The cell is the basic structural and functional unit of life. The cell is the simplest and smallest unit capable of carrying all life activities.In the unicellular organism, a single cell performs all the life activities. Hence, a cell is considered as the structural and functional unit of life. Cell biology is the biology which deals with the structure and function of cells.
Discover of cell
R. Hooke first observed cell under the microscope. The kind of cell he observed is plant cell(dead cells) eg; cork cell. He gave the term cell where the cell is the hollow space or chamber. A.V. liver hook first observed living cells. eg; protozoans R.B.C. sperm cells. M.J. Schledemand T. Schwann is formulated cell theory.
Cell theory or Cell Principle
Statement of cell theory
All the living organisms are made up of the cell and their products.
Cells are the basic, structural unit of life.
All the cells are basically similar in structure and chemical composition.
A cell is a small mass of protoplasm containing a nucleus, cytoplasm, cell organelles and remains covered by the cell membrane.
The functions of living organisms are the result of functions and interactions of cells constituting the body of that living organism.
All new cells arise or originate from pre-existing cells. This statement was first given by R. Virchow.
The life passes from one generation to another in the form of a living cell called gametes.
Genetic information is stored and expressed inside the cell.
The growth of organisms depends on upon cell division and cellular growth.
Expectations to Cell theory
Viruses: Because they do not have a cellular structure.
Bacteria and blue-green algae or cyanobacteria: Because they do not have a true or membrane-bounded nucleus.
Coenocytic structure (multinuclear cytoplasm) eg; hypha of mucor bread mold.
RBC: Because it lacks the nucleus.
The Cellular Totipotency
It refers that every living vegetative part of living plants has got all the potentialities to grow into a new plant. It was first stated by German botanist Haberlandt ( 1902 ) but later it was proved experimentally by F.C. Steward and his co - worker in 1950.
At first, they took small pieces from phloem tissue of carrot roots composed of matured non-living cells and put in a liquid nutrient medium having coconut milk.
Cell cluster became free from each other after shaking the medium gently.
Some of them multiplied and formed rooting clumps.
Cell cluster was then transferred to another tube containing semi-solid medium of the same composition.
Here, a new plant was formed which was then transferred into the pots and was developed into the flowering plants.
From this experiment, Steward concluded that even mature cells when separated from the plant body, have the capacity to develop into new plants. This was referred to as cellular totipotency.
Important structure of unicellular organisms
The cell is large and consists of organelles that are necessary for the life processes.
The cell has to be sufficiently large to accommodate the numerous organelles. Unicellular organisms have certain limitations of size and shape.
A unicellular organism can not exhibit the wide range of differentiation, which leads to greater efficiency.
Any injury to the cell may lead to the death of the organism. They are susceptible to damage.
The cell size ranges from 11µm to 1mm.
Important structure of multicellular organisms.
The body consists of many cells and different cells carry out different functions.
The cells of multicellular organisms are differentiated to perform specific functions.
They have better adaptability or have a greater capacity for survival as the dead and worn out cells are continuously replaced by the new cells.
They are more efficient and carry out the number of activities with the help of different kinds of cell.