Cell division is the process by which a parent cell divides into two or more daughter cells.Upon completion of the process, each daughter cell contains the same genetic material as the original cell and roughly half of its cytoplasm. Among prokaryotes, cell division occurs by simple fission. Among eukaryotes, the cell nucleus divides first, and then a new cell membrane is formed between the nuclei to form the new cell. Cell division is used as a means of reproduction in organisms that reproduce asexually, as by fission or spore formation, and sexually reproducing organisms form gametes through cell division. Cell division is also the source of tissue growth and repair in multicellular organisms. The two types of cell division in eukaryotic organisms are mitosis and meiosis.
Why is cell division necessary ?
One of the most important characteristics of living being is its ability to reproduce. Growth involves increase in the size of organisms and increase in the number of cells. Cell division is the process through which this is achieved. The new cells arise from pre existing cells only through the process of cell division.
In unicellular organisms too cell division is a means of reproduction and population growth. Two or more daughter cells are produced by cell division. Multi-cellular organisms are made up of millions of cells. For example,there are 26 billion cells in a newborn baby and 50 trillion cells in an adult. In all multicellular organisms, life starts from a single cell i.e., zygote. Zygote is the product of union of male and female gametes. Zygote divides and re-divides to produce a complex multicellular organization. After each division, there is a gap period in which cells take nutrients from their surroundings and convert them into the living substance, protoplasm. The cells in plants divide throughout the life of the plant. However, in animals, cell division stops after a certain age, but takes place when cell division is required to replenish damaged cells. Growth and development result from this action.
Types of Cell Division :
Cells divide by three different methods – amitosis, mitosis and meiosis. In amitosis, spindle fibers are not formed. Mitosis is the type of cell division which takes place in somatic (body) or vegetative cells. It takes place during growth and asexual reproduction of plants and animals. It is also known as somatic (soma means vegetative body) cell division. Meiosis is the type of cell which takes place in reproductive found in gonads of organisms. This process can be observed during gametogenesis i.e., formation of gametes (eggs and sperms).
What happens during Cell Division ?
A cell has broadly two parts: nucleus and cytoplasm. In cell division both parts divide successively. The division of nucleus is called nuclear division or karyokinesis (karyon means nucleus). This is followed by the division of cytoplasm which is known as cytokinesis. The processes of mitosis and meiosis are complicated and are studied in different steps.
What is Cell Cycle ?
The cell cycle is the life cycle of a dividing cell.It is the series of events involving the growth, replication, and division of a eukaryotic cell. It includes Interphase and the M phase or Mitotic phase (mitosis and cytokinesis).The sequence of events within the cell between mitotic (cell) divisions. The cell cycle is conventionally divided into five phases: G0 (the gap); G1, (the first gap or growth phase); S (the synthesis phase, during which the DNA is synthesized and replicated); G2 (the second gap or growth phase); and M (mitosis). Cells that are not destined to divide again are considered to be in the G0 phase. The transition from G0 to G1 is thought to commit the cell to completing the cell cycle by dividing.
Details : Howard and Pelc divided the cell cycle into four intervals: G1, G2, and mitosis. G refers to gap and S refers to synthesis.in the G1 (gap one) period, a cell has to make a critical decision as to whether it should divide or remain as such. If a cell has passed the checkpoint of G1, it enters a phase of DNA duplication. This phase is called S phase. The mass of DNA is doubled upon the completion of S phase. The next phase is G2 phase. In this phase RNA synthesis occurs, which in turn leads to synthesis of proteins needed during mitosis. After the completion of G2 phase, the cell enters the mitotic phase marked by prophase. G1, S, and G2 are included within the interphase.
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