How long ago did people know that the bodies of living things are made of cells? Explain why this was not known before.

The first person to know that all organisms are composed of the smallest elements – cells, was Robert Hooke. Studying a cut of a tree under a special magnifying device, which was improved by him, this English scientist discovered that the cut is a huge number of tiny honeycombs, which he later called cells. This discovery took place in the second half of the seventeenth century and this was the beginning of a new science – cytology. Previously, this was impossible because there were no powerful microscopes to see cells.