JUTBMMBCPVUVOEFSTUBOEJOHBTZPVHP

Exchange Surfaces

To be able to explain, in terms of surface-area-to-volume-ratio, why multicellular organisms need specialised exchange

surfaces and single-celled organisms do not

13 Apr 2023

Exchange surfaces

Villi in the small

intestine

Exchange surfaces

Root hair cells in plants

To show the effect of surface-area-to-volume ratio on the diffusion rate of hydrochloric acid

1. Cut the agar into five different-sized cubes (from 2  mm to 10  mm) using a sharp razor, a clear ruler or callipers and a white tile.

2. Using the razor blade to lift the agar blocks, place each block into a test tube or beaker and label clearly with the size of the block.

3. Using a syringe, immerse the blocks in 2  M HCl acid by covering each block with 2  cm3 of the acid.

4. Immediately start the stopwatch and time how long the pink colour takes to disappear and for each block to turn completely colourless.

5. Record the results in a suitable table.6. Draw a suitable graph to show the effect SA:V ratio has on the

rate of diffusion.

Questions

1. Identify at least three key factors you controlled in this experiment.

2. What additional procedures could you carry out to make these results more reliable and more accurate?

3. Explain the effect of surface-area-to-volume ratio on the rate of diffusion and how this is important in living organisms using your graph and your scientific knowledge.

4. What are the limitations of this experiment when compared with living organisms?

Remember to keep small dogs warm