Cell Theory, History, and Function – The cell theory was given by Mathias Jacob Scliden, 1838 and Theodore Schwann, 1839. He said that the body of plants and animals is made up of cells and products of cells.
Rudolf Virchow was the first to state that Omnis Cellulaie Cellula means all cells arise from pre-existing cells, that is, the cell divides, and new cells are generated by the division of pre-exiting cells. originates from.
Modern cell theory
Table of Contents
Rudolf Virchow modified this theory of Schleiden and Schwann and propounded a new cell theory, which is called modern cell theory. according to-
The body of every living being is made up of one or more cells.
Cell is the structural and functional unit of living things.
All cells are basically the same. Contains Cytoplasm, Nucleus and Organelles.
The cell is covered by a thin cell membrane and cell wall. Cell wall is found only in plant cells, not in animal cells.
Chemical compostion and metabolic reactions of all cells are the same. Hence the cell is called the functional unit of living things.
New cells are formed by the division of earlier cells.
Cells contain genetic material which is passed on from one child to another. Hence the cell can be called the unit of heredity.
Exception of Cell Theory
The following are the exceptions to the cell theory:
(I) Virus
Viruses are acellular and contain only nucleic acids (DNA or RNA) and proteins.
(II) Virus particles
Viruses are simply called RNA particles.
(III) Virions
These are inactive carriers of the viral genome.
(IV) Prions
It is the outer covering of the virus-only protein, in which nucleic acids are absent.
(V) Red Blood Cells (RBC)
The nucleus is absent in the blood of mammals. The nucleus is present in the RBC of camel and llama.
(VII) Lymphocytes
Typical genetic material is absent in B and T lymphocytes.
These are called exceptions because of the following reasons –
- They lack cell membranes, protoplasm, cytoplasm, enzymes, other cellular components, etc.
- They do not have the ability to divide. They need a live host cell for their division.
- Generally, either DNA or RNA is present in them. Whereas both nucleic acids are found in every cell.
