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  • The Cell Cycles Mitosis and Meiosis

    Essential question:

    How do cells reproduce and why?

  • Objectives Section 10.1

    Explain why cells divide in terms of growth and cell size

  • Review - Types of Cell Division

    2 Types of cell division


    Several purposes


    One purpose

  • Review - Types of Cell Growth

    Individual Cell Size Increase

    Number of Cells Increases

  • 10.1 Why Divide?

  • 10.1 Cell Growth

    A set amount of DNA is unable to meet the needs of an ever-growing cell.

    Limits to Cell Size:

    1. DNA Overload

    What is the job of the DNA of a cell?

  • 2. Exchange of Materials

    How do substances get in and out of a cell?

    As a cell grows larger, both the surface area (the cell membrane) and the volume (the cytoplasm and organelles) grow larger, but at different rates!

    10.1 Cell Growth

  • Calculating Surface Area to Volume Ratios

    Which cat has the greatest surface area to volume ratio?

    10.1 Cell Growth

  • How do you increase surface area without decreasing overall size of the organism?

    Has the volume changed?

  • 2cm





    Surface area = 2cm x 2cm x 6sides =

    24 cm2

    Volume = 2cm x 2cm x 2cm =


    SA:V = 24:8 24/8 = 3:1

    Surface area = 8x8x6 =

    384 cm2

    Volume = 8x8x8 =


    SA:V = 384:512 384/512 = 0.75:1

    Which cell has the biggest surface area to volume ratio?

    Calculating Surface Area to Volume Ratios

  • Lets Practice Calculating Cell Size

    1cm 5 cm 10 cm 20 cm 40 cm 80 cm

  • So as organisms get bigger their surface area/volume ratio gets smaller. It becomes more difficult for them to exchange materials with their surroundings.

    If the volume of a cell becomes too big for the surface area to support, substances such as food, O2, and wastes cannot diffuse in and out fast enough.

  • Objectives Section 10.1

    Explain why cells divide in terms of growth and cell size

  • 10.1 Cell Growth Review

    1. Give 2 reasons why cells divide that are not related to growth.

    The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has in moving enough nutrients and wastes across the cell membrane.

    2. As a cell increases in size, which increases more rapidly, its surface area or its volume?

    Its volume.6:1


  • 3. Calculate the surface area, the volume, and the ratio of surfacearea to volume of an imaginary cubic cell measuring 4 cm on each side.

    3 cm

    3 cm

    3 cm

    Surface area: l x w # of sides:

    Volume: l x w x h:

    SA:V ratio:

    3 x 3 x 6 = 54 cm2

    3 x 3 x 3 = 27 cm3

    54:27 = 6:3 (or 2:1)

  • How does surface area to volume affect the physiology of organisms?

    (Lets look at a related concept!)

    Is it better to be a large animal or a small one in cold climates?

  • Organisms also exchange heat with their surroundings. Large animals have an advantage in having a small surface

    area/volume ratio: they lose less heat than small animals.

    Why do penguins huddle?

  • Which animal has the greatest surface area to volume ratio?

    The MOUSE of course!

    How might the small surface area to volume ratio help the hippo in its natural environment?

  • Chapter 10.2

    The Cell Cycle and Mitosis

  • Objectives

    Describe the main events of the cell cycle

    Explain each of the four phases of mitosis

  • Some Cell Division Terminology

    Dont panic

    Just sharpen your pencil!

  • Each of the time periods of a cells life are referred to as phases

    This is similar to the way you can breakdown your life into phases

    Certain events are associated with each phase and can be used for identification of the phase


  • Chromosomes Chromosomes are made up of DNA wound tightly

    around proteins called histones

    Histones + DNA = chromatin

    When a cell prepares for division it duplicates its DNA and condenses the chromatin into neat packages called chromosomes

  • Chromosomes

    Exist in homologous pairs One from mom

    One from dad

    Humans have 23 pairs 22 autosome pairs

    1 sex pair (these determine the sex of the organism)

  • Sister Chromatids

    During replication (S phase) a pair of sister chromatids are made for each homolog of a chromosome pair

  • Chromosomes

    Are generally represented in their duplicated form

    A single duplicated chromosome has two parts, each called a chromatid

    Each chromatid is referred to as a sister and is attached at a centromere

  • Cell Cycle

    During the cell cycle, a cell grows, prepares for division, and divides to form 2 daughter cells, each of which then begins the cycle again.

