Science you can see: plants and plant products

Plants grow all around us – in the garden, in fields, in tropical forests, in the desert, in water and even inside in pots.

They can be very big, like Redwood (Sequoia) trees, which are a thousand years old and 15 storeys tall, or they can be very tiny, like individual duckweed (algae) cells, which you can hardly see. New varieties of plants can be produced by breeding experiments or more recently, by genetic engineering.

Plants all need light, water, air and food to grow.

Plants are essential for life on our planet. They take up carbon dioxide in the air that they use to grow, and produce oxygen, which animals need to breathe. They provide shelter for animals - birds live in nests in trees, insects make their homes in plants, and forest animals ranging from monkeys to mice need plant cover to survive from all types of weather, and to safely hide from predators.

Plants provide people with products to help us live comfortably - wood for houses, cotton for clothes, wood fuel for fires to keep warm and to cook, paper to write on comes from trees, and of course, all sorts of healthy foods, our fruit and vegetables, wheat and corn for cereals, rice and nuts, and drinks like soy milk, wine, tea and coffee.

Also, plants can be processed to extract medicines and colourful dyes. Tea trees, and eucalyptus (gum trees), lavender, peppermint, and sandalwood are used in perfumes and ointments. Most Indigenous people have a host of natural remedies based on plant extracts for treating cuts, burns, allergies and sore muscles. Chinese medicine relies heavily on herbs and medicinal plants.

Plants are also beautiful to see and can have lovely perfumes.

Experiments with plants

Making food dyes

Many of our processed foods are coloured with food dyes, some of which come from plants. We can ‘extract’ colours from many plants by just grinding up some plant with water.

Try this with some grated carrot.

• Put it on a white saucer or white dish with a spoonful of water. 
• Using a wooden chopstick or an icy pole stick, stir and crush the bits of carrot for a few minutes.
• You will see the orange (carotene/Vitamin A) dye dissolve in the water. 
• Soak up this orange water with a cotton bud or a cotton wool ball to see the orange tinge. 
• You have actually ‘dyed’ the cotton with the plant extract.

For other colours try grating and extracting green zucchini skin, red and green capsicum, dry currants (gives nice purple colour!), frozen blackberries, raspberries or even some parsley.

Colours in flower petals

The availability of flowers will depend on the time of the year. Traditionally spring is the best time for flowers but some varieties are available at other times. Irises, geraniums and roses seem to bloom for extended periods, whereas daffodils, jonquils and camellias signal the end of winter.

With a similar water extraction method, try to extract some of the variety of colours from flower petals. Look around your garden. Purple iris petals are some of the best, but try pink geraniums, red rose petals, yellow gerberas, orange lilies. These pretty colours can also be used to dye your cotton buds and the cotton balls.

Chemicals from tree bark

Take a little bit of bark from a wattle tree or a gum tree, maybe an iron bark tree or a stringy bark, and crush this up in water like you did with the grated carrot. The dark tan colour will soon appear in the water.

Australian Aborigines have used tree bark extracts for centuries to treat aches and pains and as an antiseptic for cuts. Wattle bark was first exported from Australia nearly 200 years ago, to be used in the tanning industry in the UK. The tanning process preserves animal hides by mixing hides with the bark chemicals (tannins) to stop the leather proteins from rotting.

Colour chromatography of plants

In 1906 Michael Tswett, a Russian scientist invented the term ’chromatography’ (Greek words ’chroma’ meaning colour, and ‘grapho’ meaning write/draw) to describe the process he discovered for separating out the coloured pigments from plants.

He was interested in purifying chlorophyll, the green pigment in plants from the other yellow and red pigments. He did this experiment by putting a crushed up sample of a plant on top of a glass tube filled with mineral sand (calcium carbonate), and washing it through with a liquid such as ether or alcohol. As the sample washed through, individual bands of colour separated.

Chromatography has now developed into a billion dollar industry for separating and purifying mixtures of chemicals using sophisticated technologies. Thus gas chromatography and high pressure liquid chromatography are used in medical, industrial and environmental applications.

