All About Biological Sciences

Encompasses the Biological World

HISTORY OF CELL AND CELL THEORY

Cell is known as the basic unit of life. it is the building block of complex multicellular individuals and it can direct all the activities of living species. In multicellular organisms there is a division of labour among cells. Different cells are specialized for different functions. The function of the organism as a whole is the result of the sum of activities and interactions of different cells and of different components of the cell. In animals e.g., muscle cells contract and relax, nerve cells transmit impulses, gland cells secrete hormones, red blood cells carry oxygen and some stomach cells secrete gastric juices. Similarly in plants xylem cells conduct water and mineral salts from soil to the aerial part of the plant. Phloem cells translocate food, sclerenchymatous cells give support to the plants, chlorenchymatous cells carry out photosynthesis, parechymatous cells store surplus food and meristematic cells produce new cells for growth and development of the plant. As they perform different functions they show great variation in shape and size. Despite the structural and functional diversity the plant cells as well as animal’s cells have a common plan of organization. Cells are capable of metabolizing its own nutrients, synthesizing many types of molecules providing its own energy, replicating it-self to produce succeeding generations. The wings of butterfly are a thin sheet of cells, so is the shiny layer of our eyes. The meat we eat is composed of cells and its contents soon become part of our cells. Our eyelashes, fingernails, orange juices, the wood of pencil all are produce by cells.
 The invention of microscope leads to the study of cell. During 16 century there were two main inventions in the Holland, Microscope and Telescope. The first microscope was invented by Zacharias Jansen. It was a simply tube with lenses at each end and its magnification ranged from 3X to 9X. In the history of biology ancient Greeks were the first who organized the data of natural world. Aristotle presented the idea that all animals and plants are somehow related. Cell was first described by a British scientist Robert Hooke in 1665. The first living cells were observed a few later by a Dutch naturalist Antonie van Leeuwenhook. In 1809, Jean Baptist de-Lamarck proposed that “no body can have life if its parts are not cellular tissues are not formed by cellular tissues”. In 1833 a British botanist Robert Brown discovered nucleus in the cell. In 1838-39 working independently by two scientist came out a theory called cell theory, a German botanist Matthias Schleiden and a German zoologist Theodor Schwann proposed cell theory. The cell theory is one of the most fundamental generalizations in Biology. It has wide ranging effect in all fields of biological sciences. After the cell theory was presented many details of cell were studied as a result of which the cell theory was extended.
 In 1885 Rudolf Virchow a German physician extended cell theory. He proposed that all living cells arise from pre-existing cells. In 1862 Louis Pasteur provided experimental proof of this idea by demonstrating that microorganisms (bacteria) could be formed only from existing bacteria. In 1880 August Weismann said “all presently living cells have a common origin because they have basic similarities in structure and molecules etc.
The cell consists of 3 basic parts viz nucleus, the fluid (cytoplasm) surrounding the nucleus and the outer thin covering or membrane (plasma membrane). The cell wall is an additional structure present in plant cells.

The cells have ability to divide as it may be smallest as bacteria (0.3µm) or largest as human (which is 4 lack times larger than bacteria cell). Cells division is a mean of reproduction of in unicellular organisms while it is a way of growth and maintenance in multicellular organisms.
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