1. Questioning and think-pair-share discussion
2. Why do cells divide?3. Introduction to cell cycle4. Animation5. Homework: “Cell cycle on the Internet”
handout
What is a cell?the structural and functional units of all living organisms.
Unicellular organismsingle-celled organism (ex. Bacteria)
Multicellular organismany organism made up of more than one cell (ex. Human)
Humans start out as one fertilized egg (a single cell). How does it grow into an organism with trillions of cells?
Why do you think it is important for cells to divide? and why?
1. Reproduction2. Growth3. Repair
At the end of lesson, you will understand that:
All cells divide so that the organism can reproduce, grow, and repair itself
Reproduction: production of offspring from a parent cell or a combination of parent cells
Single cellular organisms use cell division as a means of reproducing Bacteria
Some multicellular organisms also use cell division to produce offsprings: Starfish, coral etc. Plants, fungi
Asexual reproduction: one parent, offspring will have identical genetic copies
Sexual reproduction: two parental cells containing half the genetic information (gamete) join to form an offspring new cell having a whole set of genetic information (zygote) Human gamete: sperm and egg
Binary fission – daughter cells are the same size (e.g. bacteria)
Budding – the bud is smaller than the parent (e.g. yeast)
Fragmentation – a small part grows into a whole organism (e.g. starfish and coral)
Vegetative propagation – plant puts out shoots or roots that grow into identical new plants (e.g. strawberry plant)
Occurs in single celled bacteria
Cell division in prokaryote
Daughter cells will be identical to the original parent
Animationshttp://highered.mcgraw-hill.com/sites
/9834092339/student_view0/chapter10/animation_-_cell_division.html
(first half)
Occurs in single celled yeast
A small offspring will grow from the parent, and will eventually breaks off
A new organism grows from a part that breaks off of the parent
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
Why do multicellular organisms grow by producing more cells instead of just enlarging a couple of cells? Why increase quantity instead of
increasing volume? Why more cells instead of bigger cells?
Larger multicellular organisms do not necessarily have larger cells but they do have more cells More cells are needed to carryout different
jobs Cells specialize and differentiate to carryout
specific functions▪ Ex. Muscle cells for movement, white blood
cells to fight infection…
Over a cells lifespan, the size of the nucleus grows very little while the rest of the cell continues to grow
Yellow circle: nucleus Grey circle: cytoplasm
Over a cells lifespan, the size of the nucleus grows very little while the rest of the cell continues to grow
Cell reaches a maximum size due to limitations in communication when the cell gets too big 3 types of communication is affected
Communication distance from nucleus1. Nucleus to the rest of the cell (to organelles)2. Nucleus to the cell membrane (to other cells)
Yellow circle: nucleus Grey circle: cytoplasm
Communication 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
Surface area to cell volume ratio
Yellow circle: nucleus Grey circle: cytoplasm
Surface area to cell volume ratiohttp://plaza.ufl.edu/alallen/pgl/modules/rio/stingarees/module/why.html
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 1 12 24 8345678
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)
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)
What is the effect of increasing cell size on the surface area to volume ratio?
The effect of increasing cell size on the surface area to volume ratio
0
1000
2000
3000
4000
5000
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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)
Communication 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
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: 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)
Osmosis: movement of water across a membrane from an area of high water (low solute) low water (high solute) concentration Solute: a substance dissolved in another substance;
the component of a solution present in the lesser amount
As a cell grows, the surface area to volume ratio decreases. Limitations of communication
▪ Between nucleus (control center) and organelles
▪ Between nucleus and other cells▪ Between cell and external environment
Maintenance: healing due to injuryNormal replacement: due to cell
lifespan 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
http://www.timeshighereducation.co.uk/story.asp?storyCode=198208§ioncode=26
Cell Type LifespanLining of gut 5 days
Skin 14 daysRed blood cell 120 days
Liver cell 300-500 daysBone 10 years
Neurons From birth
The cell cycle regulates how long a cell lives
Sometimes cells die because they have suffered injury or damage that cannot be repaired
http://www.youtube.com/watch?v=rgLJrvoX_qo&feature=related
InterphaseMitosis
Scientists have identified a repeating cycle of events in the life of a cell
This cycle of events is called the cell cycle
Every hour, about one billion (109) cells die and one billion cells are made in your body. Part of the cell cycle includes making new cells in a process called cell division.
The cell cycle has four phases: G1 Phase S Phase G2 Phase M PhaseInterphase
The cell spends about 90% of its time in interphase
Composed of 3 phases: G1, S, G2
Often called the “resting” phase but cell is not at rest
Cell is not dividing Cell is active:
taking in nutrients Growing conducting other
normal cell functions
http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/mitosis/images/interphase1_pc.jpg
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