Cell Fundamental Unit of Life

CELL-:

A Cell is the basic Structural, Functional, and biological unit of all known Living Organisms. 

A cell is the Smallest Unit of life that can replicate independently, and cells are often called the "Building Blocks of Life".

Cell are responsible for providing a definite structure to the body and for converting nutrients into energy.

A cell consists of different components which help the cell to run properly called Cell Organelles each of them has a unique set of functions.

Our body contains different types of cells like muscle cells, nerve cells, etc. having different structures.

 Discovery of Cells

Robert Hooke discovered the cell in 1665. Robert Hooke observed a piece of  cork under a compound microscope .and discovered honey comb like structure Consequently, he named these structure as cells. However, his compound microscope had limited magnification, and hence, he could not see any details in the structure. Because of this limitation, Hooke concluded that these were non-living entities.

Later Anton Van Leeuwenhoek observed cells under another compound microscope with higher magnification and he had noted that the cells exhibited some form of movement (motility). As a result, Leeuwenhoek concluded that these microscopic entities were “alive.” 

In 1883, Robert Brown, a Scottish botanist, provided the very first insights into the cell structure. He was describing the nucleus present in the cells.

Theodore Schwann - zoologist who observed that the tissues of animals had cells (1839)

Mattias Schleiden - botanist, observed that the tissues of plants contained cells (1845)

Rudolf Virchow - also reported that every living thing is made of up vital units, known as cells. He also predicted that cells come from other cells. (1850)

SOME IMPORTANT DISCOVERIES:

• Antonny Von Leeuwenhoek in 1673-1674 observed bacteria, spermatozoa, RBCs etc.
• Alfonso Corti in 1772 observed living matter in the cells.
• F. Fontana in 1781 discovered nucleolus in skin cell of eel. 
• Dujardin in 1835 discovered living semi fluid substance of cells and named it sarcode.
• M.J. Schleiden and Theodore Schwann in 1838-1839 propounded cell theory. 
• J.E. Purkinje and von mohl in 1839 coin the term protoplasm (supported by Von Mohl)

CELL THEORY

The "Cell theory" was developed later by "Rudolf Virchow" and was originally proposed by two biologists, "Schleiden and Schwann". 

According to cell theory,

• All plants and animals are composed of cells.
• Cell is the basic unit of life.
• All cells arise from pre-existing cells.
• Viruses are the exceptions of cell theory.

TYPES OF CELL 

On the basis of type of organization, cells are two types:

Prokaryotic cells:

1. These are primitive and incomplete cells. 
2. They have less developed nucleus without nuclear membrane & nucleolus.

3. some prokaryotes such as bacteria have a region within the cell.

   where the genetic material is freely suspended. This region is called the nucleoid.

4. They all are single-celled microorganisms.
5. The cell size ranges from 0.1 to 0.5 µm in diameter.
6. The hereditary material can either be DNA or RNA.
7. Prokaryotes reproduce by binary fission, a form of sexual reproduction.

e.g.  Bacteria, archaea bacteria and cyanobacteria.

Eukaryotic cells: 

1. These are well developed cells. They have advanced nucleus with unclear membrane and nucleolus.
2. Eukaryotic cells are characterised by a true nucleus.
3. The size of the cells ranges between 10–100 µm in diameter.
4. This broad category involves plants, fungi, protozoans, and animals.
5. The plasma membrane is responsible for monitoring the transport of nutrients and electrolytes in and out of the cells.It is also responsible for cell to cell communication.
6. They reproduce sexually as well as asexually.

e.g.  Plants & animal

TYPES OF ORGANISM 

Based on number of cells. These are of two types:

Unicellular organisms: The organisms which are made up of single cell. This single cell performs all the vital activities of an organism.

 e.g. Amoeba

Multicellular organisms: The organisms which made up of many cells. These cells then combine to form tissue, group of tissues form an organ and group of organs performing different functions forms an organ system which cluster forms an organism. 

e.g. plants and animals

Both plant and animal cells are eukaryotic, However, plant cells and animal cells do not look the same or have all of the same organelles but some there are some differences in their structure and organelles.

Plant cell:

• They are eukaryotic cells having a true nucleus along with specialized structures known as organelles which perform specific functions.
• Fixed size which is generally larger. The normal range is from 10-100 micrometres.
• They have a fixed and rigid shape – generally rectangular or cubical.
• Has a cell wall composed of the cell membrane and cellulose.
• Rigid wall cell and plasma membrane
• Plant cells exposed to sunlight posseses chlorophyll containing plastids called chloroplasts.
• Ribosomes are Present      
• Nucleus is lies on one side in the peripheral cytoplasm due to central vacoule 
• Cilia are absent.      
• Centrioles are absent.       
• Mitochondria are Present in a small number. 
• Glyxoxysomes may be present.   
• Lysosomes are absent.      
• Centrosomes are absent. 
• Vacuoles are generally large and provide structural support to the cell.
• Plant cells can synthesize essential nutrients their own such as amino acids, vitamins coenzymes that are required by the plant.      
• Reserve Food is generally starch and fat

Animal Cell:

• It is a type of eukaryotic cell that lacks a cell wall and has a true, membrane-bound nucleus along with other cellular organelles.
• Irregular and small in size. Ranges from 10-30 micrometres.
• They have round and irregular shapes.
• Does not have a cell wall
• Flexible and thin plasma membrane
• Plastids are usually absent.
• Chlorophyll is absent.
• An animal cell may have many small vacuoles.
• Nucleus lies in the centre.
• Mitochondria are generally numerous.
• Centerioles are found in animal cells.
• Glyoxysomes are absent.
• Animal cell cannot synthesise certain aminoacids,fatty acid ,vitamins and coenzyme
• Reserve food is usually glycogen and fat.