Beetroot

1

Beetroot pigmentsA recipe for cooked beetroot usually

recommends that yo udon’t cut the stalk or remove the skin. If you ignore these warnings you are likely to end up red handed. Beetroot contains red pigments called betalains, located within the cell vacuole. Normally the pigments can’t pass through cell membranes but they leak out when the beetroot is cooked. You’re going to figure out what changes.

The aim of this practical is to use beetroot to examine the effect of temperature on cell membranes and relate the effects observed to membrane structure.

Planning What do you think will happen? and what

biological knowledge are you basing this on? Use this to write a testable hypothesis.

Have a look at this procedure, are you going to get enough measurable information to validly test your hypothesis?

Is the apparatus suitable? are you aware of the variables involved? Can you control them? Can you measure effectively?

Can you think of any alternatives if you need to change anything?

What risks are involved to you and others? How can you prepare for them? What safety precautions are needed?

You need Raw beetroot

Size 4 cork borer

White tile

Knife

Ruler

Water baths at different temperatures

Plastic beaker, about 250 cm3

2 boiling tube racks

Crushed ice

8 boiling tubes

Thermometer (one per water bath)

Colorimeter

Cuvettes

Stopclock

Distilled water

Pipette for measuring 2 cm3

Small measuring cylinders

Why does the colour leak out of cooked beetroot?

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BIO

LOG

Y C

OR

E PR

AC

TIC

AL 2

4 S

epte

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er

When you cook with beetroot you always end up red handedbut why does this happen? What changes occur between raw and cooked beetroot?

2

AS

BIO

LOG

YC

OR

E PR

AC

TIC

AL 2

4 S

epte

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008

Procedure

Cut sections from a single beetroot using a size 4 cork borer. Cut eight, 1 cm length slices from these sections. Be careful not to spill beetroot juice on your skin or clothing as it will stain very badly.

Place eight labelled boiling tubes each containing 5 cm3 distilled water into water baths at 0 °C, 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, 60 °C and 70 °C. Leave for 5 minutes until the water reaches the required temperature. Place one of the beetroot sections into each of the boiling tubes. Leave for 30 minutes in the water baths.

Remove beetroot sections; shake the water/solution to disperse the dye.

Switch on the colorimeter and set it to read % absorbance.

Set the filter dial to the blue/green filter.

Using a pipette accurately, measure 2 cm3 distilled water into a cuvette. Place the cuvette into the colorimeter, making sure that

the light is shining through the smooth sides.

Adjust the colorimeter to read 0 absorbance for clear water. Do not alter the setting again during the experiment.

Place 2 cm3 of the dye solution into a colorimeter cuvette and take a reading for absorbency. Repeat the readings for all the temperatures.

Present your results in an appropriate way.

Identify any trends or patterns in your results.

Explain any trends or patterns, supporting your statements with evidence from your data and using biological knowledge. You can find out more about the biochemistry of the main components of the cell membrane in the textbook and in the interactive tutorials on lipids and protein structure.

Describe how you could have improved this experiment to give more reliable results.

Which temperatures are showing the most release of colour and which the least?

What colours? The colorimeter will tell you how much of the beetroots ‘red’ has been leaked out.

Plan an investigation to investigate why handling raw red cabbage does not make fingers very red but handling pickled cabbage does.