Cell Size. Cell Growth and Reproduction 12/3/14

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1 Cell Growth and Reproduction Cell Size Why are cells so small? Cells do not contain a circulatory system Cells receive nutrients and remove waste through diffusion Diffusion- movement of molecules from high concentration to low concentration until equilibrium is reached Diffusion occurs quickly over small distances, but very slowly over long distances The smaller the cell the quicker nutrients are spread through out the cell and waste is ejected 1

2 Cell Size The limiting factor of the cell is the surface area to volume ratio Example: a cube with dimensions of 10 x 10 x 10 What is the surface area? (l x w x 6) 600 What is the volume? (l x w x h) 1000 What is the ratio?.6 Cell Size Now imagine the cube doubled in size. 20 x 20 x 20 What is the surface area? 2400 What is the volume? 8000 What is the ratio?.3 2

3 12/3/14 Cell Division Why do cells divide? There are 3 very important reasons: Growth Repair Reproduction Growth The larger an organism is the more cells it needs to receive the nutrients and dispose of the waste Cell Division Repair Cells do not live forever, eventually each cell dies Replaced by new cells through cell division Cells are small so that when they are replaced, it doesn t disrupt the whole organism. (Car parts) 3

4 Cell Division Reproduction To create offspring to keep the species going Two types: Asexual reproduction carried out through mitosis Sexual reproduction carried out through meiosis How do cells know when to divide? Hormones from the organism signal the cell to start dividing All cells go through the first phase of growth and/or division Interphase 4

5 Interphase At this stage growth and preparation occur for cell division Three distinct stages G1- The cell grows in size and develops S- The nucleus begins to synthesize or copy DNA. Two identical copies of chromosomes are produced G2- organelles and other material are copied or made Mitosis There are 4 phases within the mitosis Prophase Metaphase Anaphase Telophase 5

6 Prophase What is the difference between chromatin, chromatid, chromosomes? Chromatin condenses to form chromosomes Nuclear envelope disappears Centrioles form spindle fibers which connect to chromatids Chromatids are single sides of the chromosome Centrioles move to opposite ends of the cell Metaphase Chromosomes line up along the equator of the cell 6

7 Cell cycle Anaphase Spinal fibers pull apart chromosome at the centromere Telophase and Cytokinesis What do you think occurs during telophase? New nuclear envelope forms around chromatid Chromatids unwind into chromatin Cytokinesis begins and pinches off new cell 7

8 Meiosis What is the purpose of this type of cell division? The formation of gametes through cell division in reproductive cells Interphase still occurs before Meiosis begins Broken down into Meiosis I and Meiosis II Meiosis I has four stages Prophase I Metaphase I Anaphase I Telophase I Prophase I Same processes occur as in mitosis Chromosomes are formed and the nuclear envelope dissolves The difference is that 2 chromosomes pair up. 8

9 Metaphase I Instead of each chromosome lining up in the middle, the pairs line up Anaphase I The pairs of chromosomes are pulled apart 9

10 Telophase I Nuclear envelope may or may not form cytokinesis occurs Pairs of chromosomes are contained within the newly formed cells At the end of cytokinesis, cell goes into Meiosis II Meiosis II The cell cycle repeats and is the same as mitosis At the end of the telophase II there are 4 daughter cells called gametes These cells only have half the number of chromosomes as other cells There are many similarities to Meiosis and Mitosis: What are some of the differences? 10

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