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Nature’s colours

By Chenxin Tu, 27 January 2023

Plants are packed with colourful chemicals that we call pigments

Have you ever sat in a garden or park and noticed all the different colours in plants? In this activity, you can dig deeper into nature’s colours and find out the variety of pigments that give each plant their unique colours.

Safety: This activity involves collecting and handling leaves, and also hot water. Ask an adult to help.

You will need

• Leaves or petals from your garden
• Small cups
• Bigger trays or containers to put the cups into
• Small jug
• Scissors
• Paper
• Rubbing alcohol

What to do

1. Collect a few different types of leaves from your garden. Don’t pick spikey or tough leaves – you need to cut them up in the next step. If you want, you can also use flower petals.
2. Cut up each type of leaf into small pieces and then put each type of leaf into its own cup. If a leaf is hard to cut up, try a different type of leaf instead – you don’t want to accidentally hurt yourself!
3. Pour some rubbing alcohol into the cups, using just enough to cover the leaves.
4. Place the cups onto trays.
5. Use a small jug to pour hot (not boiling) water into the trays to warm the cups up.
6. Cut up strips of paper about 2cm wide and long enough to reach the bottom of your cups, and place one strip of paper into each cup.
7. When everything is set up, wash your hands and then leave the cups and paper strips overnight.
8. Take out the paper strips and lay them out on a clean surface. What do you see?

What’s happening?

Plants come in all kinds of colours. From flowers to fruit, there are heaps of colourful plant parts to look at. Added to this, plants use their green leaves to turn sunlight into energy. It shouldn’t come as a surprise that plants are packed with colourful chemicals that we call pigments.

By cutting the plant leaves and soaking them in rubbing alcohol, we can pull these pigments out of leaves. Adding hot water around the mixture speeds up the process. When we put paper into this leafy liquid, it gets sucked up. Colourful pigments get pulled along for the ride, but they stop at different spots. The most easily dissolved chemicals make it further up than the less dissolvable ones.

What chemical is that?

So what chemicals can you spot in your strips? Here are a few you might know about.

All plants use chlorophyll to turn sunlight into food. There are two main types of chlorophyll that can be found in green leaves. Chlorophyll a is a dark green colour, while Chlorophyll b is yellowish green. Chlorophylls are hard to dissolve and will not travel far up the paper.

Carotenoids make plants look red, orange, or yellow to us. For example, beta-carotene (a type of carotenoid) gives carrots and sweet potatoes their orange looks!

Flavonoids are the plant pigments that make red, blue, yellow, and purple. The most common flavonoid is anthocyanin, which makes up the red that we see in many roses, apples, and autumn leaves. Another group of pigments called the betalains also give some plants red and yellow colours.

Carotenoids, flavonoids and betalains are easier to dissolve than chlorophylls and will travel further on the paper strip.