Cell Division

Importance Limitations

Brainstorm

What do humans mostly use cell division for?

What do bacteria mainly use cell division for?

Name some multicellular organisms that use cell division for the same purpose as bacteria.

Why do cells divide?

1. Reproduction2. Growth3. Repair

1. Reproduction: Definitions Reproduction: production of an offspring

from a parent cell or a combination of parent cells

Asexual reproduction: one parent, offspring are identical genetic copies uses the process of cell division (mitosis)

Sexual reproduction: two parental cells containing half the genetic

information (gamete: e.g. sperm & egg) join to form an offspring new cell having a whole set of genetic information (zygote)

this type of reproduction is NOT considered cell division (mitosis) but rather meiosis

1. Cell Division for Reproduction Asexual reproduction uses cell

division (mitosis) to produce offspring

Examples of organisms that can reproduce asexually: Most single celled organisms: bacteria Some multicellular organisms:

Starfish, coral etc. Plants, fungi

Types of Asexual Reproduction Binary fission Budding Fragmentation Vegetative propagation

Binary Fission: Bacteria

Animations E. coli reproducing in the gut Rod shaped bacteria dividing /

reproducing

Binary Fission: Bacteria

Occurs in single celled bacteria

Cell division in prokaryote

Daughter cells will be identical to the original parent

Binary Fission: Bacteria

Animationshttp://highered.mcgraw-hill.com/

sites/9834092339/student_view0/chapter10/animation_-_cell_division.html

(first half)

Budding: Yeast

A small offspring will grow from the parent, and will eventually break off

Fragmentation

A new organism grows from a part that breaks off of the parent

http://www.iloveshelling.com/blog/wp-content/uploads/2011/12/starfish-regrow-arms.jpg

Fragmentation: Coral

Making an artificial reef from coral fragments Videos from Baa Atoll, The Maldives

Vegetative Propagation: Strawberry runners

Plants are identical clones connected together by a runner

http://images.tutorvista.com/content/reproduction/vegetative-propagation-by-runners.jpeg

http://krishisewa.com/articles/2011/imgs/sb01.jpg

http://www.morning-earth.org/graphic-e/biosphere/PLANTIMAGE/DISPERSAL/VEGPROP/strawberryrunners.jpg

Asexual Reproduction SummaryType Description Example

Binary fission

Budding

Fragmentation

Vegetative propagation

2. Cell Division for Growth Larger multicellular organisms do not

necessarily have larger cells but they do have more cells

Why do multicellular organisms grow by producing more cells instead of just enlarging a couple of cells? Why increase quantity instead of

increasing volume? What is the advantage of more cells

over bigger cells?

A. Multifunction

More cells are needed to carryout different jobs

Cells specialize and differentiate to carryout specific functions

Examples: Muscle cells for movement, white blood cells to fight infection

B. Efficient Communication Over a cells lifespan, the size of the nucleus

grows very little while the rest of the cell continues to grow

Efficiency of communication decreases when size increases

Yellow circle: nucleusGrey circle: cytoplasm

3 Types of Communication Types of cell communication affected by

distancea. Nucleus to the rest of the cellb. Nucleus to the cell membrane (to other cells)

Yellow circle: nucleusGrey circle: cytoplasm

3 Types of Communication Cell communication affected by

surface area to cell volume ratio:c. Cell processes to the external

environment

Yellow circle: nucleusGrey circle: cytoplasm

Activity: The Cubed Cell

Assume our cell is a cubed shape Calculate the surface area and volume of the cell as

the length of each side of the cell increases by 1 cm Plot both sets of data on the same graph

Length of one side (cm)

Surface area (cm2)

Volume (cm3)

1 6 1

2 24 8

3

4

5

6

7

8

Activity: The Cubed Cell

The effect of increasing cell size on the surface area to volume ratio

0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8

Length of one side of the cube (cm)

Total Volume (cm3)

Total Surface Area (cm2)

Activity: The Cubed Cell

The effect of increasing cell size on the surface area to volume ratio

0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8

Length of one side of the cube (cm)

Volume (cm3)

Surface Area (cm2)

Activity: The Cubed Cell

What is the effect of increasing cell size on the surface area to volume ratio?

As a cell grows, the surface area to volume ratio decreases.

0

1000

2000

3000

4000

5000

6000

7000

8000

0 2 4 6 8 10 12 14 16 18 20

Length of one side of the cube (cm)

The effect of increasing cell size on the surface area to volume ratio

Volume (cm3)

Surface Area (cm2)

Activity: The Cubed Cell

Why is this change in ratio NOT beneficial for a cell?

What types of cellular processes prefer a high surface area to volume ratio?

The effect of increasing cell size on the surface area to volume ratio

0

1000

2000

3000

4000

5000

6000

7000

8000

0 2 4 6 8 10 12 14 16 18 20

Length of one side of the cube (cm)

Volume (cm3)

Surface Area (cm2)

Diffusion: the cell processes that limits cell size Diffusion: movement of substances

across a membrane from an area of high low concentration

Examples of cell usage of diffusion: Water product excretion Absorption of gases (e.g. oxygen) Absorption of chemicals and nutrients

(e.g. sugar)

B. Efficient CommunicationCommunication between

Restrictions for efficient communication

Nucleus and organelles (and other cell parts)

Distance of nucleus to rest of cell

Nucleus and other cells

Distance of nucleus to cell membrane

Cell processes to external environment

Volume of cell to amount of cell membrane

3. Repair

Normal replacement Cells have limited lifespan Cell death by apoptosis

Maintenance Cells get injured and need

to heal Cell death by necrosis

http://www.timeshighereducation.co.uk/story.asp?storyCode=198208&sectioncode=26

Repair: Normal Replacement

Cell Type Lifespan

Lining of gut

5 days

Skin 14 days

Red blood cell

120 days

Liver cell300-500

days

Bone 10 years

Neurons From birth

Each type of tissue has its own turnover time related to the workload endured by the cells

Most cells in our body are less than 10 years old

Repair: Normal Replacement Death by apoptosis:

programmed cell death regulated and controlled

Cell cycle regulates how long a cell lives

Purpose: a way of removing unwanted cells cell no longer useful to the organism

Mechanism of Apoptosis

Specific Signal

Apoptosis: regulated cell death

Repair: Maintenance

Death by Necrosis due to unexpected and accidental cell

damage/injury that cannot be repaired Causes:

Toxins Radiation lack of oxygen due to the blockage of

blood flow

Mechanism of Necrosis

Cell Damage

Summary of Repair mechanisms

Type of repair Replacement

Maintenance

Type of cell death

Definition of death

Cause

Mechanism