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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
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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
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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)
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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
Cell Cycle � 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
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Cell Cycle � 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
Cell Cycle � Mitosis
� There are 4 phases within the mitosis � Prophase � Metaphase � Anaphase � Telophase
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Cell Cycle � 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
Cell Cycle � Metaphase
� Chromosomes line up along the equator of the cell
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Cell cycle � Anaphase
� Spinal fibers pull apart chromosome at the centromere
Cell Cycle � 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
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Cell Cycle � 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
Cell Cycle � Prophase I
� Same processes occur as in mitosis � Chromosomes are formed and the nuclear
envelope dissolves � The difference is that 2 chromosomes pair
up.
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Cell Cycle � Metaphase I
� Instead of each chromosome lining up in the middle, the pairs line up
Cell Cycle � Anaphase I
� The pairs of chromosomes are pulled apart
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Cell Cycle � 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
Cell Cycle � 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?
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