1. November 17, 2010

2. Warmup
Write a sentence and draw a picture to describe the relationship between each set of words:
Chromatin and chromosomes
Chromatids and chromosomes
Centromere, chromosome, chromatids
Centriole, spindle and chromosomes
Daughter cells and sister chromatids

3. Cell Growth Notes

4. Limits to cell growth 1. DNA “overload”
There are two things that limit a cell’s growth
1. DNA “overload”
All the information needed to control a cell is found in the cell’s DNA (in nucleus)
Small cells- Info in the DNA is enough
Large cells- the DNA would not be able to tell the cell what to do
It would not have enough information for the cell

5. Limits to cell growth cont…
2. Exchange of materials
Many things must enter and leave through the cell membrane
i.e. water, oxygen, CO2, food, waste
Why does the surface area matter?
The rate of this exchange depends on the surface area of the cell membrane
Why does volume matter?
HOWEVER, the rate at which products are used depends on the cell’s volume
So, the comparison of surface area to volume is critical for a cell

6. Limits to cell growth cont…
Ratio of surface area to volume
Divide surface area by volume
Example #1: What is the ratio of surface area to volume of a cubic cell with a length of 1 cm?
Surface area is 1 x 1 x 6 = 6 cm2
Volume is 1 x 1 x1 = 1 cm3
6/1 = 6:1 ratio

7. Limits to cell growth cont…
Example #2: What is the ratio of surface area to volume of a cubic cell with a length of 3 cm?
Surface area is 3 x 3 x 6 = 54 cm2
Volume is 3 x 3 x 3 = 27 cm3
54/27 = 2:1 ratio
Note: the volume goes up much more than the surface area!!!
So even if the surface area increase a little the volume goes up a lot!!! This is trouble for cells!

8. (length x width x height) Ratio of Surface Area to Volume
1. Look at the chart below, which cell has the most surface area? Which has the most surface area compared to volume?
2. Compare the drawings. How much longer do you think it would take to get from the cell membrane to the center of the big cell than from the cell membrane to the center of the smaller cell?
3. What is the advantage of cells being small?
Cell A
Cell B
Cell C
Cell Size
Surface Area
Volume
(length x width x height)
Ratio of Surface Area to Volume

9. Limits to cell growth cont…
Cells combat these issues of too much volume for surface area and too little DNA by dividing!!!
Each cell can divide and form two new cells called daughter cells
Before each cell divides the DNA replicates (makes a copy of itself)
It also means each cell gets all of its own DNA and enough surface area

10. Homework!!!
Cell Growth and Division WS