1. Agar cubes Lab

2. Cell size
Cells are limited in size – you can’t see them without a microscope for good reason!
As a cell gets larger and larger (as it eats more and more), it takes longer and longer to get food/waste in and out

3. Cell size
Cell becomes “bloated”, can’t compete as well with smaller, quicker cells
Needs to divide to become competitive again
Mitosis!

4. Surface Area/Volume
Surface area – the total area on the outside of an object
Volume – the amount of space taken up by an object
The ratio between the two limits the sizes of cells!

5. 3cm cube Surface Area (S.A.) = Volume Ratio S.A.:Volume:
Area of all sides, added together
3cm cube
3 x 3 = 9cm2
6 sides to a cube
Total surface area = 54cm2
Volume
Length x height x width
Same cube
3 x 3 x 3
Total volume = 27cm3
Ratio S.A.:Volume:
Surface Area / volume
54:27 or 2:1

6. 2cm cube 2cm cube Surface area: Volume: Ratio S.A.:Volume: 3:1
2 x 2 x 6
24cm2
Volume:
2 x 2 x 2
8cm3
Ratio S.A.:Volume:
24:8
3:1

7. 1cm cube 6:1 Do calculations on your own Surface Area: Volume:
1x1x6
6cm2
Volume:
1x1x1
1cm3
Ratio S.A.:Volume:
6:1

8. Example
0.1cm cube
Surface area = 0.06cm2
Volume = 0.001cm3
SA/V = 60:1
0.01cm cube
Surface area = cm2
Volume = cm3
SA/V = 600:1
The smaller the cell, the higher the ratio is! This is why cells divide to stay small!

9. Today’s Lab Cutting cubes of agar into 1cm, 2cm, and 3cm cubes
Phenolphthalein in the agar cubes is an indicator
Turns pink in base
Turns clear in acid

10. Today’s Lab We will be soaking the cubes in vinegar (acetic acid)
Look to see how far it penetrates into larger vs. smaller cubes
Which do you think will diffuse faster?
Why?
This is similar to how long it takes food/waste to diffuse in/out of larger vs. smaller cells

11. Instructions Wear goggles AND aprons today
Cut your agar block down the middle, and split between two groups
Carefully cut out your 1cm, 2cm, and 3cm cubes from your agar
Remember – cubes have the same height, length, and width!
Be sure to accurately measure the length of the sides, so you can do proper calculations
Place the three cubes in the 250ml beakers
Cover with vinegar and wait until

12. Instructions
After 10 minutes has expired, pull cubes out of vinegar and gently rinse off
Measure the remaining Nuclear Pink Agar
Calculate the rate of diffusion
Final Volume of Nuclear Pink Agar – Then Trash
Clean up & answer analysis questions
Return the following to Prep Table:
Vinegar
Ruler
Plastic Knife,
Milk Carton (Clean, Dry)