Instruction sheet
IB BIOLOGY
Components assessed: Dcp; ce
To examine the relationship between surface area to volume ratio and rate of
diffusion
Apparatus and Materials
● Petri dish containing pink agar
● A scalpel and a spatula
● Graph paper
● Dilute Hydrochloric acid (0.05 M)
● A stopwatch
● Boiling Tubes /beakers
● A test-tube rack
● pair of gloves
● A white tile/paper
Procedure
1.
You are provided with petri dish(s) of pink agar. Use a scalpel to cut it into
small pieces with different dimensions for example 1cmX1cmX1cm
Choose an appropriate range of dimensions
2.
Immerse each agar piece separately in dilute HCl in a boiling tube. Place
the tube in the test tube rack.
3.
Observe as the acid diffuses into the block turning it colorless.
Examine them regularly and record the time taken for each block to turn
completely white. Note any relevant associated qualitative observations.
4.
Try to expose the agar pieces to the air as little as possible to minimize
any reaction that could interfere with your observations.
5.
Carry out at least 5 repeats for each dimension you have chosen .
Some dimensions(in cm )which you may choose:
SA
volume
Sa:V
1x1X1
6
1
6:1
1X1x0.5
4
0.5
8:1
0.5X0.5X1
2.5
0.25
10:1
0.5x0.5X0.5
1.5
0.125
12:1