History of cell biology:
Schwann is generally called the father of cell biology because he described the morphology and physiology of the cell for the first time.
The first reference on cell biology was made by Jan Swammer Dam in the year 1658. He made an account of the red blood cells of frog in 1665, Robert Hooke discovered cells while examining a piece of cork under magnifying lenses. He found that cork was made of small chambers surrounded by by walls. He called these chambers as cells.
In 1723 Leeuwenhoek studied blood cells, spermatozoa, protozoans and some other micro-organisms under his crude microscope and gave illustration about them.
Cell Biology in 19th century
This period is called as a classical period. During this period, almost all the cell organelles were discovered. The 19th century witnessed the following some important milestones in cell biology.
Cell theory:
Cell theory is a concept proposed by Schleiden and Schwann to explain the nature of cells. It states that-
- The cells are organisms.
- All plants and animals, are composed of an assemblage of cells.
- The cells arise from the pre-existing cells.
- The activities of an organism are the outcome of the activities of its individual cells.
- The cells contain nucleus which controls all activities of that cell.
Objections to cell theory:
The fallowing are the objections raised against cell theory
- Certain organisms are not made up of cells E.g. Viruses
- Certain organism do not contain nucleus. E.g. Bacteria
Protoplasm theory:
The protoplasm theory was proposed by Hertwig in 1892. This theory states that the cell comntains a viscous, colourless, translucent, colloidal substance called protoplasm. Huxley stated that it is the physical basis of life. The term protoplasm, meaning first substance, was coined by Purkinje. Felix Dujardin was the first man to observe protoplasm in 1835. He named it as sarcode. The protoplasm is also called the substance of life or the living matter.
The protoplasm has the vital force for life. It shows all the activities that characterize life. They are metabolism, movement, growth, irritability, homeostasis, adaptation and reproduction. As long as the protoplasm carries out the metabolic activities, it is alive. The moment these activities stop, it is no longer alive and soon degenerates.
Therefore, life simply means the activities of protoplasm. That is why the protoplasm is called the physical basis of life.
Germ plasm theory:
This theory was discovered by August Weismann in 1892. According to Weismann, the body of an organism formed of two types of cells, namely somatic cells and germ cells.
The cytoplasm present in the somatic cells is called somatoplasm and that present in the germ plasm. The somatoplasm dies with the death of the animal. But the germplasm alone is carried to the next generation. The germplasm is responsible for the formation of somatoplasm of the subsequent generation.
The main bulk of the body is formed of somatic cells. The somatic cells disappear with the death of the animal. So any change affecting these cells is not heritable. The reproductive cells are said to be germ cells. The germ cells are carried to the descendants, generation after generation. So any change affecting these cells is inherited.
Cell biology in 20th century
In 20th century, the field of cell biology was approached with ultra techniques. The fallowing are the some advancements in cell biology.
Organism theory:
The organism theory was proposed by Laurence Picken in 1960. It states that cell is an organism. It also states that multicellular organism is also formed of a continuous mass of cytoplasm which remains divided into small incomplete compartments, the cells. The cells are semi-independent and specialized for the various life functions. Thus, a multicellular organism is a large, highly differentiated mass of protoplasm and an unicellular organism is a small much less differentiated mass of protoplasm.
The organismal theory seems to be applicable to plants where the cytoplasm of one cell is connected to the neighboring cells by cytoplasmic strands, plasmodesmata. This theory, however, is not applicable to certain algae and fungi in which the cytoplasm is not divided into cells. This theory as a whole is generally not accepted.
