Question

How long did it take for scientists to develop the cell theory?

Answer 1

Cell theory in biology is the now widely accepted historical scientific theory that living organisms consist of cells, that they are the fundamental structural/organizational unit of all organisms, and that all cells originate from pre-existing cells.

Complete answer:
There was no understanding of cells until 330+ years ago. The cells were too tiny to see. But an entirely new universe was discovered with the advent of the microscope, where very large objects, such as humans, are actually made up of billions of tiny individual parts called cells.

Date	Event
1665	Cells first observedRobert Hooke, an English scientist, found a honeycomb-like structure in a cork cut using a primitive compound microscope. He saw only the cell walls as dead tissue. For these individual compartments he saw, he coined the word "cell"
1670	First living cells seenAnton van Leeuwenhoek, a Dutch biologist, looks at the pond water with a microscope for which he made lenses.
1683	Miniature animalsAnton van Leeuwenhoek made some further observations at the microscopic level, finally publishing a letter to the Royal Society in which he included extensive sketches of what he had found. Among these, the first protozoa and bacteria were discovered.
1833	The middle of the cell is seenRobert Brown, an English botanist, discovered the nucleus of the plant cells.
1838	Basic blocks of buildingMatthias Jakob Schleiden, a German botanist, argues that all plant tissues should be made up of cells and that the cells should be the essential building blocks of all plants. This assertion was the first general statement about the cells.
1839	Cells TheoryTheodor Schwann, a German botanist, came to the conclusion that not only plants, but also animal tissue is made up of cells. This ended discussions that the structure of plants and animals was radically different. It also consolidated and organised the previous statement on cells into one principle which states: 1-Cells are organisms and all organisms consist of one or more cells 2-Cell is the basic unit of structure for all organisms.
1840	Where life comes fromAlbrecht von Roelliker learns that sperm and eggs are both cells.
1845	Basic Life UnitCarl Heinrich Braun is reworking cell theory, calling cells the fundamental unit of life.
1855	Part 3 of the cell theory has been addedRudolf Virchow, a German physiologist/physicist/pathologist, applied the third part to cell theory. The original is Greek, and it says Omnis cellula e cellula. This translates as all cells only grow from existing cells. Virchow was also the first to say that diseased cells come from healthy cells.

Note: New Theory Of Cells
1)All known living things are made of cells.
2)The cell is the structural and functional unit of all living beings.
3)Both cells come by division from pre-existing cells. During cell division, cells hold genetic information that is transferred from cell to cell.
4)In chemical composition, all cells are essentially the same.
5)Within cells, all the energy transfer (metabolism & biochemistry) of life occurs.