write the comparative table for two modes of cell division
Answers
Cells can divide by either mitosis or meiosis. Both of these are preceeded by the interphase.
Interphase consists of three stages: the G1 stage, the S stage, and the G2 stage. During the G1 phase all the internal organelles of the plant cell are replicated, during the S phase (the longest phase) all the DNA of the plant cell is replicated, and during the G2 phase the replicated DNA is checked for mutations. This process is necessary prior to mitosis to ensure that the cell has twice the usual amount of organelles and twice the usual amount of DNA to ensure that two genetically identical diploid cells can be produced when the cell divides by equatoral division in mitosis.
Mitosis consists of prophase, metaphase, anaphase, and telophase, followed by cytokinesis.
During prophase, the nucleolus disappears, the nuclear envelope breaks down (dissociates completely), membranous organelles scatter towards the periphery of the cell, the chromatin continues to condense so each replicated homologous chromosome in a pair becomes visible as two sister chromatids joined at the centromere (each of a pair of homologous chromosomes, one paternal and one maternal, that contain the same amount and sequence of DNA/same genes but may have different alleles and are not functionally equivalent, is replicated in interphase and consists of two identical sister chromatids), the microtubules form a 3D structure called the spindle, and centrioles move to opposite ends/ poles of the cell and organise the spindle into spindle fibers. Finally, replicated homologous chromosomes move towards the equator of the cell and spindle fibers start extending towards the equator of the cell.
During metaphase, the replicated DNA lines up in single file along the equator of the cell and spindle fibers attach to the chromosomes at the centromere.
During anaphase the spindle fibers shorten, pulling the two sister chromatids of each replicated homologous chromosome towards opposite ends of the cell. Therefore sister chromatids, now referred to as chromosomes, are pulled to opposite poles (centrioles) of the cell.
Telophase is the opposite of prophase; two new nuclear envelopes start to reform, and two nucleoli reappear. Replicated membranous organelles arrange themselves in the correct position in two separate areas of the cell, as the cell expands giving it a stretched look (two new cells start to become visible), the chromatin unravels into thin strands of DNA, the spindle fibers break down, and the centrioles move away from the poles of the cell.
The last stage is cytokinesis, which is the splitting of the cell membrane to form two new cells after the cytoplasm divides. In plant cells this is done by synthesising a new cell plate in between the two nuclei, which becomes a part of the new cell wall of each genetically identical daughter cell as the cytoplasm divides and the two cells split.
The cell cycle (interphase) and mitosis are vital in both plant and animal cells as they allow growth and repair and asexual reproduction to occur.