Cell Theory: Important Characters & it’s 4 exceptions
The cell is the smallest unit of life. Since the origin of the cell, it has evolved from a unicellular to a multicellular and acellular (partially unicellular or multicellular) structure. The cell is considered the smallest entity in a living system. There are several theories have been given to explain the formation and evolution of cells. Cell theory by the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann explained the characters of the cell.
There are four distinct characters defined for cells. The first three are given in the late 1830s, by botanist Matthias Schleiden and zoologist Theodor Schwann and the fourth one is given by German pathologist Virchow.
Characters of cell:
1) Structural unit:
A cell is a structural unit of an organism. Every cell has its own specific structure which includes cell organelles, cytoplasm and plasma membrane as an outer protective structure.
2) Functional unit:
The cell is the functional unit of an organism. Each cell is functionally independent, as each of them has its own metabolism their own genetic structure etc.
3) Hereditary unit:
A cell is a hereditary unit of an organism. Each cell has its own genetic material. In the case of a eukaryote, it is specifically enclosed in a double membrane spherical structure called the nucleus. While in the case of prokaryotes it is suspended freely into the cytosol.
The theory of biogenesis explains every cell arises from its pre-existing cell. A single living cell behaves as a maternal cell and can divide and form two daughter cells. Then these two daughter cells have the ability to undergo division. The formation of new cells from pre-existing cells is called biogenesis. Where ‘Bio’ means life and ‘Genesis’ means synthesis. The theory which gives an idea about the formation of new cells from pre-existing cells is known as the theory of biogenesis.
But as we know that life science is incomplete without exceptions. Hence cell theory also has 4 exceptions with respect to their four characters.
Exceptions of cell Theory:
A cell is a structural unit, which has its specific solid structure with the help of which it can multiply itself. But viroid is any molecule, consisting of about 150 to 200 nucleotides in their structure. Which acts as an infectious RNA and infects plants. They don’t have any proper structure still they can multiply their number. Hence the presence of viroid is an exception for cells as a structural unit.
2) Virus :
Viruses are the best exception for cells as functional units. Viruses are obligate parasite which lacks their own metabolism. As it lacks its own metabolism it requires the host’s metabolism for its survival. So we can’t culture viruses as they lack their own metabolism, hence viruses are not functionally independent.
The cell is considered a hereditary unit, but there are few cells which lack genetic material in them. RBCs are one of them. RBC lacks nucleus hands it won’t have any kind of genetic material so they can’t inherit their genetic material. Even the WBC’s B cells specifically undergo genetic rearrangement, hence also lacking genetic equivalence in the genome. So these can’t be considered hereditary units.
4) Abiogenesis :
The theory of biogenesis can explain the formation of existing cells from the pre-existing cell. But when we look at it from the original point of you. The origin of the first cell remained unanswered. The origin of the first cell can be explained with the help thermogenesis process in chemosynthetic theory. Hence the origin of the first cell becomes an exception for the Theory of biogenesis.
After understanding the Cell theory and Exceptions of cell theory if you want to attempt some more Life Science test series ??? Then try this :
- Cell Biology Test 1
- Ecology Test 1
- Biochemistry Test 1
- Plant Physiology Test 1
- Molecular Biology Test 1
- Developmental biology Test 1
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