The discovery , theory and diversity of cells
All living organisms are characterized by common characteristics such as Feeding , transporting , respiration , excretion , motion , sensation and reproduction , living organisms are divided into unicellular organisms and multicellular organisms .
In Unicellular organisms , The body consists of one cell only such as Amoeba and paramecium , In Multicellular organisms , The body consists of many cells such as Man , whale and trees .
Diversity of cells
The cell is the tiniest building unit in the organism’s body capable of carrying out all the functions of life , Cells are vary in shape , structure and size .
The biggest cell in size is the cell of the unfertilized egg of ostrich , The tiniest cell in size is the bacterial cell , The longest cell is the nerve cell ( may reach one metre ot little more ) .
There is relationship between the shape of cells and functions they perform , for example :
Nerve cells ( neurons ) are long to be able to transfer messages from spinal cord present inside the vertebral column into the most far part of the body such as the toes .
Muscular cells are cylindrical , long and accumulate with each other to form muscle fibres which can contract and relax to help man to move freely .
Cell discovery and role of scientists in discovering cell & its structure
The English scientists : Robert Hook
He invented a simple microscope ( 1665 ) and used it to screen a piece of cork . He found that it is composed of small boxed arranged in rows , He named each box by the word “ cell ” .
The term cell is derived from the Latin word ( cellula ) that means the cell or small room , Therefore the favour in cell discovery is referred to Rebert Hook .
The Dutch scientist : Antonie Van Leeuwenhoek
He made a simple microscope using lenses ( 1674 ) with the ability to magnify the objects up too 200 times of their real size , He used it for screening different substances such as water of the ponds , blood and others .
Therefore , Van Leeuwenhoek was the first to observe the world of microscopic organisms and living cells .
The German scientist : Matthias Schleiden
In 1838 , he deduced that the plants are composed of cells , He stated his deduction depending on his own researches and that of other previous scientists .
The German scientist : Theodor Schwann
In 1839 , he deduced that the bodies of all organisms are composed of cells .
The German doctor : Rudolf Virchow
In 1855 , he stated that the cell is the functional and building unit of all living organisms , He emphasized that the new cells are produced only by preciously existing other living cells .
The efforts of the previous scientists have resulted in and gave rise to what is known now as cell theory , The cell theory is considered the most important basic theory in the modern biology , This cell theory is mainly based upon three principles .
The principles of cell theory
All living organisms are made up of cells , which may be single or in clusters .
The cells are the basic functional units of all living organisms .
All cells come only from other pre-existing living cells .