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Subject: Zoology

Cell Biology definition and History “Life is manifested only through the functioning of intact cells,,never in their absence”..Diversity in the conformational organization of the bio-molecules results in the living world with different types of cellular organisms.

Cell is the basic unit of all living organism.It is the smallest part of the body of an organism which is capable of independent existence and performing the essential functions of life.

• The word Cell comes from the Latin word “Cella” means “Hollow cavity” • Cell can be defined as the fundamental structural and functional unit of all living beings. • Study of cell structure is called Cytology • Study of life at cellular level is called Cell Biology. • Cell Biology deals with all aspects of cell including structure and metabolism.

History of Cell Biology

The invention of microscope by Hans and Zacharias Janssen in 1590 opened up a smaller world showing what living forms were composed of.

• Robert Hooke first identified the compartment like structures in the cork . • Hooke (1665) observed a thin slice of cork under microscope and observed rectangular spaces which looked like small rooms inhabited by monks, hence named them as cells.

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Fig.1.Robert Hooke Fig.2.Cork cells

• His observations were published in a book called Micrographia. • However, what Hooke actually saw under the microscope was the cell walls of dead cells., Hooke did not know their real structure or function. • The first man to witness a live cell under a microscope was Antony van Leeuwenhoek (1674). • He observed many microscopic organisms like protozoans, bacteria, algae and sperms and described them as animalcules. • After the discovery of Nucleus in the year 1831 by Robert Brown and

description of cell contents as protoplasm by Purkinje in 1837 the concept of cell became as a mass of protoplasm, limited in a cell membrane and possessing a central nucleus.

• In the year (1838), Matthias Jakob Schleiden a German botanist, investigated plants and conceived that plants were made up of recognizable units called cells.

• In 1839, Theodor Schwann, a German biologist, reached the same conclusion as Schleiden about animal tissue being composed of cells. • These two German biologists stated that cells are the elementary particles of organisms. • The deductions made from the observations of Schleiden& Schwann in 1839 formed the basis of cell theory. • In the year 1855 Rudolf Virchow stated that living cells arise from the pre-existing cells (Omnis cellula e cellula) . 3

• This became the the third principles of cell theory • The observations of Hooke, Leeuwenhoek, Schleiden, Schwann, and others led to the development of the cell theory. The cell theory is a widely accepted explanation of the relationship between cells and living things

cell theory

The cell theory states

• All living things or organisms are made of cells and their products. • New cells are created by old cells dividing into two. • Cells are the basic building units of life.

Exemptions to cell theory

• Virus • First formed cell • Mitochondria • Chloroplast Founders of cell theory

Fig.3. Matthias J. Schleiden( 1838 ) Theodor Schwann (1839) Rudolf Virchow(1855)

Modern Cell theory

• All known living things are made up of one or more cells • All living cells arise from pre-existing cells by division. 4

• The cell is the fundamental unit of structure and function in all living organisms. • The activity of an organism depends on the total activity of independent cells • Energy flow occurs within cells. • Cells contain DNA which is found specifically in the chromosome and RNA found in the cell nucleus and cytoplasm. • All cells are basically the same in chemical composition in organisms of similar species.

Scope of cell Biology In the 20 th century cell biology advanced by leaps and bounds, due to incorporation of genetics, organic evolution and Biochemistry into it. Discovery of electron microscope by Knool & Ruska (1931) and phase contrast by Frits Zernike (1934) brought revolutionary changes in cell Biology.

Images Fig.1. https://commons.wikimedia.org/wiki/File:Robert_Hooke_portrait.jpg

Fig.2. https://www.flickr.com/photos/martinlabar/66177481

Fig.3. https://www.sciencephoto.com/media/919572/view/jakob-matthias-schleiden-german- botanist

https://eu.wikipedia.org/wiki/Theodor_Schwann

https://en.wikipedia.org/wiki/File:Rudolf_Virchow_older_portrait.jpg

References: 1.cell and molecular biology,E.D.P.De Robertis;E.M.F.De Roberties,jr.8th edition(2004) 2.Text book of zoology-Invertebrates and cell bilogy-Telugu Academy (2013)

Prepared by

Dr.N.Ankamma,

Govt.college for women(A), Guntur