Chromatography experiments

We can do some interesting chromatography experiments using simple household equipment and fresh plant material or frozen berries.

Paper coffee filters (brown will do) provide suitable paper and just water (or diluted vinegar) can be used as the solvent (rather than toxic ethers, acetones or alcohols). Although this system will not separate pigments like Tswett’s petroleum ether mixture, you will get some effects. The colours in the flower petals of red cyclamen, purple pansies or purple petunias can provide some fun, or frozen blackberries or blackcurrants.

Cut the coffee filters into rectangular strips about 2 cm wide and as long as possible (at least 10 cm depending on the size of filters you have bought at the supermarket). Try not to touch the paper too much as you will leave grease from your hands on it. Also keep the paper very dry before the experiments.

Experiments with plant samples (difficult)

• For a flower petal, place the petal about 1-2 centimetre from one end of the paper strip, and using the edge of a coin press a line of petal colour very carefully onto the paper. Go over the line a few times with a different part of the petal until you have ‘loaded’ the paper with a fair amount of coloured pigment.

• Then using a plate with a little shallow puddle of a few drops of water on it, carefully dip the very edge of the paper strip near the pigment line in the water. Don’t allow the pigment sample to touch the water, and just let the water slowly soak up the paper strip. It might take a couple of minutes.
• You will see a streak of water-soluble colour move up with the leading edge of the water ‘front’. When the water has soaked up to your fingers, take the paper away from the water and put it on a clean dry plate to dry. Each type of flower petal will show a different and characteristic pattern of pigment separation. Your ‘chromatogram’ should show some separation of the red and blue pigments, which make up the red/purple colours.
• The blackberries and raspberries can be just ‘spotted’ 1cm from the bottom of strips of filter paper in a similar way, and blue and red dyes may separate out.
• Different colour patterns can be distinguished with this plant chromatography using vinegar diluted to half strength in place of water.

Chromatography experiments with coloured marker pens (easier)

It is much easier to get some stunning separation of colours doing chromatography using coloured marker pens containing ‘water based’ dyes. (Don’t try water fast/permanent/waterproof/permanent pens, as the dyes won’t separate using water). The cheaper the pack of pens the better!

• Make a spot of colour with a pen, about 1.5 cm from the bottom of the strip of coffee filter paper. 
• Let it dry for a minute, and then carefully put the edge of the paper near the spot in some drops of water on a plate. 
• Remember: Don’t dip the spot into the water directly. Allow the water to run up the paper strip.
• Spots from brown pens will split into blue, red and green patches, black pens will give several colours as well. 
• Purple and some dark blue pens also separate into a mixture of colours in about one minute of careful chromatography. Good luck with this!

Patterns with coloured markers on tissue paper (easiest)

Take a white paper facial tissue and place it flat on a white plate. Make a small circle of dots (about 1 cm in diameter) with a marker pen (black, brown and purple are best.) Then carefully drip water (about five drops) into the centre of the circle you have drawn. Watch the coloured dyes from the markers separate out as the water circle spreads. Try mixtures of coloured dots in the centre of the tissue paper.

This can also be done on single layers of the coffee filters to yield beautiful patterns.

Further Resources:

New medicines from plants:  http://www.environment.gov.au/biodiversity/publications/articles/drugs.html

Chemical education journal – Plants, chromatography and other separations http://chem.sci.utsunomiya-u.ac.jp/v7n2/livneh/livneh.html#Anchor365710

Important note: All activities are designed to be performed under the supervision of a responsible adult, who is aware of any conditions that might preclude the safe participation of the child with regard to allergies to food, or other household or environmental agents.

Article written by Kathy Andrewartha (B. App. Sci., M.Sc., B.A., Grad Dip. Info. Sci.). Kathy studied Biochemistry at Swinburne and La Trobe Universities and has worked on research topics involving both plants and animals. She enjoys teaching science at all levels. She particularly likes presenting science to young children, and is passionate about stimulating active learning and analytical thinking about scientific topics.