Most people today appreciate that we are made of billions of cells. However, this was not always the case. Cells are too small to be seen with the naked eye, so it was not until microscopes were available that people could see that animals and plants were made of cells. Scientists also observed single-celled organisms for the first time. As microscopes improved, biologists were able to see the even smaller structures inside cells and sophisticated biochemical techniques enabled them to work out what each part of the cell actually did.

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