Transcript WHEN/WHY DO CELLS DIVIDE?

WHEN/WHY DO CELLS
DIVIDE?
BIGGER IS NOT BETTER!
• IMPORTANCE OF CELL MEMBRANE
– Controls what goes into/out of a cell
– All cells possess a cell membrane
– Cells must have a membrane surface large
enough for all necessary exchanges.
• O2, CO2, H2O
SURFACE AREA TO VOLUME RATIO
• Smaller cells have LARGER SA/V ratios!
• Larger cells have SMALLER SA/V ratios!
SURFACE AREA TO VOLUME RATIO
• As cells increase in size, the volume
increases more rapidly than does surface
area.
• This makes it more difficult for nutrients to
diffuse into the center of a cell.
– The nucleus of a cell is often a central
structure!
CARDS READY!!
Here we go…
Which cell would be more efficient
at delivering Oxygen to the
nucleus?
A) A 3 cm cell
B) A 2.5 cm cell
C) A 5 cm cell
D) Oxygen doesn’t diffuse into cells.
Which type of cells need a plasma
membrane?
A) Eukaryotic
B) Prokaryotic
C) Plant
D) All of the above
Which of the following would have
the lowest efficiency in ridding the
cell of waste?
A) A cell with a 15 SA/V ratio
B) A cell with a 3 SA/V ratio
C) A cell with a 6 SA/V ratio
D) Not enough information to answer.
Which of the following explains why
cell need to remain small in order
to be efficient?
A) Materials diffuse faster in a smaller cell
B) The nucleus does not have very far to
travel in a smaller cell.
C) Materials have a shorter distance to
travel to reach the nucleus.
D) None…the cell should remain bigger.
Moving on….
CELLS DIVIDE FOR:
• GROWTH
– As the number of cells increases, an organism
grows.
– Differentiation
• REPAIR
– Repair damaged tissue
– Mending skin, bone, blood
– Replacing old cells
CELLS DIVIDE FOR:
• REPRODUCTION
– ASEXUAL
• One organism produces an identical copy of itself
– SEXUAL
• Two organisms join genetic material to produce a
unique individual