Lab+Report+4B+-+Agar+Experiment

Homeostasis
To explore the relationship between surface area to volume ratio and the rate of exchanging materials
 * Aim**

The bigger the surface area to volume ratio, the higher the rate of exchanging materials.
 * Hypothesis**

- Razor Blade - White Tile (for cutting) - Ruler - Stirrer - Stop Watch - 3 Beakers - 3 Pieces of 2 x 2 x 2 cm cube solid agar - Data logger with conductivity probe
 * Appparatus/Materials**

1. Cut one of the agar cube into 8 cubes of 1 cm in length each 2. Cut another of the agar cube into 62 cubes of 0.5cm each 3. Switch on the data logger and launch the MultiLab CE by clicking the icon on the screen 4. Plug the conductivity probe into the sensor port I/O-1 of the data logger 5. Click the set-up icon and click the 'samples' tab and choose the 'continuous' option 6. Click the 'rate' tab and choose the 'every 10 seconds' option to allow the data logger to take a reading of the conductivity every 10 seconds 7. Close the box by clicking 'ok' at the top right side of the set-up screen 8. Fill the beaker with 200 ml of tap water and place the conductivity probe in the water 9. Place the largest agar block into the beaker and click the 'run' icon 10. Stir the water with the stirring rod continuously and gently 11. Stop the experiment after two minutes using the stopwatch by pressing the red 'hand' button 12. Take note of the graph and read the highest conductivity in the period of two minutes 13. Repeat steps 9-12 for all the different sized cubes and record the results in a table
 * Methodology**


 * Data**
 * No. of Pieces of Agar Cubes || Length (cm) || Surface Area (cm2) || Volume (cm3) || Surface Area to Volume Ratio || Rate of Conductivity Change ||
 * 1 || 2 || 24 || 8 || 3:1 || 0.71 ||
 * 8 || 1 || 48 || 8 || 6:1 || 1.58 ||
 * 64 || 0.5 || 96 || 8 || 12:1 || 8.16 ||


 * Discussion Questions**

We had to measure and cut the agar block as accurately as possible because we were only given the exact amount of agar blocks. Also, we had to be careful when we were stirring the water continuously and gently as the information would be disrupted when the rod came into contact with the conductivity probe.
 * 1. What precautions did you take during this experiment?**

It can be seen that the cube with a surface area to volume ratio of 3:1 has a rate of conductivity change of 0.71, whereas the cubes with a surface area to volume ratio of 12:1 has a rate of conductivity change of 8.16, therefore it can be inferred that the rate of conductivity change is proportional (though not directly) to the surface area to volume ratio.
 * 2. What can you infer from the results above?**

The bigger the surface area of the cube, the higher the rate of diffusion.
 * 3. What do the graphs reveal to you about the rate of diffusion and the surface area of the cube?**

No.
 * 4. Combine the results to obtain class data. Is there a difference?**

I think that this is more accurate. The use of the data logger gives us more accurate quantitative results, as compared to our own observations which were relative.
 * 5. Compare this experiment with the one that you did in Lower Secondary where coloured agars were soaked in acid. Which do you think is more accurate?**

This experiment shows the relationship between the surface area of a thing (in this case, the agar cube(s)) and the rate of diffusion. This gives us a sense of how fast living organisms have to diffuse materials in/out of their cell(s) in order to sustain themselves, and what they do if the rate of diffusion is not fast enough.
 * 6. How do you relate this to the shape of simple (eg. earthworm) to complex (eg. tiger) living organisms?**

No. This is because as the cell grows bigger the surface area to volume ratio becomes smaller, therefore the surface area of the cell membrane is less efficient with a bigger volume, as compared as before.
 * 7.** **Once a cell grows to a certain size it becomes too large for the complete diffusion of needed substances throughout its cytoplasm. As a cell grows, is the surface area of the cell membrane as efficient relative to the volume of the cell?**


 * 8. Examine the agar cells below and work out the surface area to volume ratio of each cell. Which is most efficient and which is least?**