Statement of Cell Theory

Statement of Cell Theory:

The cell theory states that __ 

(i) all living things are composed of minute units, the cells, which are the smallest entities that can be called " living"; 

(ii) a cell is a mass of protoplasm containing a nucleus and bounded by a cell membrane, and in many cases by a cell wall also; 

(iii) all cells are basically alike in structure and metabolic activities;

(iv) the function of an organism as a whole is the result of the activities and interactions of the constituent cells.

Like the theory of evolution, the cell theory is surely one of the great unifying principles of biology. Although the cell theory is substantially correct, it does not apply to all organisms. 

* Fontana had seen nucleus and nucleus in 1781,but Brown was the first to name the nucleus  and to propose that it occurs in all cells.


Cell principle is modified  form of cell theory.  Rudolf Virchow ( 1858) in his Cellular Pathology,  expressed his opinions that Omnis Cellula e cellula i..e., the cells have come from pre_ existing ones.

The principle is the modified or modern form of the cell theory. 

Need for Modification in Cell Theory:

Schwann ( 1810_ 1882) held that cells could arise spontaneously. A German physiologist Rudolph Virchow ( 1821_ 1902) found in 1858 that all living cells arise from the preexisting cells omnis cellular  e cellular.This Conclusion suggested a continuous line of cell generations form the very beginning of life.This is called theory of cell lineage.This theory, points out to the evolutionary implication that all cells, and hence all organisms, have a common ancestry . It also made the cell a vehicle for the transmission of hereditary traits from one generation to the next.Haeckel,in 1866, announced that the nucleus stored and transmits hereditary information. 

Better observational instruments and study techniques in the twentieth century have revealed many details about the cell structure and function. This necessitated modification in the cell theory. In the modified form, the cell theory applies almost fully and universally to life, and has, therefore, been given the status of a cell Principle, or cell doctrine.It is also referred to as the  modern cell theory.

Statement of Cell principle:

The cell principle states that ___ 

1. Life exists only in cells.

2. Living objects are composed of cells and cell products, or are multinucleate mass of protoplasm, or are like a single free cell.

3. A cell is a small mass of protoplasm usually containing a nucleus or nuclear and some other organelles, and is bounded by a cell membrane. A cell organelle does not survive alone.

4. Cell is also a unit of function, reproduction, heredity and disease, besides being a unit of structure. 

5. Cells always arise from the preexisting living cells by division. They never arise de novotny. The new cells are like the parent cell in all respects. 

6. All cells existing to _ day can trace their ancestry back to the original cells of ancient time.This also holds good for the cell organelles called chromosomes

7. All Cells have fundamental similarity in physical structure (Organelles), chemical composition and basic metabolic reactions. 

8. Cells maintain homeostasis to remain alive.

9.Functions of an organism as a whole are the sums of the activities and interactions of its constituent cell units. An organism cannot show a function which is absent in its cells.

10. A Cell, through an integral part of an organism, can act ( grow, divide and die) independently of the other cells around it.

11. Each cell is capable of regulating its vital processes. 

12. Genetic information is stored and expressed within the cells.

13. Life passes from one generation to another of the organisms in the form of cells, called gametes. 

14. Cells sometimes assume form which no longer have all the characteristics of cells.

15. Cells may die and still remain functional such as horny cells in animals and xylem vessels in plants.

16. Structure and working of a cell is controlled by DNA.

17. All cells have a full genetic information coded in their DNA, but each type uses only a part of information which is needed for its specialized structure and function. 

A, thus the smallest organization of matter that is capable of all the processes collectively referred to as " life".

Cell Theory Versus Cell Principle. 

The cell principle is better than cell theory  as __ 

1. It applies almost to all the living things: plants animals and microorganisms. 

2. It incorporates nearly all the modern finding about a cell.

Important  features of cell principle are:

1): All the living  organisms are made up of cells.

2): Cells never appear  de novo i.e., they appear  only from the pre_ existing ones.

3) Cells are responsible  for all the metabolic activities  within living  organisms. 

4): Cells are the basic and smallest units of life. 

5): Each cell is capable of maintaining its vitality independently. 

6): A cell is a small mass of protoplasm, containing  nucleus or nuclear material, with some organelles and is bounded by plasma membrane. 


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