Answer:
1839
Step-by-step explanation:
Cell theory could be stated as "all organism are made u of organizational unit known as a cell". One of other notable theory about cell is that of Darwin Evolution theory.
Schwann and Schleiden were able to come up with their theory after seen the similarities that exist between the plant cell and animal tissue in the year 1839, which they later carry out some analysis in the Laboratory and comes up with their cell theory which they stated as the building block of life that made up of all living things.