Transcript Chapter 5
Mitosis is the Basis of Asexual Reproduction Growth rate of a cell Task: Complete Activity 5-1A on page 138 Cell Cycle The life of a cell is known as the cell cycle. Cells die and are replaced at about the same rate in most cases of cell division. Not all cells divide at the same rate The cell cycle occurs in somatic (body) cells and consists of 3 stages: Interphase Mitosis Cytokinesis Stage 1: Interphase: The longest stage of the cell cycle Cells carry out the function needed for survival and cells that divide prepare for reproduction During the 1st part of interphase, the cell is increasing in size and making necessary proteins and molecules to maintain cell function. Organelles begin to duplicate. During the 2nd part of interphase, DNA is being replicated During the 3rd part of interphase, cell continues to grow and makes more proteins Stage 2 Mitosis: The process of cell division that results in growth and/or cell replacement of all cells of the body (except for egg and sperm cells) The shortest stage of the cell cycle During this stage, the contents of the cell’s nucleus divides, resulting in two daughter cells that are identical to the parent cell (Important!!!) As the nucleus prepares to divide, the DNA that replicated during interphase joins together to form the sister chromatids of a chromosome. Stage 3 Cytokinesis: The final stage of the cell cycle The two nuclei are separated into two daughter cells that are identical to the original parent cell In animal cells, the cell membrane pinches together to form two cells. In plant cells, a cell plate forms along the center of the cell to divide the cell into two daughter cells Cytokinesis Stage of Mitosis: Prophase, Metaphase, Anaphase and Telophase (PMAT) Prophase Double stranded chromosomes shorten and thicken and the membrane around the nucleus begins to fade Metaphase X-shaped chromosomes are lined up at the equator of the cell Anaphase The sister chromatids are pulled apart and move to opposite poles of the cell. Each sister chromatid is now considered to be a chromosome Telophase One complete set of chromosomes is now at each pole. A membrane forms around each set of chromosomes. Now there are two nuclei in one cell and the new cells are ready to divide Mitosis Flashback Remember: Mutagens can disrupt and interfere with mitosis. The effect of radiation on cells can be that chromosomes fail to move to the opposite pole of a cell during anaphase. (page 146, Figure 5.12). Cells do not divide and reproduce properly, the result can be cancer formation Observing Chromosomes Chromosomes are not normally visible under a light microscope unless the cell being observed is in the process of dividing. Task: Activity 5-1C, Observing the Cell Cycle in Plant Cells Websites: to observe, identify and describe a cell nucleus undergoing cell division and chromosomes during each stage of mitosis. http://www.cellsalive.com/mitosis.htm http://www.cellsalive.com/cell_cycle.htm http://esminfo.prenhall.com/science/BiologyArchive/audesirk/close rlook/mitosis.html Asexual Reproduction Only one parent is required to produce offspring and the offspring looks identical to the parent and to each other. The production of clones. There are 5 types of asexual reproduction 1. Binary Fission A single parent cell replicates its genetic material and divides into two equal parts Examples: algae, amoeba, protozoa Diatoms Paramecium 2. Budding Occurs when part of the parent pushes outward to form an outgrowth or bud The bud then pinches off from the parent cell to become identical to the parent Example: yeast, hydra, and spider plant Yeast Hydra Budding… Spider Plant 3. Fragmentation If an organism breaks apart as a result of injury, each fragment then develops into a clone of its parent. Example: Sea star, Japanese Knotwood. 4. Vegetative Reproduction Occurs when special cells, usually in plant stems and plant roots, divide repeatedly to form structures that will eventually develop into a plant identical to the parent Examples: Tubers such as potatoes, tulips or runners such as strawberries, blackberries and raspberries. Vegetative Reproduction… Potato Strawberries 5. Spore Formation Single-celled reproductive cells that grows into a new individual by mitosis. Example: Mold Advantages/Disadvantages of Asexual Reproduction Advantages Disadvantages Large number of offspring from one parent Offspring are genetic clones. Mutations of genes could wipe out all from disease Large numbers can form and outcompete other organisms for food Large numbers of organisms can be too close together (physically) and compete for food Large number of organisms mean that species has better ability to survive better If conditions are extreme then entire species can be wiped out Energy is not required to find a mate Core Lab Determining the Best Conditions for Yeast Production