Cell Division Importance Limitations
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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§ioncode=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
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