Science 9- Mr. Klasz
Asexual reproduction requires only one parent. The offspring produced are identical to the parent. Asexual reproduction occurs in our somatic cells. This means all of our cells except for sperm cells in males and egg cells in females.
For three reasons: Growth We grow from one initial cell to an adult. Repair When we injure ourselves, our cells must reproduce asexually to replace this. Replacement Our cells are constantly being replaced. Most of our cells have a very short life span.
Our cells don t live for ever! Some are programmed to die (PCD-Programmed Cell Death). Some cells die when they are damaged and cannot function. Some cells die when they don t receive enough food or oxygen. These cells need to be replaced for our bodies to continue to function! 3 billion cells die every minute in your body!!! Our cells have varying life spans.
Asexual Reproduction/Mitosis! As we just stated-our cells are continually dying. As we age, they are either not replaced, or are replaced more slowly. When our cells stop replacing themselves at a fast pace, our skin wrinkles, our bones become weak, and we our immune system is weakened.
Our cells are programmed to die when something goes wrong, but cancerous cells cannot do this. When cells divide at an uncontrollably fast rate, cancer is created. The cancerous cells spread quickly, and starve the good cells of oxygen and food. The risk of cancer is increased by tobacco, radioactivity, UV radiation, etc
The first cell of a new organism is called the zygote. It is created by the fusion of the sperm cell and the egg cell. This cell will divide into two, these two cells will each divide into two more (four total cells) and so on to create the new organism. Each of these cells must contain identical genetic material.
If cells simply divided into two, there would be only a fraction of the original nucleus (and therefore original DNA) in each cell. To ensure that each cell has an entire set of chromosomes, each of our cells goes through what is called The Cell Cycle each time they divide.
The Cell cycle allows the cell time to under go the process of cell division (mitosis + cytokinesis), and replicate its DNA The majority of a cells life is spent in the interphase and growth portions of its cycle.
The cells of many plants and animals undergo the cell cycle explained on the previous slide. This includes all human cells except for our sex cells.
Interphase (preparing to begin mitosis) Mitosis (There are 4 phases) Prophase Metaphase Anaphase Telophase Cytokinesis (occurs after mitosis)
Interphase Prophase Metaphase Anaphase Telophase Cytokinesis http://www.cellsalive.com/mitosis.htm
Genetic material, called DNA, is found on the chromosomes located in the nucleus of a cell. The genetic material that makes up chromosomes is called chromatid. When the chromatid is duplicated, the two identical sister chromatids are attached in the middle by a centromere.
The period between cell divisions is called interphase. During this period, the cell grows and the genetic material (called chromatid) duplicates The duplicated sister chromatids attach in the middle by a centromere to create a double stranded chromosome. This process ensures that the same genetic information is passed on to each of the two new daughter cells.
During prophase: The double-stranded chromosomes condense (shorten and thicken) The nuclear membrane (the membrane surrounding the nucleus) starts to dissolve. The centrioles move to opposite poles of the cell The spindle fibers begin to form from the centrioles Spindle fibers attach to opposite ends of the centromeres
During metaphase: The spindle fibers tug on opposite sides of the centromere This tugging action causes the double-stranded chromosomes to form a straight line at the equator of the cell. This equator is called the metaphase plate.
During Anaphase The spindle fibers contract and shorten. This causes the centromere to split in two. One sister chromatid moves towards each pole of the cell. If this process is successful each daughter cell will have a complete set of identical genetic information.
During Telophase: The spindle fibers continue to shorten, pulling the sister chromatids all the way to opposite poles. The spindle fibers begin to disappear The nuclear membranes form around each set of single-stranded chromosomes. The chromosomes begin to uncoil into thin strands of chromatid. In animal cells, the cleavage furrow begins to form to divide the two new cells.
Cytokinesis happens after mitosis. During cytokinesis: Animal cells: The cell membrane pinches off near the middle of the cell, dividing the cytoplasm into two new cells. Plant cells: A cell plate develops across the centre of the cells, forming a new cell wall and two new cells.
Interphase Prophase Metaphase Anaphase IPMATC Telophase Cytokinesis I Play Music At The Concert