why do cells divide? 10-1. its all about size why do cells divide? (instead of just getting bigger)...
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WHY DO CELLS DIVIDE?WHY DO CELLS DIVIDE?
10-110-1
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WHY DO CELLS DIVIDE?WHY DO CELLS DIVIDE?
IT’S ALL ABOUT SIZEIT’S ALL ABOUT SIZE
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WHY DO CELLS DIVIDE?WHY DO CELLS DIVIDE?(instead of just getting bigger)(instead of just getting bigger)
1. Diffusion
2. DNA
3. Surface area-to-volume ratio
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DiffusionDiffusion
• Cells need: – food and oxygen– to eliminate wastes– to move all materials through cytoplasm
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DiffusionDiffusion
• Typical cell has a diameter of 20 µm– takes a fraction of a second for materials to
move from cell membrane to the center of the cell
• If it had 20 cm diameter– would take months to move materials same
distance• The cell would die from starvation or poisoning
from wastes before it got that big
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DNADNA
• Cell needs:– to respond to changing conditions rapidly– to produce large amounts of proteins and
enzymes
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DNADNA
• DNA directs the production of proteins and enzymes
– DNA makes an RNA copy– RNA leaves the nucleus and travels to a
ribosome– RNA directs protein production at the
ribosome
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DNADNA
• If there is not enough DNA to control the cell the metabolism will slow and the cell will die
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WHY DO CELLS DIVIDE?WHY DO CELLS DIVIDE?(instead of just getting bigger)(instead of just getting bigger)
2. DNA
Larger cell = Greater metabolism
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DNADNA
Larger cell = Greater metabolism
Greater metabolism = More DNA needed to direct metabolism
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Surface area-to-volume ratio
• As size of a cell increases, volume increases at a much greater rate than does surface area
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Surface area-to-volume ratio
• Cell needs:– materials for processes
• obtains materials through its cell membrane
– larger organisms (or cells) need more “stuff”• more and more materials as its volume increases
– surface area for absorbing required materials
(not enough surface area to supply the needs for larger cells)
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Surface area-to-volume ratio
• Example:
Surface area of a cube = area of 1 side x 6
1 inch Area of 1 side = length x width= 1 in x 1 in
Surface area = 1 in2 x 6= 6 in2
= 1 in2
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Surface area-to-volume ratio
• Example:
Volume of a cube = length x width x height
1 inch = 1 in x 1 in x 1 in
= 1 in3
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Surface area-to-volume ratio
• Example:
Surface area : Volume ratio = 6 : 1
1 inch
Surface area = 6 in 2
Volume = 1 in3
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Surface area-to-volume ratio
• Example:
Surface area of a cube = area of 1 side x 6
4 inches
Area of 1 side = length x width= 4 in x 4 in
Surface area = 16 in2 x 6= 96 in2
= 16 in2
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Surface area-to-volume ratio
• Example:
Volume of a cube = length x width x height
= 4 in x 4 in x 4 in
= 64 in34 inches
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Surface area-to-volume ratio
• Example:
Surface area : Volume ratio = 96 : 64
Surface area = 96 in 2
Volume = 64 in3
= 3 : 2
4 inches
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Surface area-to-volume ratio
• Example:
Surface area : Volume ratio = 3 : 2
4 inches
Surface area : Volume ratio = 6 : 1
1 inch