The Cell Division – In 1855 AD, Virchow first clarified that new cells are born from already existing cells. The main function of cell division is to give rise to many daughter cells from one cell. (The Cell Division) These cells play an important role in physical growth, regeneration of damaged tissues, growth of new organs and sex-asexual reproduction in humans and other animals. Generally two types of cell division are seen which are known as Mitosis and Meiosis. Apart from this, another cell division is also found which is called mitosis.
Mitosis: This division is seen in primitive organisms, bacteria, fungi, protozoa, algae etc. It is also called direct nuclear division. In this, the nucleus first becomes elongated then splits directly into two parts and separates. A daughter nucleus reaches each part.
Cell Division
Mitosis: It is also called indirect cell division. The term mitosis was first used by Walther Floming in 1882 AD. He named cell division as mitosis which means thread like formation. (The Cell Division) Actually mitosis means division of nucleus, but in practice the term is used for division of both nucleus and cytoplasm. This type of cell division occurs in the somatic cells of the body. In this type of division, the mother cell divides to form two identical new daughter cells. (The Cell Division) Mitosis cell division is a continuous process. Mitosis is a complex process that takes place in several stages or stages. For ease of study, mitosis can be divided into five stages or stages-
(i) Resting stage or Interphase: Every cell is in resting phase before the start of mitosis. In this stage chromosomes are not clearly visible due to the cell being hydrated. In this stage, the chromatin network remains diffused in the nucleus, but gradually this nucleus-net becomes apparent.
(ii) Prophase: As soon as mitosis starts, dehydration starts in the cell. As a result, the cell and then the chromatin network are also clearly visible. (The Cell Division) After this, the threads of the chromatin mesh break and get converted into many small pieces. go. These fragments are chromosomes. Granular structures are visible on each chromosome called chromomeres. Initially the chromosomes are slightly longer. Each organism has a fixed number of chromosomes in its cells.Each chromosome has a specific location called the centromere. After this, the length of the chromosomes is divided into two halves, but both the halves remain attached to each other at the centromere. Each half-part is called a chromosome or chromatids. Centrosome in animal cell divides into two parts and moves to both the poles of the cell. Many Astral rays come out around each star body. There is some change in the cytoplasm between the two stellate bodies. As a result, spindle fibers are formed between the two star bodies. After this the chromosomes shrink and become shorter and thicker. In plant cells, filamentous threads are formed but stellate bodies are not found. Gradually the nuclear membrane begins to disappear and the chromosomes move to the center of the cell. With the disappearance of the nuclear membrane, the prophase stage is completed.
(iii) Metaphase: In this stage of mitosis, the spindle becomes fully developed. The middle part of the argument is called the intermediate line. Chromatids of a chromosome become more pronounced than before. Each chromosome is shifted and arranged at the intermediate line of the spindle. Chromosomes are attached by their centromere to the spindle threads.
(iv) Anaphase: At the beginning of this stage of mitosis, the centromere of each chromosome divides into two parts. As a result, the chromatids of each chromosome are now separated. A kind of repulsion arises between the two chromatids of each chromosome. Due to this both the chromatids start moving away from each other. A kind of stretch is also created in the thread, due to which the thread starts shrinking gradually. Therefore, the contractility of the spindle threads helps to move the chromatids away from each other. As a result of this stretch, both the chromatids reach both the poles of the cell. The shape of the chromosomes becomes ‘V’ or ‘U’. Now each chromatid is called the daughter chromosomes.
(v) Telophase: In this stage the progeny chromosomes move in the opposite direction and reach near the star body on their side. Now the prophase in the daughter chromosomes present in each cell pole
The exact opposite reactions occur. As a result, hydration starts in the chromosomes, due to which the chromosomes gradually become thinner and longer and they are not clearly visible. Nucleolus reappears. Simultaneously, the nuclear membrane around the chromosomes is re-formed. Thus two daughter nuclei are formed from one mother nucleus.
Cytokinesis: After the division of the nucleus, the division of the cytoplasm takes place which is called cytokinesis. In fact, the division of cytoplasm begins from the anaphase stage itself. At the end of telophase, the cytoplasm begins to protrude inwards from the middle, causing a contraction. (Cell Division) Gradually, the inner wall of the cytoplasm increases. (The Cell Division) As a result the cytoplasm divides into two parts and finally the cell divides completely. In this way two cells are formed from one cell.
