How do organs complex organisms organized?

Answer 1

There are a number of ways in which organims can become more complex over generations, but the easiest method to convey and understand is through symbiosis..

On the single-cell level, there are two basic divisions known as "domains". One being called, "prokaryotes", and the other being "Eukaryotes. Eukaryotes are distinctively more complex due to the fact that they contain organelles and a nucleus containing it's DNA, whereas, prokaryotes simply have dna floating throughout their cell. It is thought that eukaryotes developed from multiple prokaryotes living symbiotically until, eventually, some prokaryotes began to live their entire lives inside other ones. This explains why mitochondria inside your own cells have their own DNA separate from the DNA in the nucleus (Apparently, at one time, they were independent organisms which found an advantage in the protection provided by your cells membrane while your cells found an advantage in the abundance of energy that the mitochondria provided).

Multicellular life appears to have developed from multiple eukaryotes grouping together colonially (as in the case of chlorella vulgaris, which became multicellular in a predatory environment under laboratory conditions). As later generations become more reliant on one-another, certain cells become better adapted to specific tasks involved in promoting the overall fitness of the body of cells. This results, eventually, in some cells becoming specialized tissues that, in turn combine to form the specialized structures we call "organs".

The perfect example of all of this is your own body which is literally a walking fortress of creatures that have become symbiotic with all of your specialized tissues which, themselves, have diversified into separate structures over a long series of generations. There are actually more bacteria living in your body performing specialized tasks than there are human cells. If those bacteria weren't there you couldn't digest food or process nutrients. Similarly, those prokariotic bacteria couldn't live without your body.

I'm sure there's someone else who would be glad to explain the genetics, mutations, and the selection mechanisms behind all of the above, but my intent was to keep it as simple as I could.

Answer 2

Plants obtain their energy from the Sun; animals obtain their energy from plants (perhaps indirectly, by eating other animals that eat plants); some living beings can obtain energy from chemical reactions, using substances that are available to them.