Cell DivisionChapter 3.1

Do Now• What happens when you get cut? • Explain in your own words what

happens when you are cut and the healing process.

Cell division occurs in all organisms– Unicellular organisms (ex: bacteria)• Binary fission

– Multicellular organisms (ex: US!)• Mitosis

Cells needs a high surface area to volume ratio

1. All organisms start as a single cell

a) Growth- limited by surface area (needs high ratio of surface area to volume)

b) High SA allows nutrients in & waste out

Why do we need cell division?• It is involved in many functions!

1. Growth – get bigger

2. Development – change

3. Repair – fix damaged or old cells

4. Reproduction – make new cells

DNA – deoxyriobonucleic acid• A chemical that contains information

for an organism’s growth and functions.

• Double helix like a twisted ladder

Chromosomes• In Eukaryotic cells, DNA is found in

the nucleus• DNA is wrapped around proteins like

thread around a spool, compacted into structures called chromosomes.

We have 46 total chromosomes= 23 pairs

Question• Even when you are done growing and

development appears to stop, is cell division still occurring?

Growth• In general, large organisms do not

have larger cells than smaller organisms.

• Simply, they just have more cells.• As an adult, you have about 100

trillion cells!

Development

• During development, cells become specialized to perform particular functions.

• These cells may take on shapes or structures that help them perform their functions.

Some become skin cells, nerve cells, etc. These cells have the same genetic material

Repair 78• The body repairs body injuries through cell

division. Ex: cut on skin or broken leg• As cells age and die, they need to be replaced.

• We are made up of 200 different types of cells• Every minute, you lose 40,000 skin cells!• Brain cells live long and do not divide often

• Surface area to volume• http://www.brown.edu/Courses/BI0020_Miller/

week/10/web-1/4-2-2007_10-20-26/Chapter_41/Present/Animations/41_A01/41_A01s.html

• Multicellular division• http://www.youtube.com/watch?v=AhgRhXl7

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• Unicellular division:• http://www.youtube.com/watch?v=J6akNYlke

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