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Transcript
Aim: Why do cells need to divide? Compare the size of these organisms Vs. Vs. Do these organisms have different size cells? No, the cells of a large organism are the same size of a small organism. How do organisms get so big? Increase number of Cells Why do cells divide rather than grow in size? XX XX XX XX XX XX XX XX + XX XX 1. DNA “Overload” DNA Library Small Town City The larger the cell, the greater the demands on the DNA library. Eventually, the cell’s DNA would no longer be able to serve the increasing needs of the growing cell. 2. Exchange of Materials Depends on: • Surface Area of Cell • Volume of Cell What part of the cell is responsible for the exchange of materials in and out of the cell? Cell Membrane The rate at which particles are able to move across the cell membrane depends on the SURFACE AREA of the cell. Surface area Several small particles have a larger surface area than ONE large particle. ? SA Rate of Exchange A)The greater amount of the cell surface exposed to the environment, the more material that can move in or out. Compare: Surface Area to Volume B)Less VOLUME in a cell allows materials to be transported through out the cell more easily. C)Cells with a greater surface area to volume ratio is more effective for the cell to exchange material in and out of the cell. What is Cell Division? The process by which a cell divides into 2 new daughter cells. What happens to the chromosomes before a cell divides? The chromosomes Size? need to be replicated before a cell divides. Why is important to copy (replicate) all the DNA in a cell before it divides? Chromosomes What are chromosomes made up of? DNA and Chromosome Protein Centromere The chromosomes are replicated. Forming two Chromatids chromatids. Replication 2 Chromatids Chromosome + Centromere When do cells divide? Repair Organism Growth What tissues in our body need to undergo a lot of cell division? Skin Why? Stomach Respiratory The cells of these tissues are Bone constantly growing or repairing themselves. Cell Cycle 1. G1 Phase- Cells increase in size and synthesize new proteins and organelles. 2. S Phase- DNA (chromosomes) are replicated. 3. G2 Phase- Many of the molecules and organelles for cell division are produced. 4. M Phase- the cell undergoes cell division. Does anyone know what the “M” stands for? Mitosis Chromosomes Mitosis Images Spindle Fibers Mitosis is the process that divides the cell’s nucleus into two, each with a complete set of genetic material from the parent cell.