why do cells divide? 10-1. its all about size why do cells divide? (instead of just getting bigger)...
TRANSCRIPT
WHY DO CELLS DIVIDE?WHY DO CELLS DIVIDE?
10-110-1
WHY DO CELLS DIVIDE?WHY DO CELLS DIVIDE?
IT’S ALL ABOUT SIZEIT’S ALL ABOUT SIZE
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
DiffusionDiffusion
• Cells need: – food and oxygen– to eliminate wastes– to move all materials through cytoplasm
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
DNADNA
• Cell needs:– to respond to changing conditions rapidly– to produce large amounts of proteins and
enzymes
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
DNADNA
• If there is not enough DNA to control the cell the metabolism will slow and the cell will die
WHY DO CELLS DIVIDE?WHY DO CELLS DIVIDE?(instead of just getting bigger)(instead of just getting bigger)
2. DNA
Larger cell = Greater metabolism
DNADNA
Larger cell = Greater metabolism
Greater metabolism = More DNA needed to direct metabolism
Surface area-to-volume ratio
• As size of a cell increases, volume increases at a much greater rate than does surface area
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)
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
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
Surface area-to-volume ratio
• Example:
Surface area : Volume ratio = 6 : 1
1 inch
Surface area = 6 in 2
Volume = 1 in3
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
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
Surface area-to-volume ratio
• Example:
Surface area : Volume ratio = 96 : 64
Surface area = 96 in 2
Volume = 64 in3
= 3 : 2
4 inches
Surface area-to-volume ratio
• Example:
Surface area : Volume ratio = 3 : 2
4 inches
Surface area : Volume ratio = 6 : 1
1 inch