Method
Experiment
- Cut the agar into 5 different-sized cubes, use the razor blade to cut. The measurements should be made with vernier callipers or a clear ruler.
- Use the razor blade to place the agar block into equally sized test tubes
- Use the syringe to immerse the blocks in 3cm3 of 1M HCl
- As the HCl is added start the stopwatch
- When the block becomes colourless, immediately record the time.
- Record the results in a table and draw a graph.
- Wear safety googles, HCl is an irritant.
- Take care with the razor blade cut away from the body.
Experiment
Results
The results show that as the surface area:volume ratio the time it takes for the agar block to become colourless decreases, therefore the rate of diffusion increases. This is due to the surface area being greater compared to the volume of the agar jelly. More HCl molecules can diffuse into the jelly at the same time, therefore the HCl molecules can reach the whole of the agar in a shorter amount of time. Resulting in the agar block becoming colourless more quickly with a greater SA:Vol ratio.
Questions
Identify 3 factors controlled;
To increase the reliability the experiment should be repeated at least 3 times for each size of block. Then averaging the results and discounting any anomalies.
To increase accuracy the agar blocks should be cut more accurately, a laser cutter would be ideal as it would have much more accurate cutting than a razor blade. As you can see in the pictures of the experiment our agar blocks did not have very straight edges which would affect our surface area:volume ratio. Multiple stopwatches should be used, and each experiment should be done one at a time, so that readings for time are closer to the true value.
Explain effect of SA:Vol ratio on rate of diffusion, relate to living organisms
As the surface area:volume ratio increases rate of diffusion also increases. This allows single celled organisms that have a large SA:Vol, such as amoeba, to rely on just diffusion to provide nutrients for cell processes. Whereas multicellular organisms whom have a small SA:Vol have evolved transport systems as they cannot rely on skin surface diffusion to provide nutrients to the cells in the body quickly.
Limitations of experiment to compared to a living organism
The experiment uses a lifeless agar jelly block, which lacks a cell membrane which allows diffusion to take place in all living cells. The cell membrane is a complex mix of a phospholipid bilayer, protein carrier channels, ion channels, carbohydrates, proteins. The agar block lacks this important feature. Other than that its is a good way to show the comparison between surface area:volume ratio and rate of diffusion
Questions
Identify 3 factors controlled;
- Temperature
- Size of reciprocal HCl is in
- Concentration difference of HCl to the agar.
To increase the reliability the experiment should be repeated at least 3 times for each size of block. Then averaging the results and discounting any anomalies.
To increase accuracy the agar blocks should be cut more accurately, a laser cutter would be ideal as it would have much more accurate cutting than a razor blade. As you can see in the pictures of the experiment our agar blocks did not have very straight edges which would affect our surface area:volume ratio. Multiple stopwatches should be used, and each experiment should be done one at a time, so that readings for time are closer to the true value.
Explain effect of SA:Vol ratio on rate of diffusion, relate to living organisms
As the surface area:volume ratio increases rate of diffusion also increases. This allows single celled organisms that have a large SA:Vol, such as amoeba, to rely on just diffusion to provide nutrients for cell processes. Whereas multicellular organisms whom have a small SA:Vol have evolved transport systems as they cannot rely on skin surface diffusion to provide nutrients to the cells in the body quickly.
Limitations of experiment to compared to a living organism
The experiment uses a lifeless agar jelly block, which lacks a cell membrane which allows diffusion to take place in all living cells. The cell membrane is a complex mix of a phospholipid bilayer, protein carrier channels, ion channels, carbohydrates, proteins. The agar block lacks this important feature. Other than that its is a good way to show the comparison between surface area:volume ratio and rate of diffusion