Practical: Surface Area to Volume Ratio

PRACTICAL: SURFACE AREA TO VOLUME RATIO

OUTCOME

In this experiment you will explore the relationship between surface area to volume ratios and diffusion. This must completed in your logbooks.

BACKGROUND INFORMATION

This experiment will model cells using agar cubes. The agar cubes have been prepared with an acid-base indicator called phenolphthalein. Phenolphthalein turns pink in the presence of bases, but is colourless when exposed to acids.

The phenolphthalein agar cubes will be prepared with a basic solution of sodium hydroxide (NaOH). This experiment will model diffusion into a cell using a solution of hydrochloric acid (HCl).

EXPERIMENT: THE EFFECT OF SURFACE AREA TO VOLUME RATIO ON THE EFFICIENCY OF DIFFUSION

AIM

To investigate the effect surface area to volume ratio on the efficiency of diffusion.

HYPOTHESIS

State your hypothesis for how the surface area to volume ratio for each cube will affect the efficiency of diffusion. Make sure you justify (provide a reason) for your prediction.

VARIABLES

State the variables for this experiment. List at least three controlled variables.

Independent:

Dependent:

Controlled:

MATERIALS

Phenolphthalein indicator agar cubes (0.5cm3, 1cm3, 2cm3) - you should have three cubes in total
50 mL 0.1M sulfuric acid per beaker
1 x 250 mL beaker
Knife
White cutting tile
Ruler
Forceps
Stopwatch

METHOD

Measure the dimensions of each agar cube and cut them down to the appropriate size.
Use these measurements calculate surface area and surface area : volume in Results Table 1.
Place the agar cubes in a beaker. Cover the cubes with the sulfuric acid solution and use the stopwatch to time 5 minutes.
While waiting for the cubes to diffuse, calculate the surface area to volume ratio of each agar cube.
After 5 minutes pour the acid solution into the waste container. Rinse the agar cubes with water and then transfer them to the tile. Use a paper towel to blot them dry.
Measure the distance the acid diffused into each cube, and calculate the volume occupied by the acid.. Record your results in Results Table 2.
Use Results Table 3 to calculate the percentage of each cube diffused.
Draw a graph of cube size vs. percentage diffused on the graph paper provided.

RESULTS

Table 1: Calculate the surface area to volume ratio for each cube.

Cube Side Length (cm) Cube Volume (cm3) Cube Curface Area (cm2) SA:V ratio

2 8

1 1

0.5 0.125

0.25 0.015625

Table 2: Record the distance of diffusion into each cube.

Cube Side Length (cm) Distance of Diffusion (cm)

2

1

0.5

0.25

Table 3: Calculate the percentage volume diffused.

Cube Volume (cm3) Distance of Diffusion (cm) Volume diffused (cm3) Percentage of cube diffused (%)

8

1

0.125

0.015625

DISCUSSION

Based on your results, what can you conclude about the size of an object and its surface area to volume ratio? Why is this important?
Based on your results, what can you also conclude about cube volume and the rate of diffusion? Why does this occur?
A student stated the same shape scaled down should retain the same surface-area-to-volume ratio, the student’s reason being ‘the shapes stay the same’. Do you agree with this student? Explain your decision.
Describe one source of experimental error for this experiment and how this error affected your results.
Describe one way to improve this experiment’s procedure?

CONCLUSION

Please write a brief conclusion for your experiment.

Your conclusion should:

link back to the aim briefly re-state your results,
state limitations of the experiment and how they affect the results and,
provide suggestions for extending the investigation.

Rubric

Rubric_ Surface Area to volume ratio Practical task .docx