Cell Division:

why? cells wear out & must be replaced organisms grow & so need more cells when? cells have different life spans

days weeks months years Stomach lining cells Sperm cells Platelets Skin epidermal cells Lymphocytes Red blood cells Macrophages Pancreas cells Bone Cells Cell typeCell life span

Cell Cycle: The process of a cell growing and preparing for cell division

Phases of the Cell Cycle: G 1 - (Growth Phase 1) cell organelles duplicate cell grows larger

S - (Synthesis Phase) the DNA is duplicated

G 2 – (Growth Phase 2) the DNA is checked for errors cell is prepared for division

M – Phase  Mitosis a process to separate the DNA packaged in chromosomes into two identical cells

Terms chromatin  a mixture of DNA and proteins found in the interphase nucleus chromosome  condensed chromatin chromatid  one arm of a double-stranded chromosome centromere  a structure that holds two sister chromatids together single-stranded chromosome  a chromatid after it has been separated from its sister chromatid

chromatids centromere chromosome

Summary of the Phases of Mitosis: Prophase  prepare Metaphase  middle Anaphase  separate Telophase  finish Interphase  between

Prophase 1.Chromosomes condense & become visible 2. Nuclear membrane breaks down 4. Centrioles separate & move to each pole of cell 3. Spindle fibres connect the two centrioles cell membrane cytoplasm

Metaphase 1. the centrioles are at the poles 2. the spindle fibres pull the centromeres into line 3. the double-stranded chromosomes align at the cell equator 4. the centromeres now divide

Anaphase 1. the spindle fibres contract & pull the centromeres to the poles 2. the chromatids of the double-stranded chromosomes now separate 3. Now called single-stranded chromosomes they are pulled to opposite poles

Telophase 1. the nuclear membrane reforms 2. the ss chromosomes now uncoil and will disappear Cytokinesis 3. The cell membrane pinches inward 4. The result is the separation of genetic material into two identical parts

Interphase 1. The chromatin is uncoiled 2.The nuclear membrane is fully intact 4. The cell now starts to go through G 1, S and G 2 again 3. Two almost identical cells are produced

Problems with mitosis What if a cell does not stop dividing? cancer

Why is this a problem? cancer takes away things from normal cells cancer takes space cancer takes blood this means oxygen and nutrients

Now let’s look at mitosis under the microscope After we learn some things about microscpes

ocular lens course adjustment fine adjustment objective lens slide stage key parts of a microscope

only move a slide on or off a microscope with it on low power when on high power only use the fine adjustment to focus on low power, focus down and away from the objective lens with the course adjustment these microscopes are parafocal and so once they are in focus on low power, little adjustment is needed on medium or high power Rules for microscopes always use two hands to carry a microscope and do not swing it

Onion root tip Cells undergo mitosis in this section of the root tip