Cell theory Protoplasm theory Page 3

Cell theory and Protoplasm theory: Page 3

Cell Theory

  • H. J. Dutrochat (1824) boiled the tissues in acid and separated the cells. On that basis he concluded that all animals and plants are made up of cells.
  • M. J. Schleiden (1838) found that all plant cells have essentially similar structure.
  • T. Schwann (1839) observed that animal cells do not have cell wall.

Schleiden and Schwann (1839) compared their findings and formulated cell theory which is as below.

  • All plants and animals are made of cells. The cell is the basic structural and functional unit.
  • A cell is a mass of protoplasm having a nucleus.
  • Cells are similar in basic structure and metabolism.
  • The new cells are formed by a process similar to the crystal formation.

Virchow (1858) stated that the new cells originate from the pre-existing cells only “omnis cellula e cellula”. The main features of the cell theory as known today are as follows:

  • All living organisms are composed of cells. Thus, cell is the structural unit of living organisms.
  • All cells arise from the pre-existing cells of the similar kind. Thus, cell is the unit of heredity.
  • The chemical composition and metabolism of all cells is basically alike.
  • All living cells arise only from already existing cells by cell division.
Exceptions of Cell Theory

  • Virus: In virus Protoplasm and nucleus are absent while DNA and RNA is the genetic material.
  • Bacteria and Blue-green Algae: They are No true cells, nuclear membrane is absent and therefore, the nuclear content is in direct contact with the cytoplasm.
  • Some mould Fungi: Body is having undivided mass of protoplasm in which numerous nuclei are scattered called coenocytes.

Protoplasm Theory

    • This theory was proposed by Max Schultze in (1861) stating that cells were nucleated protoplasm or the physical basis of life. The protoplasm is the important constituent of life and not the cell wall.
    • Strasburger in 1884 observed that the nucleus is associated with the inheritance of the genetic characters.
    • Purkinje proposed the name protoplasm to the entire substance found in the cell which is most important biological substance.
    • All important activities are carried out only due to protoplasm.
    • Huxley (1868) called protoplasm as the physical basis of life.

Physical properties of Protoplasm

  • It is a complex jelly like granular elastic colorless substance.
  • It changes form from Sol to gel and vice versa
  • The inner environment is always in rapid motion called Browian Movement. Thus, the molecules of protoplasm always show streaming movement
  • Protoplasm responds to various stimuli like light, chemical, temperature etc.

Chemical nature of Protoplasm

  • It is composed of both organic and inorganic chemicals
  • Inorganic Substance: 70 % water, 30% elements  (C, H, O, N, Na, K, P, Cl, CO3, etc.)
  • Salts and gases (CO2 and O2 are in dissolved state) are also present.
  • Organic Substance: Carbohydrate, Fat, Proteins, Nucleic Acid, Enzymes etc.
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