Cell Division

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Cell Division

• An informative presentation by your wacky science
  teacher!
• LG4 Understand cells role in living things and
  heredity.

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A Question..

• What do you,
• an ant,
• and an oak tree have in common (talk to a
  partner)?

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An Answer.

• Yes, you are all living thingsbut more
  importantly
• You are all made of trillions of cells!
• AND
• you all started out as a single cell!

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Cell Theory

• In the 1830s
• Theodor Schwann Matthias Schleiden proposed
  Cell Theory

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Cell Theory states

1. All living things are made of cells.
2. Cells are the basic unit and function of all
   living things.
3. Living cells only come from other living cells.

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CellDivision
How do you become a multicellular organism if you
started out as just ONE cell (talk to a partner)?

• Through cell division, a single cell becomes two
  cells. Those two cells divide into four.
• Time for math how many cells would you have
  after 6 divisions?

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How Many?

• You would have 64 cells!

Thats a lot of cells!
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• Cell Division
• Cells multiply by dividing!
• Answer (talk to your neighbor)
• How does your drawing show that cell division can
  cause organisms to grow larger in size?
• Is there a limit to how large a cell can be? Why
  or why not?

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Consider.

• What are the purposes of cell division?
• Regrowth/growth
• Repair
• Reproduction
• (Hint This is important!)

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Regrowth/Growth

• How tall were you when you were 5?
• How tall were you last year?
• How tall are you now?
• Do you think Your cells got bigger?
• or
• Your cells divided to produce more cells?
• (talk with a neighbor)

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Regrowth

• While individuals grow in size, a larger organism
  has MORE CELLS than a smaller organism
• There are limits on how big a cell can get. What
  do you think is the main reason why cells only
  get to be a certain size?

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Regrowth

• Cells continue to divide to help an organism or
  part of an organism grow
• As the cell grows, more processes are needed for
  it to function, so its demand for instructions
  increases. However, the amount DNA
  (instructions) remains constant. The instructions
  will determine what type of cell it becomes.

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Specialization

• We know that cells divide in order to make bigger
  organisms. However, if cell division were the
  only process occurring in cells, all
  multicellular organisms would end up as spheres
  of identical cells.
• During development, cells become specialized to
  perform particular functions.

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In Other Words.

• Cells get instructions from DNA about what type
  of cell it will become and what will be its
  function!

COOL!
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Cell Types

• Some cells might become layered skin cells, while
  others might become long, thin nerve cells.

Cheek Cells
Nerve Cells
Red Blood Cells
Bone Cells
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One purpose of cell division

• Regrowth
• Next reason

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Repair

• Have you gotten a paper cut recently?
• Have you broken a bone in your arm or leg?

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Repair

• The body repairs injuries like these by means of
  cell division. For example.
• When your skin is cut, skin cells on either side
  of the cut make new cells to heal the wound.

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Repair

• As cells age and die, they need to be replaced.
• In the human body
• -There are about 200 different types of cells
  (remember the pictures?).
• -Every minute or so, your skin loses about 40,000
  cells!
• -In contrast, your brain cells live a very long
  time!

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One purpose of cell division

• Regrowth
• Next reason

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Reproduction

• In order for organisms to reproduce, reproduction
  (sex cells meiosis) must occur
• Reproductive cell division produces sex cells
• with ½ the genetic information from each
  parent (humans 23 from mom / 23 from dad)

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Summary

• Cells are the main components of all living
  things
• The purpose for cell division
• Regrowth
• Repair
• Reproduction

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Cell Cycle
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Mitosis in Words
Interphase
Cell grows, makes a copy of DNA. (90 of cells
life is spent here!)
Cytokinesis
Prophase
Chromosomes and spindle fibers form nuclear
envelope breaks down.
Cell membrane pinches in two each daughter cell
has same number of identical chromosomes.
Metaphase
Telophase
Chromosomes line up across the center and attach
to a spindle fiber.
Chromosomes stretch out new nuclear envelope
forms around chromosomes.
Anaphase
Centromeres split chromatids separate and move
to opposite ends.
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Length of the Cell Cycle
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Mitosis
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One More Look at Mitosis
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Meiosis (my-o-my! Sex Cells!)

• The process by which the number of chromosomes is
  reduced by half to form sex cells (sperm and egg)
• Chromosome pairs separate and are distributed to
  two different cells.
• The resulting sex cells have only half as many
  chromosomes as the other cells in the organism.

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Meiosis

• Requires two divisions of the nucleus
• Meiosis I- (Just like mitosis)
• Meiosis II- two daughter cells go through a
  second division of the nucleus. (during this
  process, there is no chromosome replication)

Meiosis II (after Meiosis I which is Mitosis)
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The difference between Mitosis and Meiosis(W.U.
- copy this slide into notes)
MiTosis (T is for TWIN!) Meiosis (MY-OH-MY! SEX CELLS!)
One division of the nucleus 2 cells Used for growth and repair Creates exact Twin of cell (diploid cells) Two divisions of the nucleus (mitosis, THEN meosis 4 sex cells cells) Used for sexual reproduction Creates cells with ½ genetic material (haploid cells) in humans, 23 chromosomes from each parent new human with 46
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• Cancer is Uncontrolled Mitosis
• Mitosis must be controlled, otherwise growth
  will occur without limit (cancer)
• Mutations in control
• proteins can cause cancer

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Cancer is a disease in which cells grow and
divide uncontrollably, damaging the parts of the
body around them. It is caused by a mutation
that causes uncontrolled mitosis.

Cancer Cells What is it?
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Cancer cells are held together.
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Mutations

• A mutation (from Latin word that means change) is
  any change in a gene or chromosome.
• Can cause a cell to produce an incorrect protein
  during protein synthesis.
• As a result, the organisms trait, or phenotype,
  may be different from what it normally would have
  been.

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Results of Mutations

• If a mutation occurs in a SEX CELL, the mutation
  can be passed on to an offspring and affect the
  offsprings phenotype.
• If a mutation occurs in a BODY CELL, the mutation
  will not be passed on to the organisms offspring.

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Effects of mutations

• Introduce change in an organism (genetic
  variation)
• Can be harmful (reduces the organisms chance for
  survival and reproduction)
• Can be helpful (improve an organisms chance of
  survival and reproduction)
• Antibiotic resistance in bacteria
• Can be neither harmful nor helpful

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Rate Yourself!

• LG4 Understand cells role in living things and
  heredity.
• Before this presentation, I was a _____ (scale
  rating 0-4)
• because I knew __________ about cells.
• now, I feel like I am a _____ (scale rating 0-4)
  because I
• learned

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Cells are Cool!
Dont forget to thank a science teacher today!