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

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

Cell Size Limitations Why are cells so small?

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

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

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

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

Surface area to volume ratio limits size

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

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

Why do cells divide? Replacement Repair Growth

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

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

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?

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