Particularly striking and important colours are reds and yellows. They are found hidden all over the world: in tulips, eggs, fish... They all have something in common. In this experiment, you can take a look at nature's tricks and discover the secret of her colours.
Let's go - have fun!
Why do crabs change colour? Where does the colour yellow come from exactly? What is colour actually made of? And what does lipophilic or lipophobic mean? Below you will find additional information on where the colours of animals and plants actually come from. You will also find links to information material that we have found online on the topic!
Suitable for age group: 10-14 years
Especially interesting for: Hobby botanists, plant experts and future researchers
Preparation time: ca. 40 min + a bit of a wait
For the experimental setup:
Mortar with pestle
Test tube (e.g. an empty vanilla bean tube)
Test tube holder (alternatively a narrow, stable glass)
Teaspoon (easier with a pipette or an empty eye dropper)
Needed for the experiment:
A bouquet of red and yellow tulips
Filter paper (e.g. white coffee filter paper)
Highly pure quartz sand (e.g. fine quartz sand for the aquarium)
Methylated spirit (without acetone and HCl)
Colourless baby oil
Step 1: Harvesting the Petals
First you need to pluck the petals from three tulip flowers (that's about 18 petals) and cut them up as finely as possible with the scissors.
Step 2: Make a paste of the blossoms
Next, place the petals in the mortar with a teaspoon full of quartz sand and a little (2 - 3 teaspoons) of methylated spirit and grind them vigorously.
As soon as the mixture starts to become doughy, continue to grind patiently for a few minutes and gradually add as much methylated spirit as necessary until a pourable, deep red colour solution is formed.
The longer the flowers are ground, the more dye is dissolved and the more beautiful the reaction becomes.
Step 3: Prepare the funnel and pour off the paste
Place the funnel in the test tube and line it with filter paper folded several times in the middle. For this purpose, cut the filter paper into a circle.
Then pour the contents of the mortar into the funnel and wait until the solution has run through the filter paper into the test tube.
Unfortunately, this cannot be said exactly, because each of you will get a different amount of filtrate. The filtrate is what remains after filtering. But with the sketch on the left you can estimate approximately how much oil and water you need to add.
Step 5: Wait and observe
Now you can sit back and relax and watch your glass.
Gradually you can observe a so-called phase separation. This means nothing other than that the oil and the water separate again. You may have observed this phenomenon before when making salad dressing.
In your experiment, the oil has taken on a yellow colour and is the upper phase in your test tube. Meanwhile, the water is red. This phase is in the lower part.
The longer the test tube is left to stand, the more yellow the upper oil phase becomes.
For our experiment, the plastids in the cytoplasm and the vacuole are the most interesting. Plastids are small cell organs which include chloroplasts, chromoplasts and leucoplasts. Chloroplasts mainly carry the pigment chlorophyll (green) and chromoplasts mainly carotenoids (yellow). Under certain conditions, a pigment can also accumulate in the vacuole, namely anthocyanins (red).
In the upper oil phase, the fat-soluble (lipophilic) flower pigments which are contained in the chromoplasts of the cells of the tulip flower accumulate. In the lower water phase, the water-soluble (lipophobic) flower pigments are concentrated, which are contained in the vacuoles of the cells of the tulip flower. The more patiently we ground the petals with the sand in the mortar, the more cells, vacuoles and chromoplasts have been broken apart and the more pigments have been dissolved in alcohol (ethanol). In contrast to water and oil, lipophilic and lipophobic substances dissolve equally in ethanol.
The red, water-soluble flower pigments of the tulip are anthocyanins.
The yellow flower pigments of the tulip dissolved in the oil are carotenoids.
Most carotenoids are fat-soluble pigments (dyes). Although they do not all have the same colour, they are grouped together based on their chemical structure (tetraterpenes, from eight isoprene units). They can normally only be newly synthesised (produced) by microorganisms, fungi and plants. Humans and animals, on the other hand, for which carotenoids are also essential for survival, cannot produce them themselves and must ingest them with their food. The only exception is aphids, in which several species have acquired the gene for carotenoid production from fungi. This works thanks to so-called horizontal gene transfer.
Carotenoids criss-cross the food chains. They are responsible for the "yellow in the egg", the redness of koi, goldfish and salmon meat. They are responsible for blue crabs (lobster, shrimp,...) turning red in hot water. They are the reason for the yellow beak of the mallard drakes, which vie for the favour of the ducks (the more yellow the beak, the better the drake looks to the ducks) and many more.
For us humans, beta-carotene is the precursor to provitamin A and is important for our immune system and the visual process, among other things. That's why they say you should always eat your carrots so that you can see better.
Crack an organic egg and a conventional egg into a transparent glass and compare the colour of the yolk. Most conventional laying hens are fed so much carotenoid-enriched feed that the yolk appears almost reddish-orange. Organic farms also add carotenoids but rarely to the same extent. If you break open organic eggs from different sources, you will find the most varied shades of yellow.
When you have seafood for dinner again, throw a blue shrimp into a transparent glass of hot water. During boiling, you can see that the initially blue animal gradually turns red. The protein component of the blue protein-carotenoid complex denatures (breaks down) and the red carotenoid with the illustrious name astaxanthin becomes visible.
Created by Dr. Simone Gaab, Dr. Thassilo Franke, Sandra Kollmansperger
Menzinger Str. 67
80638 München, Germany
Phone: +49 (0)89 178 61-411
Phone: +49 (0)89 178 61-422
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