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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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