  • Cell Cycle It includes two major stages1) Interphase

    G1, S, G2

    2) M phase (nuclear and cellular division) Mitosis (division of the


    Cytokinesis (division the cell)

  • Stage 1 - Interphase In Between


    G1= cell grows

    S =chromosomes duplicate

    G2= organelles duplicate, DNA checked

  • Stage 2 Mitosis Nuclear Division

    First part of M Phase The division of the

    nucleus of somatic (body) cells during the cell cycle.

    Its divided into 4 phases. Remember Interphase

    and Cytokinesis are NOT part of Mitosis.


    The phases of the M Phase of the cell cycle do not occur in isolation

    The are a continuum starting with prophase and proceeding sequentially through metaphase, anaphase and finally telophase

    Sometimes it can be difficult to determine the phase a cell is in because it will appear to be transitioning from one phase to another

  • Prophase

    First stage of Mitosis

    Nuclear membrane breaks down

    Chromatin condenses into chromosomes

    Centrioles (animal cells only) separate and a spindle apparatus begins to form a cage like structure across the cell

  • Prophase

  • Metaphase

    Second Phase of Mitosis

    Each chromosome is connected to a spindle fiber at an area called the kinetochore on the centromere.

    the chromosomes line up in the middle of the spindle (called the metaphase plate)

  • Metaphase

  • Anaphase

    Third Phase of Mitosis

    The sister chromatids separate at the centromere into individual chromosomes and move apart to opposite ends of the cell.

    the spindle fibers shorten and pull the chromosomes to each end (aster)

  • Anaphase

  • Telophase

    Fourth and Final Stage of Mitosis

    Nuclear envelopes reform around each complete set of chromosomes

    Chromosomes unwind back into chromatin losing their distinct shape

  • Telophase

  • Final Step - Cytokinesis The last step of M phase

    The equatorial belt pinches cytoplasm in half

    Each daughter cell has an identical set of chromosomes

  • The Whole Cell Cycle Putting it all together!

  • So what is the END RESULT?

    One Parent Cell


    Two identical Daughter Cells

  • Regulating the Cycle

    Proteins called cyclin help regulate the cell cycle in eukaryotic cells.

    They respond to internal and external events. These proteins are regulators.

  • When Things Go Wrong

    Some cells begin to grow without regulation They produce a mass of cells called a tumor

    Benign tumors do not cause damage to surrounding tissues

    Malignant tumors DO cause damage to tissues and may become cancerous

    Cancer cells do not respond to the signals that regulate the growth of most cells.

    As a result, they form masses of cells called tumors that can damage surrounding tissues.

    Brief animation!

  • 11-4 Meiosis

    Cell Division for Sexual Reproduction

  • Homologous Chromosomes

    All sexually reproducing organisms inherit one set of

    chromosomes from each parent

    Each parental set contains exactly the same number of


    The corresponding chromosome from each parent is called

    a homolog

    2 homologs make a homologous pair

  • Chromosome Pair 1

    Chromosome Pair 2

    Chromosome Pair 3

  • Chromosome Number

    Diploid (2 N)

    Cells with a complete set of homologous pairs

    Haploid (N)

    Cells with one half the homologous chromosomes in a diploid cell

    Lets do a quick activity to investigate this.

  • What is Meiosis?

    A cell division cycle which reduces the number

    of chromosomes in new cells by half

    Diploid (2N) somatic (body) cells are reduced

    to haploid (N) gamete (sex) cells

    Chromosome reduction occurs by separation

    of homologous chromosomes

  • Meiotic Cell Division the Basics

    Meiosis involves 2 distinct phases

    Meiosis I