Reproduction and Cell Division (8) Reproduction and Cell Division (5.8) Reproduction and Cell Division (5.8) The Cell Cycle and Mitosis (5.5) The Cell Cycle and Mitosis (5.5)

The Cell Cycle Division Phase: Division Phase: Prophase Metaphase Anaphase Telophase Interphase Interphase

What is and is not Mitosis? Mitosis is nuclear division plus cytokinesis, and produces two identical daughter cells during prophase, metaphase, anaphase, and telophase. Interphase is often included in discussions of mitosis, but interphase is technically not part of mitosis.

Interphase The cell is engaged in metabolic activity and performing its prepare for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible. The cell prepares for cell division by duplicating its genetic material.

Prophase Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes. The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle.

Metaphase Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.

Anaphase The paired chromosomes separate and move to opposite sides of the cell. The two halves move to opposite poles of the cell. If anaphase proceeds correctly, each of the daughter cells will have a complete set of genetic information

Telophase Chromosomes arrive at opposite poles of the cell, and new membranes form around the daughter nuclei. The chromosomes disperse and are no longer visible under the light microscope. The cytoplasm and organelles separate into roughly equal parts, and the two daughter cells are formed.

Cytokinesis In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts, pinching the cell membrane in the middle and forming two new daughter cells. In plant cells, the rigid wall requires that a new cell wall forms along the middle, creating two new cells.

Reproduction and Cell Division Reconsider the modern cell theory:  All living things are made up of one or more cells.  The cell is the functional unit of life.  All cells come from pre-existing cells. Cell division, the process by which cells come from pre-existing cells, is the process that perpetuates life and allows species to continue. Just as cells reproduce as part of the cell cycle, living organisms reproduce as part of their life cycle.

Note that some organisms use both methods of reproduction. For example, bacteria reproduce mostly in an asexual process called binary fission, which is basically cell division as you have learned it. However, bacteria are also able to exchange genetic information in a form of sexual reproduction. Similarly, most plants reproduce sexually, in the process that results in seeds, but many also reproduce asexually in various other ways.

Reproduction of Cells