NCERT Solutions for Class 11 Biology Historical Background and Discovery of Cell
Biology notes for Class 11 – Unit 2 – Definition of Cell Biology
The biological science that deals with the study of structure, function, molecular organization, growth, reproduction and genetics of the cells, is called Cell Biology or Cytology.
Historical Background and Discovery of Cell
- Ancient Greek philosophers such as Aristotle (384-322 B.C.) and Paracelsus concluded that complicated structure of animals and plants are constituted of few elements which are repeated in them. These were the macroscopic structures of an organism such as roots, leaves, and flowers in case of plants, while organs in case of animals.
- After the invention of magnifying lenses, in 1558, a Swiss biologist, Conrad Gesner (1516-1565) studied the structure of a group of protists called foraminifera.
- With the invention of the compound microscope, in 1590 by Francis Janssen and Zacharias Janssen, there was further growth in the studies in cell biology.
- The Italian microanatomist Marcello Malpighi (1628- 1694) examined thin slices of animal tissues from organs such as brain, kidney, spleen, lungs, and he also studied plant tissues and suggested that they were composed of structural units, and he called these units as “utricles”.
- Robert Hooke (1635-1703), an English microscopist, coined the term Cell (in Latin cell means – hollow space).
- Robert Hooke examined a thin slice cut from a piece of dried cork under a compound microscope. In 1665, he published the collection of essays under the title, Microphagia, one essay described cork as a honeycomb of chambers or cells. Hooke thought of the cells he observed something similar to veins and arteries of animals- they were filled with “juices” in living plants.
- Anton van Leeuwenhoek, described in 1675, microscopic organisms in rainwater collected from tubes inserted into the soil during rainfall. His sketches included numerous bacteria, protozoa, rotifers, and Hydra. Leeuwenhoek was the first to describe the sperm cells of humans, dogs, rabbits, frogs, fish, and He was also the first to observe the movement of blood cells of mammals, birds, amphibians, and fish, he noted that those of fish and amphibians were oval in shape and contained a central body (now termed as the nucleus); while those of humans and other mammals were round. He also observed the striated muscles.
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- An English plant micro anatomist Nehemiah Grew (1641-1721) published accounts of the microscopic examination of sections through the flowers, roots, and stems of plants and clearly indicated that he recognized the cellular nature of plant tissues.
- In 1807, Mirbel stated that all plant tissues were composed of cells. French biologist, Rene Dutrochet, concluded in 1824, that all animal and plant tissues were “aggregates of globular cells”.
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- Robert Brown (1773- 1858) discovered nucleus in the center of all cells. He established that the nucleus was the fundamental and constant component of the cells.
- In 1838, a German botanist Mathias Jacob Schleiden (1804-1881) put forth the idea that cells were the units of structure in the plants. In 1839, his co-worker, a German Zoologist, Theodor Schwann applied Schleiden’s thesis to the animals. Both of them postulated that the cell is the basic unit of structure and function in all life forms. This simple, basic and biological generalization is known as Cell Theory or Cell Doctrine.
- In later years the cell theory was extended and refined further. Nageli(1817-1891) showed in 1864 that plant cells arise from the pre-existing cells. In 1855, a German pathologist Rudolf Virchow (1821-1902) confirmed Nageli’s principle of the cellular basis of life’s continuity. His statement was that the cells arise only from the pre-existing cells, thus he established the significance of cell division in the reproduction of organisms.
- In 1858, Virchow published his classical textbook Cellular Pathology and in it, he correctly asserted that as functional units of life, the cells were the primary sites of diseases and cancer.
- Later, in 1865, Louis Pasteur in France gave experimental evidence to support Virchow’s extension of the cell theory.
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