Cells & Cell Division
An informative presentation by your wacky science teacher!
LG4: Explain basic principles of HEREDITY, including CELL
DIVISION (MITOSIS & MEIOSIS).
A Question…..What do you,
an ant,
and an oak tree
have in common
(talk to a partner)?
An Answer….
Yes, you are all living things…but more
importantly
You are all made of trillions of cells!
AND
you all started out as a single cell!
Cell Theory
In the 1830’s
Theodor Schwann & Matthias Schleiden
proposed “Cell Theory”
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.How do you become a multicellular organism if
you started out as just ONE cell (talk to a
partner)?
Cell
Division…
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?
Zygote
How Many?
You would
have 64
cells!
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?
Consider….
What are the purposes of cell division?
Growth/Regrowth
Repair
Reproduction
(Hint: This is important!)
GRR!
Growth
How tall were you when you were 5?
How tall were you last year?
How tall are you now?
Did your cells get bigger?
Discuss with a neighbor what happened
Growth
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?
Regrowth
When an organism is fully grown, some cells die off and need to be replaced.
Regrowth
• 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 need to last a
very long time!
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…….
Specialization
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.
During development, cells become
specialized to perform particular functions.
Name specialized cells in the human body
In Other Words….
Cells get instructions from DNA about
what type of cell it will become and
what will be its function!
Cell TypesSome cells might
become layered skin cells, while
others might become long, thin
nerve cells. Nerve Cells
Cheek Cells
Bone CellsRed Blood Cells
One purpose of cell division
Growth/Regrowth
Next reason…
Repair
Have you gotten a
paper cut recently?
Have you broken a
bone in your arm
or leg?
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.
Repair
Next reason…
One purpose of cell division
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)
Summary…
Cells are the main
components of all living
things
The purpose for cell
division:
Regrowth
Repair
Reproduction
Cell Cycle
Mitosis in Words
The Cell Cycle
Cell grows, makes a copy of DNA.
(90% of cell’s life is spent here!)
Chromosomes and spindle
fibers form; nuclear envelope
breaks down.
Chromosomes line up
across the center and
attach to a spindle fiber.
Centromeres split;
chromatids separate and
move to opposite ends.
Chromosomes stretch out;
new nuclear envelope forms
around chromosomes.
Cell membrane pinches in two; each
daughter cell has same number of
identical chromosomes.
Interphase
ProphaseCytokinesis
Telophase
Anaphase
Metaphase
Length of the Cell Cycle
Mitosis
One More Look at Mitosis
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.
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)
The difference between
Mitosis and Meiosis
Mi”T”osis
(“T” is for TWIN!)
Meiosis
(“MY-OH-MY! SEX CELLS!)
•One division of the
nucleus = 2 cells
•Used for growth and repair
•Creates exact “T”win 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
•Cancer is Uncontrolled
Mitosis:
Mitosis must be controlled,
otherwise growth will occur
without limit (cancer)
•Mutations in control
proteins can cause cancer
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?
Cancer
cells are
held
together.
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 organism’s trait, or phenotype,
may be different from what it normally would have
been.
Results of Mutations
If a mutation occurs in a SEX CELL, the
mutation can be passed on to an offspring
and affect the offspring’s phenotype.
If a mutation occurs in a BODY CELL, the
mutation will not be passed on to the
organism’s offspring.
Effects of mutations
Introduce change in an organism (genetic
variation)
Can be harmful (reduces the organism’s chance for
survival and reproduction)
Can be helpful (improve an organism’s chance of survival and
reproduction)
Antibiotic resistance in bacteria
Can be neither harmful nor helpful
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
Don’t forget to thank a science teacher today!