In the year (1839) Schleiden and Schwann have jointly proposed the “Cell Theory” It states that all living organisms are made up of cells and cells are the structural and functional units of all organisms.
Development of Cell Theory
If we study the step by step development of cell theory we will understand how scientific methodology operates. It includes the following steps
3. Formulation of theory
4. modification of theory ( if it warrants). Observations were made by Schleiden (1804 -1881) a German botanist.
He examined a large variety of plants and found that all of them were composed of cells. In 1838 he concluded that cells are the ultimate structural units of all plant tissues. Schwann a German Zoologist studied many types of animals and found that animal cells lack a cell wall and they are covered by a membrane. He also stated that animal cells and plant cells were basically identical but for the cell wall.
He observed that both contain nucleus and a clear substance around it. He defined the cell as a membrane bound nucleus containing structure. He proposed a hypothesis that the bodies of animals and plants are composed of cells and their products. Schleiden and Schwann both together discussed Schwann’s hypothesis and they formulated cell theory.
The important aspects of cell theory are:
1. All living organisms are made up of minute units, the cells which are the smallest entities that can be called living.
2. Each cell is made up of protoplasm with a nucleus and bounded by plasma membrane with or without a cell wall.
3. All cells are basically alike in their structure and metabolic activities.
4. Function of an organism is the sum total of activities and interaction of its constituent cells.