Biology Beetroot Coursework

 

                                            Figure 1 http://www.infoplease.com/images/cig/biology/02fig01.png

Beetroots contain a red pigment called betalain which is found in the vacuole of the cell. When the beetroot is heated the cell membrane becomes disrupted as an increase in temperature provides an increase in kinetic energy making the phospholipid bilayer (in cell membrane) vibrate more energetically until the hydrogen bonds holding the 3D structure of the proteins together breaks therefore denaturing the selectively permeable cell membrane. This allows red pigment to leak from the vacuole and out of the cell by diffusion as an increase in temperature also increases the rate of diffusion. Diffusion is the net movement of molecules or ions from a region of their higher concentration to a region of their lower concentration using their own kinetic energy. An increase in temperature also increases fluidity of the membrane as the proteins vibrate with more kinetic energy to a greater amount creating gaps in the plasma membrane allowing pigment to diffuse out.

Prediction:

I predict that as the temperature increases, the beetroot will become more permeable and will release a higher concentration of red pigment called betalain. This permeability will be detected due to a colour change from light to dark purple.

Justification of Prediction

Justification of Method

I conducted an experiment to test out the hypothesis and to prove the prediction to be true or false by using one specific process. There are many ways I could have used to do this but I had chosen not to.

All living organisms are surrounded by membranes, so I had a wide choice of sources to choose from. I had access to beetroot, potato, carrot and liver. I decided not to use potato because, although it is cheap and readily available, it tends to break down very quickly, and this is shown in the dark colour it changes into. This means that the potato cells will have begun to deteriorate and would not give me very accurate results. I decided not to use liver as the source because it loses mass very rapidle.

Apparatus needed:

• Water tank
• 6 Test Tubes
• A Test Tube Rack
• 1 Whole Beetroot
• Sharp Knife
• Ruler
• Scalpel
• Forceps
• Tile
• Spatula
• Calorimeter
• Cork Borer (Size 5mm diameter)
• Stop Clock
• Thermometer
• 16 Cuvettes
• 10cm3 pipette

Method

1. Use a cork borer to cut out a cylinder from a beetroot.
2. Using a ruler and scalpel, cut the cylinder into a series of discs with the same size and thickness, approximately 5mm on the tile. There will need to be at least 24 discs ready. This size ensures a large surface area for the heat to act on the beetroot.
3. Place water in a Petri dish and rinse the beetroot discs carefully. This will remove any of the pigment that has spilled out of the cells when they were cut.
4. Place a fixed volume of about 10cm3 into each of the six test tubes using the 10cm3 pipette.
5. Place 2 beetroot discs into each of the test tubes.
6. Leave one test tube at room temperature, making sure that a thermometer has clarified the room temperature to about 20°C - 25°C.
7. Place the remaining test tubes in water baths of different temperatures such as 45°C, 55°C, 65°C, 75°C and 85°C. Make sure that the thermometer has clarified the temperatures to be exact as this will ensure accuracy. This ensures a good range and will make sure that a distinct difference is recognised.
8. The test tubes should be left in the water baths for approximately 40 minutes, making sure that the time is the same for each test tube. This time makes sure that the contents of the test tube have reached the temperature of the water bath and had long enough to affect the cell membranes and to detect a difference.
9. All of the test tubes should now be removed from their water baths and placed onto the test tube rack as swiftly as possible, to ensure accurate readings.
10. Gently mix each of the test tubes for a few seconds (making sure that each tube is mixed for the same amount of time to ensure accuracy of results) so that the contents of the liquid are evenly distributed.
11. Now the liquid can be separated from the beetroot disc. This can be done by using a syringe and placing the liquid into a cuvette, making sure that all the tubes are the same size.
12. Use a calorimeter to measure the absorbance of each cuvette compared to the absorbance of just plain distilled water and this will give a distinct comparison to show different absorbencies using different temperatures. The calorimeter will ensure that precise, numerical readings are taken.
13. Repeat the experiment 3 times for each of the different temperatures to ensure that the results are reliable if the results are similar.

Variables