EMERGENCE AND IMPLICATION OF CELL THEORY

EMERGENCE AND IMPLICATION OF CELL THEORY

The cell can be defined as structural and functional unit of life. It is the smallest unit of the body. It can perform all the activities of life. The cells are building block of complete multi cellular organisms. Following scientists played their role in the formulation of the cell theory:

1.  Robert Hooke

He discovered cell in 1665. His work on cell was published in "Micrographia". He prepared a thin section  of cork. Cork is made up of dead plant material. Hooke studied this section under his self made compound microscope.  He observed that the cork was composed of minute honey comb like compartments. He called them cells. He described cell as an empty space. They are covered by thick wall.  

2.  Lorenz Oken: (1805)

He was a German scientist. He believed that all the organisms originate from vesicles. So these organisms consist of vesicles or cells.

3.  Jean Baptist de-Lamarck: (1809)

He also believed that a body cannot have life without cellular tissues. All its parts are formed by cellular tissues.

4.  Robert Brown

He discovered nucleus in cell in 1831. It changed the Hooke's idea that the cells have empty spaces. He proved that the cell is not an empty space.

5.  Theodor Schwann and Schleiden

Schwann was a German zoologist (1839) and Schleiden was a German botanist (1838). Both these scientist were working independently. They formulated Cell Theory. They find that cell consists of 3 basic parts: 

➤ Nucleus, present in middle.

➤ Cytoplasm, it surrounds the nucleus.

➤ Plasma membrane, it forms outer thin covering.

Cell wall is an additional structure. It is present only in plants. They observed plant and animal material and formulated following cell theory: The cell theory states, "All the living organisms are composed of cells and cell products". It is a most gernalized theory in biology. This theory has great effects on the biological research. Many details of the cell were studied. The cell theory was extended on the basis of these studies.

6.  Rudolph Virchow: (1855)

He was German physician. He made a hypothesis that the new cells are formed only by the division of previously living cells. In Virchow's words, " omnis cellula e cellula. " At that time there were two

ideas about the origin of life.

➤ Abiogenesis: It states that the living things arise from the non- living things. It was most popular idea of that time. 

➤ Biogenesis: It states that the living things arise only from the living things. Virchow's hypothesis supported the idea of biogenesis and opposed the idea of Abiogenesis. On the basis of Virchow's hypothesis a new working definition of the Cell theory was formed:

It states that "Living things are chemical organizations. These are composed of cells and capable of reproducing themselves. "

 7.  Louis Pasteur: (1862)

He was one of the greatest scientists of his time. He supported the Virchow's hypothesis with experiments. He proved that microorganisms (bacteria) could be formed from existing microorganisms.

8. August Weismann: (1880)

He said, "All presently living cells have a common origin because they have arts basic similarities in structures and functions. " There are fundamental similarities in the chemical composition, metabolic activities, and structures of the organisms. Some small differences may be present.

Therefore, the cells are basically similar but extraordinarily versatile. This cell is the structural and functional unit of the living organisms. So cell theory is a very important unifying concept.

Salient  Features of Cell Theory
Cell theory has following salient (important) features:
1. All organisms are composed of one or more cells.
2. All cells arise from pre-existing cells.
3. Cell is the basic structural and functional unit of all the organisms.
Cell as unit of structure and function
A cell is unit of structure and function in lwing organisms. There is a division of labour among cells in the multicellular organisms. Different cells are specialized for different functions. Different cells and different components of the cells perform different activities. It results in the functioning of the whole organism. These cells perform different functions. So they show great variations in shapes and structures. Despite these variations, the plant cells and animal cells have a common plan of organization.

For example
Animals

➤ Muscle cells contract and relax.

➤ Nerve cells transport impulses

➤ Gland cells secrete hormones.

➤ Red blood cells carry oxygen.

➤ Some stomach cells secrete gastric juice.

Plants

➤ Xylem cells conduct water and mineral salts from soil to the plant body.

➤ Phloem cells translocate food.

➤ Sclerenchymatous cells give support to the plant.

➤ Chlorenchymatous cells carry out photosynthesis.

➤ Parenchymatous cells store surplus food.

➤ Meristematic cells produce new cells for growth and development.