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!