7 th Science Chapter 10.1 Cell Division and Mitosis

Cell Division All of us are made of trillions of cells Many organisms begin as one cell that divides and becomes two and eventually and so on Many celled organisms (like us) grow because cell division increases the total number of cells

Cell Division Everyday billions of red blood cells wear out and are replaced. Cell division is important to one celled organisms as well – its how they reproduce themselves.

Cell Cycle A living organisms life cycle –1. organisms formation –2. growth and development –3. death

Cell Cycle The cell cycle is a series of events that take place from one cell division to the next. –Cell cycles are not the same for all cells. –Ex. – Bean plant cells take about 19 hours to complete and an animals embryo cell completes its cycle in less than 20 minutes.

Cell Cycle In humans, cells needed for repair, replacement, or growth, like skin and bone cells, constantly repeat the cycle.

Interphase Most of the life of a eukaryotic cell (cell with a nucleus) is spent in interphase, which is a period of growth. An actively dividing cell, such as a skin cell, copies its heredity material and prepares for cell division during interphase.

Interphase Before the cell divides, a copy of the heredity material must be made so that each of the two new cells will have a complete copy. After interphase, cell division begins. –The nucleus divides and then cytoplasm separates to form two new cells.

Mitosis Mitosis – process in which the nucleus divides in cells to form two identical nuclei. Mitosis is a series of phases or steps.

Mitosis Steps of Mitosis –1. Prophase –2. Metaphase –3. Anaphase –4. Telophase

Mitosis Chromosome – structure in the nucleus that contains heredity material. During interphase, chromosomes duplicate and when the nucleus is ready to divide each duplicated chromosome coils tightly into two thickened, identical strands called chromatids.

Prophase The nucleus and nucleolus disintegrate Two small structures called centrioles begin moving to opposite ends of the cell. –Between the centrioles, threadlike spindle fibers begin to stretch across the cell. –Plant cells also form spindle fibers but do not have centrioles.

Metaphase Pairs of chromatids line up across the center of the cell Centrioles are attached to spindle fibers and they continue to move to opposite ends of the cell and stretch the spindle fibers.

Anaphase The chromatids break at the centromere and begin to separate. The centrioles continue to move to opposite ends pulling the chromosomes farther apart The separated chromatids are now called chromosomes.

Telophase Spindle fibers disappear Chromosomes begin to uncoil New nucleus forms Cytoplasm starts to divide

End of Mitosis After the nucleus has divided, the cytoplasm separates and two new cells are formed. During cytoplasm division in plant cells, a cell plate forms and in animal cells the cell membrane pinches in the middle.

Mitosis The biggest thing to remember about mitosis is that the nucleus divides and it produces two new nuclei. Every cell in your body, except sex cells, has a nucleus with 46 chromosomes.

Mitosis Each of the trillions of cells in your body, except sex cells, has a copy of the same heredity material. Cell division allows growth and replaces warn out or damaged cells We are larger and have more cells than a baby because of cell division.

Mitosis When you cut yourself, your wound heals because of cell division.

Reproduction There are two types of reproduction, sexual and asexual Sexual reproduction requires two organisms and asexual requires one organism Asexual Reproduction – a new organism is produced from one organism.

Asexual Reproduction The new organism will have heredity material that is identical to the parent. Organisms with eukaryotic cells, asexually reproduce by cell division. –Ex. – sweet potato growing in water

Reproduction Remember mitosis divides the nucleus, so bacteria is without a nucleus so they reproduce asexually by fission. Budding – type of asexual reproduction, where a new organism will begin to grow from the body of a parent.

Reproduction –When a bud becomes large enough, it will break off and live on its own. Regineration – is the process that uses cell division to regrow body parts. –Ex. – sponges, planaria, sea stars