Biology Lab Report - Movement in and out of Cells (4A)

Biology Lab Report - Movement in and out of cells (4A) Shiang Chen Ting (24) Sec 313

Introduction The aim of this experiment is to explore the factors which affect the movement of materials in and out of the cells. The dark red or purple colour of Beetroots is caused by a pigment called betalain that is found within the vacuole of the beetroot cells. The pigment remains intact within the cell if the cells are not “stressed” by the external environment. In this exploration, two factors that affect the movement of the betalain out of the beetroot cells will be explored – surface area of the beetroot and the change in the external environment.

I hypothesize that the 4ml of 50% alcohol in which the beetroot cells are submerged in would contain the most amount of pigments diffused from the beetroot cells. Osmosis, which is the net movement of water particles from a region of higher water potential to a region of lower water potential through a selectively-permeable membrane until equilibrium is reached, occurs the most for the beetroot cells which are submerged in the 4ml of 50% alcohol. This is because, the 4ml of 50% alcohol is the most concentrated solution among the 5 set-ups, hence would be the most hypertonic solution to the beetroot cells. Hence, osmosis would occur more rapidly from the beetroot cells to the solution, resulting in the 4ml of 50% alcohol containing the most amounts of pigments.

Materials and methods The apparatus needed for the experiment are as follows: o Razor blade/ scalpel o Ruler o 5 test tubes & rack o Labels o Forceps o Distilled water o 25%, 50% alcohol o Beetroot (Beta vulgaris) o White tile (for cutting) o 2 petri dish o 3 droppers (water, 25%, 50% alcohol) o Thermometer o Stop watch o 2 Beakers o Supply of hot water o Spectrophotometer (Data logger)

The methods to carry out the experiment are as follows: 1. Use a ruler and scapel to cut the cylinder of beetroot into 15 discs of 2mm each. 2. Take 3 discs of beetroot and cut them further into smaller pieces. This is one of the independent variables (amount of exposed surface area). 3. Rinse the beetroot discs and pieces until the water is colourless. This is to ensure a fair experiment, as we can know for sure that whatever pigments found in the water at the end of the experiment is a result of osmosis, and not because the pigments found on the beetroot discs when they were cut were rinsed off them. 4. Label and prepare 5 test tubes as follows: Tube Content A: 4ml of water B: 4 ml of 25% alcohol C: 4 ml of 50% alcohol D: 4 ml of hot water (900C – 1000C) E: 4ml of water This is another independent variable – the change in external environment in which the beetroot cells are submerged in. 5. Place 3 discs of beetroot in tube A – D and all the chopped beetroot in tube E using the forceps. 6. Leave the tubes to stand in your test tube rack for 15 minutes. 7. Write the prediction of what might happen in each tube. 8. Shake the tubes gently after 15 minutes (this is to ensure that the colour is uniformly spread in the test tube) and hold it against the white tile to note the colour (this is to make sure that the judgment of colour of the solution is accurate). Record your observations in a table. 9. In the interim of the 15 minutes, switch on the data logger and launch MultiLabCE by clicking the MultiLabCE icon on the screen. 10. Plug the colorimeter into sensor port I/O-1of the data logger. 11. Click the “setup” icon and click the “samples” tab. Scroll down and choose the “continuous” option. 12. Click “ok” at the top right side of the setup screen. 13. Fill a cuvette with water up to the mark. 14. Place the cuvette in the colorimeter and hold the cap close. (Make sure the sides of the cuvette are dry before inserting into the colorimeter). 15. Click the “run” icon ( ) and twist the knob at the front of the colorimeter, adjusting such that the screen registers 100%. This is to calibrate the machine by using water that allows 100% of the light to pass through. 16. Press the red “hand” button that appears in place of the “run” icon in order to stop the experiment. 17. Shake the test tubes gently after 15 minutes and hold it against the white tile to note the colour. Record your observations in a table. 18. Decant a small amount of liquid from test tube A into a cuvette and place it into the colorimeter. 19. Click the “run” icon again and record the value of light transmission once the value is relatively steady. 20. Repeat steps 18 & 19 for all the test tubes and record your results in a table. 21. Dispose of the content of the tubes after the experiment. Do not throw the beetroot into the sink.

Variables There are two independent variables in this experiment – the surface area of the beetroot cells, as well as the external environment in which they are submerged in. The dependent variables would be the colour change in the test tubes at the end of the experiment resulting from the osmosis of pigments from the beetroot cells into the solutions. As for the controlled variables, some examples would be the size of the beetroot discs (whether their measurements are uniform from A to D), the amount of solution in each set-up, the external environment in which the experiment is held, etc. Results

Tube I/O-1 (%) Colour A 88.2 Very faint red, almost transparent B 78.5 Light red C 28 Very bright red D 91.4 Very faint red E 80.3 Pale red, redder than A and D but less bright than B

Analysis of results and Discussion As seen from the table above, tube A which contains 3 discs of beetroot submerged in 4ml of water has an I/0-1 of 88.2%. Its colour when placed against a white tile is observed as very faint red, almost transparent.

Tube B, which contains 3 discs of beetroot submerged in 4ml of 25% alcohol, has an I/O-1 of 78.5%, and is observed as having a light red colour. Tube C, which contains 3 discs of beetroot submerged in 4ml of 50% alcohol, has an I/0-1 of 28% and is observed as having a very bright red colour. The reasons why the colour in tubes B and C are a more opaque shade of red might be attributed to the content of the solution. The solutions in tubes B and C are 25% alcohol and 50% alcohol respectively, so this means that the solutions are concentrated and are actually hypertonic to the beetroot discs. Hence, osmosis of pigments can occur more rapidly as the pigments travel from the region of higher water potential (beetroot cells) to the region of lower water potential (the 25% and 50% alcohol solutions), as compared to other test tubes.

Test tube D, which contains 3 discs of beetroot submerged in 4ml of hot water, has an I/O-1 of 91.4%, its colour being observed as very faint red. It is the most translucent of all the 5 set-ups. However, according to my research on the Internet, there have been several articles which state that a higher temperature would result in higher kinetic energy of molecules; hence the rate of diffusion would be faster. This is contrary to the results that I have gotten. When I compare to other groups, the results are also about the same. I think that this might be attributed to random error during the experiment.

Lastly, test tube E contains chopped beetroot discs submerged in 4ml of water. Its I/O-1 is 80.3%, and it is observed as having a pale red colour, which is redder than A and D but lighter than B. This might be because the chopped beetroot discs have a larger exposed surface area to volume ratio, and hence the pigments from the chopped beetroot can travel out of the cells into the water more rapidly through osmosis. Hence, its I/O-1 would be relatively low as compared to A and D, but higher than B and C because the external solution is not hypertonic to the beetroot cells. From the above data analysis, I generalize that the rate of the leaking of pigment out of the beetroot cells is determined by two factors – the external environment in which they are submerged in, as well as the surface area of the beetroot discs. As the external environment of the set-up is more hypertonic, the rate of diffusion would occur faster. As the surface area to volume ratios of the beetroot discs are larger, the rate of diffusion would occur faster as well.

In order to make sure that the natural variation of living things is minimized, I can repeat the experiment a few more times to ensure accuracy.

Conclusion In conclusion, the data collected has supported my hypothesis, that the 4ml of 50% alcohol in which the beetroot cells are submerged in would contain the most amount of pigments diffused from the beetroot cells.