Complete history of cell

 Cell:

         The cell is defined as structural and functional unit of life It is the smallest unit that can, carry out all activities of life. Cells are building blocks of complex multicelular organisms.  

History of Cell: 

Emergence and Implication of Cell theory: 

→ Discovery of Cell:

                                   Study of cell (e. cell biology) began with the discovery of cell by Robert Hooke in 1665, who reported hi his work in his famous publication "Micrographila." He prepared and studied thin sections of cork (consists of dead plant material) under his self-made compound microscope.

Observation of cells in a cork:

                                             Hooke observed that cork is composed of minute honey comb like compartments which he called cells. According to Hooke, cell is empty space bounded by thick walls. 

•Very little information was added to that idea is that century. 

•The work again started in beginning of 19th century.

Idea of Lorenz Oken:

                                     In 1805 a German scientist Loren Oken, stated that,

"All living beings originate from or consists of vesicles or cells." 

→Idea of De-Lamarck:

                                        In 1809, Jean Baptist  De-Lamarck stated that,         "No body can have life if its constituents parts are not cellular tissue or are not formed by cellular tissues."

→Idea of Robert Brown:

                                           In 1831, Robert Brown reported presence of nucleus in the cell. Due to this discovery, Hooke's idea about the cell as empty space was changed. It was later established that cell is not an empty space. 

→Ideas of Schwann and Scheiden:       

                                                             In 1839, a German zoologist Theodar Schwann and in 1838 a German botanist Mathias Schleiden, working independently came out with a theory called Cell Theory. They founded that cell consisted of 3 parts:

1) Nucleus

2) Fluid surrounding the nucleus (cytoplasm). 

3) Outer thin covering or membrane(plasma membrane)

 →They said, cell wall is an additional structure present only in plant cell.

Salient Features of cell theory:

                                                     Salient features of cell theory in its  present form are:

1)All organisms are composed of one or more cells. 

 2) All cells arise from pre-existing cells

(by cell division).

3) Cell is the basic structural as well as functional unit for all organisms.

Importance of Cell theory: 

                                             The cell theory is one of the most fundamental generalization in Biology. It has wide ranging effects in all fields of biological sciences.After the cell theory was presented,many details of cells were studied,so in this way cell theory was extended.

•Cells are basically similar but  extra-ordinarily versatile/different.

•Cell is not only structural but also functional unit of living organisms.

So, cell theory is very important unifying concept

 →Idea of Rudof Virchow:

In 1855, a German physician, Rudolf Virchow said that;

"New cells were formed only by the division of previously existing living cells" (by cell division).

             " Omnis Cellula e cellula".

Contrary to idea of abiogenesis: 

                                                       Virchow's idea was contrary to the  idea of abiogenesis that states:

      "Living things arise spontaneously                      from non-living things"

• It was one of prevailing but controversial ideas about origin of life at that time.

→Idea of Louis Pasteur:

                                          In 1862, one of the greatest scientist of all times, Louis Pasteur gave  experimental proof of Virchow's statement by demostrating that micro-organisms could be formed only from existing bacteria.

→ Definition of living things:

                                                Cell theory and Virchow's hypothesis gave us the basis for working definition of living organism/things:

        "Living things are chemical                        organizations composed of cells and capable of reproducing                        themselves."

→ Idea of August Weismann:

  In 1880, August Weismann said:

     "All presently living cells have a                common origin because they have          basic similarities in structure and            molecules, etc."

•It was shown that, there are fundamental similarities in chemical composition, metabolic activities and structure,although they differ in many respects.

Phenomena of viewing/Seeing the cell:

Resolution of eyes:

                                 The human naked eye can differentiate between two points, which are atleat 1mm apart. This is

called resolution of eye.This can be increased with th aid of lenses.

Resolution of compound microscope:

                                                                   In a typical compound , the resolution is 2μm, which is about 500x that of naked eye. A compound microscope is a typical laboratory microscope with at least different magnitification powers. 

•Typical occular lenses could be 5x,10x, etc. 

•Objective lenses could be 20x, 40x, 100x, etc. 

Calculation of magnification:

                                                Magnification

power of a microscope is determined by multiplying X value of occular lense and X value of objective lens .e.g: a microscope with 10x occular lens and 40x objecture less will have (10x40=400x), 400x magnifying power. •The resolution will remain the same which is 500x that of naked eye.

