Liver Experiment

Review

The group worked well throughout the duration of the experiment. As a group, decisions were made quickly on who was going to undertake each task. Some of these tasks included setting up the water bath and making the hydrogen peroxide concentrations. The group thought it would be a good idea if the experiment were conducted whilst someone else collected the results and made a table. The group worked strongly to finish this practical in an efficient and appropriate manner, collecting precise results.

Photos

Results

Concentration (%) Trial One (mL) Trial Two (mL) Trial Three (mL) Average (mL) Rate (mL/min)

0%

0 0 0 0 0

1%

30 38 25 31 16

2%

68 35 68 57 29

4%

140 120 100 120 60

6%

100 102 98 100 50

8%

120 126 100 115 58

The liver was stored in the fridge and taken out prior to the commencement of the investigation. Therefore, the outside of the liver would be warmer than the inside of the liver, because the outer extremities of the liver sample would heat to room temperature at a faster rate than the interior. Hence, as the liver cubes were cut from both the outside and the inside of the liver, they would not be of equal temperature. Temperature readily affects the rate of decomposition of hydrogen peroxide by catalase. At low temperatures the catalase and the hydrogen peroxide molecules have less energy, thus, there are fewer successful collisions between the molecules, resulting in a decreased rate of decomposition of hydrogen peroxide, hence, reducing the volume of foam produced. Therefore, cubes cut from tissue nearer the centre of the organ would produce less foam, as the rate of decomposition of hydrogen peroxide are lower due to the lower liver cube temperature. Conversely, cubes cut from tissue closer to the outside of the organ would produce more foam as the rate of decomposition of hydrogen peroxide is higher due to the higher liver cube temperature. The random nature of the temperature of the liver cubes would therefore be expected to contribute to random error and hence the scatter observed in the

When the liver was being cut, it moved and changed shape. For example, if the liver cube was turned on its side, it would spread out, becoming longer and thinner. This made it very difficult to precisely cut 1cm x 1cm x 1cm cubes, as the cube changed shape each time it was reorientated. This increased random error, as the change in shape would affect the surface area of the cube, thus, increasing or decreasing the rate of breakdown of hydrogen peroxide leading to variation in the volume of foam evolved.

Another major weakness was the rising of the volume of foam evolved. Due to the fast enzyme-catalysed breakdown of hydrogen peroxide into water and oxygen, the foam was constantly rising. Therefore, it was difficult to read the volume of foam evolved at exactly two minutes. This was made more difficult by the fact that the foam didn’t have a meniscus; therefore, measuring the exact volume of foam at precisely two minutes was difficult. This leads to inaccurate readings as the volume of foam had to be estimated, therefore, increasing the random error in the