Mitosis - Cell Division

Living organisms have life cycles. Life cycles begin with organism’s formation, followed by growth and development and end in death.

Individual cells have life cycles. The time it takes to complete the cell cycle varies depending on the type of cell. Some cells constantly complete the cycle, others take hours or longer. Cell cycle is broken down into sections

Interphase The longest part of a cell’s life cycle Several major things occur during Interphase; The cell grows, develops. Organelles are duplicated. The DNA is copied (chromosomes duplicated) The cell prepares for cell division. Interphase is NOT part of mitosis.

Interphase

Mitosis Mitosis is the process in which the nucleus divides to form two identical nuclei. This process is described in a series of phases or steps. The steps ( in order) Prophase, Metaphase, Anaphase and Telophase. During Interphase each chromosome in the cell duplicates. When the nucleus is ready to divide, each duplicated chromosome coils into two thickened strands called chromatids.

Chromatids

Prophase First phase of mitosis Chromatids are fully visible under a microscope Nucleolus and nuclear membrane disintegrate Two small structures called centrioles move to opposite ends in the cell. Between the centrioles, (found in animal cells only) thin threadlike structures called spindle fibers begin to stretch across the cell.

Prophase

Metaphase The chromosomes line up across the midline of the cell. The centromere of each chromosome becomes attached to two spindle fibers.

Metaphase

Anaphase The centromere, in the center of each pair of chromatids, splits in half. The spindle fibers shorten, pulling the pair of chromatids apart. Each pair of chromatids separate, and move to opposite ends of the cell.

Anaphase

Telophase Spindle fibers disappear. Nuclear membrane reappears. Chromosomes begin to uncoil and a new nucleus forms.

Telophase

Cytokinesis Division of the cytoplasm In animal cells – the cell membrane pinches in the middle. In plant cells – a cell plate forms followed by the formation of new cell walls. After Telophase, cells enter into Interphase.

Cytokinesis

Results of Mitosis Two Important things to remember: Mitosis is the division of a nucleus. The process produces two new nuclei that are identical to each other and to the original nucleus. Every cell in your body – except reproductive cells, has 46 chromosomes – 23 pairs. Cell division allows for growth and replacement of worn out or damaged cells.

Asexual Reproduction A new organism is produced from one organism. The new organism has exactly the same hereditary material as the parent organism.

Asexual Reproduction in Plants

Asexual Reproduction in Animals