Practical 2 – Effect of Environmental Conditions on Beetroot

Aim: To investigate the factors affecting the cellular homeostasis of Beetroot cells

Materials:

  • Razor blade
  • Ruler
  • 5 test tubes and rack
  • Forceps
  • Distilled water
  • 25% and 50% alcohol solution
  • Beetroot (Beta vulgaris)
  • White tile (for cutting)
  • 3 droppers (water, 25%, 50% alcohol)
  • Thermometer
  • Stopwatch
  • 2 beakers
  • Tripod stand and wire gauze (for water bath)
  • Colorimeter

Procedure:

1. Set up a boiling water bath with the bigger beaker. When the water starts to boil, turn off the Bunsen burner.
2. Use a ruler and scalpel to cut the cylinder of beetroot into 25 discs of 2mm each.
3. Take 5 discs of beetroot and cut them further into smaller pieces.
4. Rinse the beetroot discs and pieces until the water is colourless.
5. Label and prepare 5 test tubes as follows:

Tube Content
A 4 ml of water
B 4 ml of 25% alcohol
C 4 ml of 50% alcohol
D 4 ml of hot water (900C – 1000C), in water bath
E 4 ml of water with chopped beetroot

6. Place 5 discs of beetroot in tube A – D and all the chopped beetroot in tube E using the forceps.
7. Leave the tubes to stand in your test tube rack for 15 minutes.
8. Shake the tubes gently after 15 minutes and hold it against the white tile to note the colour. Record your observations in a table. (You should be constructing a table during the wait time)
9. Use the colorimeter to record the percentage of transmission of light.
10. Decant a small amount of the liquid from each tube into a cuvette to measure the percentage of transmission. Hold the cuvette only at the ROUGH sides. Turn the cuvette so that the arrow is facing you when you insert it in to the colorimeter.
11. Dispose of the content of the tubes after the experiment. Please do NOT throw the beetroot into the sink.
Results
Before

Tubes A, B, C and E (from right to left)

2014-01-21 12.38.35

Tube D

2014-01-21 12.38.43

After

Tubes A, B, C and E (from right to left)
2014-01-21 12.48.12

Tube D
2014-01-21 12.48.16

Colour observations

Tube A
Very pale red

2014-01-21 12.48.48

Tube B

Pale red

2014-01-21 12.49.14
Tube C

Very red
2014-01-21 12.49.40

Tube D

Extremely deep red
2014-01-21 12.50.01

Tube E

Red
2014-01-21 12.50.20

Colorimeter readings (results taken are 1-5)

2014-01-21 12.55.07

Discussion questions
Background knowledge
Beetroot contains a red betalain pigment in the vacuole.
1.    Why was it necessary to wash the beetroot slices thoroughly before using them in this exploration?

The beetroot cells contain a red pigment within the vacuole. After the beetroot slices have been cut, their vacuoles may have been damaged, causing the pigment to leak out. Therefore the leaked pigments have to be washed off so as to not contaminate the solution before the start of the experiment.

2.    Identify the independent and dependent variables in this experiment. Which was the control set-up for this experiment?

Independent variables: temperature of water, concentration of alcohol solution and exposed surface area of beetroot slices

Dependent variable: percentage of transmission of light of the colour of liquid in the test tubes

Control set-up: Tube A

3.    Construct a suitable table, with appropriate headings and units, to tabulate your data.
4.    Explain, with reference to the tabulated data, the effect of different solutions in tubes A-C on the readings obtained in the experiment.  You should make reference to the knowledge you acquired from the lessons on cell structure and cell membrane.

(The alcohol solution dissolves lipids in the cell membrane, thus making it more porous and allowing the red pigments in the vacuole to leak out of the cell and into the solution. Therefore, Tube B containing 25% alcohol allows only 84.57% of light to pass through the liquid compared to the control set-up Tube A containing only water, which allows 87.1% of light to pass through. With a greater concentration of alcohol in the solution, the cell membranes become even more porous. Thus Tube C containing 50% alcohol allows even less light, at 52.59%, to pass through.)
5.    Suggest an explanation for the observations of tube D & E.

(Only 26.83% of light could pass through the solution in Tube D, due to the high water temperature which denatured the proteins in the beetroot’s cell membranes, making it porous and allowing the red pigment to leak out and block light in the solution. In Tube E, only 38.17% of light could pass through as compared to Tube A with 87.1% of light passing through. This is because the greater surface area to volume ratio of the beetroot pieces greatly increased the rate of diffusion of the red pigments out of the cell.)

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s