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In 19th century, the compound microscope was highly advanced and biologists observed things just a micrometer apart. After this, a series of discoveries started, which provided basic information for cell theory.
1. In 1831 - 33, Robert Brown discovered nucleus in cells of plants.
2. In 1838, a German botanist Mathias Scheiden observed that all plants were made up of cells.
3. In 1839, Theoclor Schwann observed that the bodies of of animals were made up of cells which were similar to plant cells.
4. Thus, Schleiden and Schwann formulated the "Cell Theory". According to this, all organisms are made up of cells.
5. In 1840, J. Purkinji gave the name "Protoplasm" to the things found inside the cells. At that time, cell was considered as a bag of thick dense substance containing a nucleus.
Later on, resolving power and quality of microscopes were highly improved. Section cutting of tissues and cells and their staining became easier and better. It revealed that cell was not a simple mass of granular substance; instead it contained many sub cellular bodies called "Organelles". Each organelle has a definite job in the cell.
6. Human is made up of about 60 trillion cells. From Amoeba and unicellular algae to whales and tallest red wood trees, all' are made up of similar basic units called cell.s All animals and plants are thus made up of cells and cell products.
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