In addition to what niky just said, I'd add that some of these structures appear to 'behave' as if they are aware of what they are doing, but that there is a difference between having a purpose and being of aware of having a purpose. The behaviour of everything in the cell is governed by their chemical and physical properties, and the usefulness of any given biomolecule or structure is refined and retained by the process of natural selection. However amazing they may be, it's perfectly feasible to explain how these things came to be the way they are if we take into account the vast length of time involved in their creation. Some chemical reactions - such as electron transfer reactions in photosynthesis - happen on such a fast time scale that these reactions can happen more times in one second than the total number of seconds the average human being will live. In other words, one second on a human time scale is very short, but on the atomic/molecular time scale it can be extremely long (equivalent to a 'human lifetime'). Now couple that with the fact that the Earth is 4 billion years old, and you've got yourself a truly massive timescale over which these things can evolve...