A plant cell is protected by the presence of a cell wall while animals have a semi-permeable cell wall. Schwann was a German zoologist who one year after Schlieden said that animals were composed of cells. Virchow was a German physician who said that all cells come from pre-existing cells. All living things are made up of one or more cells. Cells are the basic living units within organism and the chemical reactions of life take place within cells.
All cells arise from pre-existing cells.
All organisms obey the laws of chemistry and physics. Until the turn of the century there were scientists who defined themselves as vitalists. They believed that living systems contained vital spirits which enabled them to perform certain activities and these specific activities could not be reproduced outside of a living system. This is no longer believed. The first organic substance produced in the lab was urea.