Source of illumination: 

• Source of illumination in compound microscope is visible light.

•Source of illumination in electron microscope is an electron beam.Its resolution ranges between 2_4 Angstorm which make it 500x greater than compound microscope and 250,000x  than naked eye. This means that two points that are 2-4 Angstrom apart can be differentiated by using electron micro-scope.  

Complexity in cellular structure:

                                                        The relevation of complexity of structure of various cellular organelle is closely linked with development of microscopy and improvement in resolution power of microscope.

Cell as a unit of structure and function:

                                                                        Cell is a unit of structure & function  in living organisms. 

Division of labour:

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 cells.

Example: 

In animals:

• muscle cells → contract and relax

• nerve cell      → transmit impulse

• gland cells    → produce secretions                                      (e.g, harmones)

• red blood cells →carry oxygen

• stomach cells   →  secrete gastric juice

In plants:

• xylem cells → conduct water and minerals from soil to aerial parts of plant.

•phloem cells →translocate food

•sclerenchymatous cells →give support to plants

•chlorenchymatous cells →carry out photosynthesis

•parenchymatous cells  →store surplus food

•meristematic cells →produce new cells for growth and development of plant.

•collenchymatous cells→ supporting cells. 

→ As different cells perform different functions, they show great variation in shape and size. 

Plan of Organization:

                                     Despite structural and functional diversity, the plant cells as well as animal cells have a common plan of organization.

 Structure of a generalized cell:

                                                      Structure of cell can be studied under light-microscope as well as electron separation. 

Techniques:

 1) Cell fractionation:

                                  Isolation / Separation of various components of a cell including organelles is called cell fractionation. In this way we can study their structure and function in detail. During cell fractionation, the tissues are homogenized on disrupted with special instruments and the various parts of the cell are separated by density gradient centrifugation.

2) Centrifugation: 

                              Isolation of cell's various parts that is achieved by spinning the homogenized or disrupted cells with special instruments (centrifuge) in a special medium at medium speeds is known as centrifugation. The various cellular parts separate out in different layers, depending upon their size, and weight and density of the medium. 

3) Ultracentrifugation:

                                      Some cellular components require very high speeds for separation from other parts of the cells. Separation of cellular components from eachother at a high very speed is called ultracentrifugation. 

Basic components of cell:

                                            A cell consists of following basic components: 

1)Plasma membrane, also cell wall in plant cell

2) Cytoplasm, containing cell organelles.

3) Nucleus, with nuclear or chromatin material 

Traditional classification system:

                                                          In the traditional classification system, all organisms are divided into:  

1) Plant cell (having cell wall)

 2) Animal cell (having no cell wall)

• Both are complex and have a distinct nucleus. (i.e: chromatin material is bounded by membrane). So, they are eukaryotic cells.

Types of organisms:

                                   With the researches of science, it was at last found that there are five types of organisms:

 1) Animals (eukaryotic)

 2) Plant(eukaryotic)

 3) Fungi(eukaryotic)

 4) Protists(eukaryotic)

 5) Bacteria(prokaryotic)

Difference between prokaryotic and eukaryotic cell:

Prokaryotic cell:

1-They do not have a prominent/definite nucleus.

2-They are 10x smaller than eukaryotic cells.

3-They do not have membrane bounded organelles except ribosomes.

4-Ribosomes size is 70S.

5-Cell wall is made up of peptidoglycan/murein.

6-Examples:

                     •bacteria 

                     •cynobacteria,etc.

Eukaryotic cell:

1-They have prominent/definite nucleus.

2-They are 10x larger than prokaryotic cell.

3-They have membrane bounded organelles.e.g:mitochondria,plastids ,golgi complex,etc.

4-Ribosomes size is 80S.

5-Cell wall is made up of:

in fungi》chitin

in plants》cellulose

6-Examples:

                      •animals

                      •plants

                      •fungi

                      •protists.

Sizes of eukaryotic cell:

                                          Eukaryotic cells vary greatly in size. They could be as big as an Ostrich's egg . Most of the cells are microscopic and are not visible to the naked eye. Their size is measured in micro-meter (μm). One micro-meter is 0.000,001 m or 1x10^-6 m.