WHEN/WHY DO CELLS DIVIDE?

BIGGER IS NOT BETTER! IMPORTANCE OF CELL MEMBRANE 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. O 2, CO 2, H 2 O O 2, CO 2, H 2 O

SURFACE AREA TO VOLUME RATIO Smaller cells have LARGER SA/V ratios! Smaller cells have LARGER SA/V ratios! Larger cells have SMALLER 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. 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. 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 doesnt 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 GROWTH –As the number of cells increases, an organism grows. –Differentiation REPAIR REPAIR –Repair damaged tissue –Mending skin, bone, blood –Replacing old cells

CELLS DIVIDE FOR: REPRODUCTION REPRODUCTION –ASEXUAL One organism produces an identical copy of itself One organism produces an identical copy of itself –SEXUAL Two organisms join genetic material to produce a unique individual Two organisms join genetic material to produce a unique individual