1. Sit at a new table with 75% new people
Take out mini-posters and mastery checklist

2. Grades due Friday Announcements 2B Assessment--Wed/Thur Dec 4-5
Miniposters part of grade
Flip book and 4 macromolecule videos due for Thursday mingle
Grades due Friday
Check board or weebly for office hours

3. Cell Size Limitations
Why are cells so small?

4. Most cells are between 2µm and 200µm
A micrometer is 1 millionth of a meter!
Too small to be seen with naked eye

5. Why is General Sherman millions of cells and not one big cell?

6. Limits Diffusion limits cell size
Movement from higher concentration to lower concentration
Larger the distance, slower the diffusion rate
A cell 20 cm would require months for nutrients to get to the center

7. DNA limits cell size
larger cells need more DNA. Needs more of everything
Most cells have just one nucleus

8. Surface area to volume ratio limits size

9. Volume increase more rapidly than surface area.
Cell size doubles, 8x as much volume, but only 4x as much surface area

10. So, if too big is a problem, what’s the solution
So, if too big is a problem, what’s the solution? Cells divide before they become too big
Process of cell division is called mitosis

11. Why do cells divide?
Replacement
Repair
Growth

12. Measure the rate of diffusion for 3 different cell sizes
Drop them carefully in HCl and watch the rate of diffusion
Need to calculate SA/V for 3 cells and rate of diffusion
Take ruler, calculator, timer into lab

13. Roles in Lab Beakers of HCl (pour 30ml carefully) Jello block cutters
Timer + Beaker washer
Measurer + Data Collector

14. Contest Design a cell with the highest surface to volume ratio
Include:
Calculations for your design
Drawing of your new cell with the dimensions indicated
How will you measure if this cell is faster than the 1 cm x 1 cm x 1 cm cell? In other words - what data are you going to collect?

15. To get a stamp on 2B
Change mastery checklist—last stamp should be cell size lab
Answer questions
Show all calculation from cells
Show contest calculations and drawing on back