Content Objective: To explain why surface area to volume ratio affects cell size.

Language Objective:  Using agar cylinders as example, explain why cells are the size they are and support this statement using a graph of time .vs. SA/V ratio

Instructions - No phenolphtalein

Research Question:

To determine how the surface area to volume ratio affects the rate of diffusion of dilute hydrochloric acid through agar blocks.

Materials (per group)

Large block of universal indicator agar 

1 x 30±0.1cm ruler 

Cork borers

1 x White Tile (to cut on)

200ml dilute hydrocloric acid (0.1M)

1 x 500-1000ml beaker

Stop watch (±1s)

Cork Borers of different size

Method

1. Using different sized cork borers, Cut 5 agar cylinders on the white tile into a range of 5 different diameters. Record the diameter and cut all of the blocks to 2.5 cm.  

2. Measure the diameter of the cylinders.

3. Place the agar blocks in the watch glasses so that they are not touching.

4. Cover the agar blocks with dilute HCL.

5. Time (in seconds) how long it takes for each block to become completely pink. 

6. Record these times in seconds on the spreadsheet (LINK).

Data Processing 

7. Create a data table for all the data collected and determine the average time to fully diffuse and the standard deviation for each diameter.

8. Calculate the Surface area to volume ratio for each cylinder

9. Create a data table with SA/V ratio and the average time to diffuse with standard deviation.

10. Graph SA/V ratio vs. Time of diffusion with standard deviation as error bars.  (See here for curved lines of best fit)

11. Write an interpretation, including stats, conclusion, and evaluation for your results.

Instructions - w/phenolphthalein

Research Question:

To determine how the surface area to volume ratio affects the rate of diffusion of sodium hydroxide through agar blocks.

Materials

Large block of phenolphthalein agar 

1 x 30±0.1cm ruler 

Cork borers

1 x White Tile (to cut on)

200ml dilute sodium hydroxide (0.1M)

1 x 500-1000ml beaker

Stop watch (±1s)

Cork Borers of different size

Method

1. Using different sized cork borers, Cut 5 agar cylinders on the white tile into a range of 5 different diameters. Record the diameter and cut all of the blocks to 2.5 cm.  

2. Measure the diameter of the cylinders.

3. Place the agar blocks in the watch glasses so that they are not touching.

4. Cover the agar blocks with dilute sodium hydroxide.

5. Time (in seconds) how long it takes for each block to become completely pink. 

6. Record these times in seconds on the spreadsheet (LINK).

Data Processing 

7. Create a data table for all the data collected and determine the average time to fully diffuse and the standard deviation for each diameter.

8. Calculate the Surface area to volume ratio for each cylinder

9. Create a data table with SA/V ratio and the average time to diffuse with standard deviation.

10. Graph SA/V ratio vs. Time of diffusion with standard deviation as error bars. (best to do with Excel or LoggerPro)

11. Write an interpretation, including stats, and conclusion for your results.

Data

Resources

Analysis

This is the process of making sense of the data that will then lead into a conclusion. Evidence includes; the explanation of trends, comparisons, correlations, optima, maxima (plateau) or the correct interpretation of the results of statistical calculations. 

• If the data collected and processed does not finally lead to clear patterns or trends then the efforts to make sense of the data objectively will be rewarded. 


• When interpreting a graphical relationship be careful of the thoughtless presenting of the Excel best-fit equation as the outcome finding.

• There is more value in recognising the relationship to be linearly proportional, inversely proportional, exponentially proportional, etc. 


Conclusion 

• A statement or discussion of whether the data answers the RQ should be presented. 

• It should refer back to the RQ and be scientifically justified with comparisons made to properly referenced background material. 

•  If a hypothesis has been proposed (IT IS NOT REQUIRED) then the candidate should conclude whether the data does or does not support it. 

• Tie it back to the real world problem you discussed.

•  It is most likely that the data may go some way to supporting (that’s a good word to use!) a conclusion but will rarely be sufficient to be considered incontrovertible evidence in a school-based investigation. 

• The context needs to be relevant. It may refer to the correct scientific context presented in the background information, or accepted literature values. 

• If there is no accepted value available, the findings need to connect to the relevant scientific context to provide justification the candidate used the scientific context to show or prove that the findings are reliable. 

Resources

Analysis

This is the process of making sense of the data that will then lead into a conclusion. Evidence includes; the explanation of trends, comparisons, correlations, optima, maxima (plateau) or the correct interpretation of the results of statistical calculations.

• If the data collected and processed does not finally lead to clear patterns or trends then the efforts to make sense of the data objectively will be rewarded. 

• When interpreting a graphical relationship be careful of the thoughtless presenting of the Excel best-fit equation as the outcome finding.

• There is more value in recognising the relationship to be linearly proportional, inversely proportional, exponentially proportional, etc. 

Conclusion

• A statement or discussion of whether the data answers the RQ should be presented.

• It should refer back to the RQ and be scientifically justified with comparisons made to properly referenced background material. 

• If a hypothesis has been proposed (IT IS NOT REQUIRED) then the candidate should conclude whether the data does or does not support it. 

• Tie it back to the real world problem you discussed.

• It is most likely that the data may go some way to supporting (that’s a good word to use!) a conclusion but will rarely be sufficient to be considered incontrovertible evidence in a school-based investigation.

• The context needs to be relevant. It may refer to the correct scientific context presented in the background information, or accepted literature values.

• If there is no accepted value available, the findings need to connect to the relevant scientific context to provide justification the candidate used the scientific context to show or prove that the findings are reliable.