Is everything made of the same material?

Mostly, as you mention later in your post, from 'gathering' from the environment. This can be somewhat passive, like what trees do, or can be very active, like what we do when we hunt for a hamburger in the concrete jungle. Mostly, the answer is yes. We, plants and bacteria are all carbon-based lifeforms, meaning we are all made of chemical compounds comprised mostly of carbon, (with significant amounts of nitrogen, oxygen and hydrogen). All life as we know it uses DNA, RNA, fatty lipids, carbohydrates and mostly the same set of amino acids (exceptions exist of course). These nucleic acids (DNA and RNA) and the amino acids of the proteins aren't arranged in the same order, or present in the same amount, and aren't in the same spot within the cell, but mostly they are the same. These variations are, as you have pointed out, controlled by the DNA.This is a good analogy, especially for the eukaryotes (like plants). The boss (DNA) stays in his office (the cell nucleus), and sends his managers (the RNA) to the employees (the rest of the cell) to gather the materials (from the environment). Bacterial are prokaryotes, so their DNA boss actually doesn't have an office, but walks around with the employees.

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Pretty much.I may also note here, that the number is actually quite a bit higher than 20, due to what is called "post-translational modifications". Basically, using the Lego analogy, this is like breaking the Lego blocks to fit them into the construction properly. In much the same way, the amino acid called Proline can get a hydroxy (oxygen plus a hydrogen) group attached to form Hydroxyproline to fit them better into the common protein (that you may have heard of) called 'collagen ' (it's also found in elastin).Sorry for confusing you additionally, but just have to point out that there are many exceptions to 'rules' in biology. Oh, there are certainly useless proteins. For example, as crashfrog said, the proteins have to fold into the right conformation, but over time (or with stress, like high temperatures), they unfold and break. Mutations can also create useless (misfolded) proteins. Organisms of course have evolved to live with this, so they have structures (also proteins) we call 'chaperones' to refold the proteins, and 'proteasomes' to break up those damaged beyond repair, so they can be recycled. Very much so. Of course, there are things that both bacteria and plants need to do, like gain energy, replicate their DNA and divide their cells, so the proteins that do these jobs are very similar in both organisms. Yes, although mutations aren't always the only thing that can lead to evolution, but we'll save that for another topic. Certainly. In fact, much of evolutionary biology has moved away from looking at skeletons and organs, and towards looking at the DNA of species in order to determine the relationship between living species. The fact that both methods gave much the same results is a good evidence for evolution, in my opinion.Edited by Doddy, : formatting of quote boxesEdited by Doddy, : slight spelling error

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This is true. However, in terms of large organism, how much DNA you have to replicate is the last of your concerns (that is, growth speed is not as important). What is actually coded for by the DNA (what you look like and how you function) affects your survival and reproduction much more than taking an additional minute for cell division while you replicate the DNA.However, on the scale of microorganisms, it is very important that you replicate faster than your neighbours, and so you find that single-celled organisms have much less junk DNA, due to the selection acting against it.

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Just to clarify something here: although the organism in the past, the one that absorbed (or was infected by, depending on you point of view)these little bacteria and kept them as mitochondria or chloroplasts, would have looked like a bacteria, modern bacteria do not have these organelles. Only eukaryotes (like us, plants, fungi, amoeba etc) do. Therefore, this means that those bacteria that obtained these organelles must have evolved into the single-celled ancestors of eukaryotes, leaving the bacteria without them to remain as bacteria.As far as your guess goes, you are exactly right. Both mitochondria and chloroplasts replicate seperately to the host cell, and when the cell divides, half (roughly) of the mitochondria/chloroplasts go to each cell.This is important to note for sexually reproducing organism, as sperm/pollen cells do not give their mitochondria to the egg cell (they only give their nucleus). Therefore, while you may have your mother's or your father's genes, you can only have your mother's mitochondria!

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