One of the basic principles of biology is cell theory. The cell theory was initially proposed in the mid-19th century. It claims that cells make up all living things and are the primary fundamental, structural, and organisational unit of all living creatures. It also claims that all cells develop from pre-existing cells.
German scientists Matthias Schleiden (1804-1881), Rudolph Virchow (1821–1902), and Theodor Schwann (1810-1882) are credited with developing this theory.
Modern cell theory was proposed to address the limitations of traditional cell theory. Many experts, including biologists and physiologists, offered the modern cell theory as a conclusion to all cell research. Scientists can now accurately view the components of cells under a microscope because of advancements in microscopy magnification techniques.
Parts of Cell Theory
Three main concepts of cell theory are:
- First, cells make up all living things.
- Second, cells serve as the fundamental building blocks for the development of all the tissues, organs, and components of a living organism.
- The third and most important aspect of the hypothesis is that new cells can only develop from pre-existing ones.
German biologists Matthias Jakob Schleiden and Theodor Schwann proposed the first cell hypothesis in 1838 and 1839, respectively. According to Schleiden, cells are the building blocks of or the products of cells in every structural component of a plant. According to Schwann, the structures of both plants and animals are composed of cells or their byproducts.
Limitations of Classical Cell Theory
The limitations of cell theory include the following:
- Schleiden and Schwann were unable to describe the basic structure of viral cells. They claimed that a coordinated cell function constitutes the body. However, this is untrue in the event of viruses because the viral machinery primarily activates within the host (bacteria, animals, and plants). For the duration of its life cycle, a virus requires host machinery.
- Prokaryotic organisms lack a distinct nucleus in their cells. Cell theory consequently fails in this instance as well.
- The cell theory states that each cell has “a nucleus”, although some cells, such as tapetal cells, are multinucleated or coenocytic.
- The cell theory states that every cell has a nucleus; however, some cells, like human RBCs and angiosperm sieve tubes, do not.
Modern Cell Theory
The combined efforts of various scientists led to the development of modern cell theory. Modern cell theory has two basic objectives: all cells primarily originate from some other cells (biogenesis principle). Cells and their byproducts are the essential building blocks of organisms.
The commonly accepted components of modern cell theory include the following:
- The cell is the fundamental, structural, and functional building block of all living organisms.
- Every cell in the body develops or evolves from pre-existing cells.
- The independent cell’s activity affects the activity of the entire organism.
- Cells are where the energy is transferred (biochemistry and metabolism).
- The different individuals of similar species share the same cellular components.
- Chromosomes and DNA molecules store genetic data. Cells communicate with one another by sharing genetic information.
- Organisms of similar species share similar chemical composition in their cells.
Chromosomal Theory of Inheritance
The chromosomal theory of inheritance was put forth independently by Walter Sutton (1902) and Theodor Boveri (1903) in independent studies. According to this theory, specific gene positions on particular chromosomes correspond to particular genes, and the chromosomal behaviour during meiosis could explain why genes are inherited following Mendel’s laws.
The following findings support the chromosomal theory of inheritance:
- In an organism, chromosomes are found in matched (homologous) pairs, like Mendel’s genes. Each member of a pair—chromosomes and genes—comes from each parent.
- Each sperm or egg gets one member because the homologous pair separates during meiosis. In Mendel’s law of segregation, the separation of alleles into gametes is mirrored by this mechanism.
- Like the alleles of various genes in Mendel’s law of independent assortment, members of different chromosomal pairs are sorted into gametes independent of one another during meiosis.
Before there was any concrete proof that characteristics were carried on chromosomes, the chromosomal theory of inheritance was put out and was controversial. In the end, it was verified by the research of geneticist Thomas Hunt Morgan and his associates, who studied the genetics of fruit flies.
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