walls, the presence of unique lipids in our cell membranes (phospholipid bilayers, making us flashback all the way to August/September’s biochemistry unit) and an archaebacterium’s ribosomes are similar to eukaryotic ribosomes. The archaebacteria played possibly one of the most important roles in the formation of the first eukaryote.
A eubacterium began eating at a host bacteria which just happened to be archaebacteria, a larger and just slightly more complex cell. The archaebacteria allowed itself to be eaten at and ingested the eubacteria but did not digest it. The eubacteria began living inside its host cell and eventually, the two transform to adapt to their new situation. They, together, become a eukaryote. The archaebacteria becomes the eukaryote itself and inside it, the eubacteria becomes the first mitochondrion. This is why mitochondria have such similar characteristics to eubacteria: they evolved from eubacteria. The same thing happened to chloroplasts (photosynthetic organelles). Instead though, they evolved from cyanobacteria (photosynthetic bacteria).
Now, since there are a variety of different ways to be multicellular, organisms’ diversity comes with the way they divide. Since all cells stick together every time they divide and express some DNA (but not all of it), new species began.
Finally, in the last 5 or so minutes of class, we heard the words “mass extinction” which is basically an extended extinction. Since extinction is when a single species dies out, a mass extinction is then when many species die out. It’s a terrible thing. There are five mass extinctions in the history of Earth so far, but I can really only remember them with the letters ODPTC which make up ‘Oh Dear Pretty Terrible C———” but I’m sure the lecture notes will help me force myself to remember the real periods’ names.
As for the essay question, now I know that it is: How do things change? and it turns out my predictions of the essay question was right. It very much has everything to do with how living things and how organisms evolved into the complex structures they are today.