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

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)

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&sectioncode=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