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Description

How does water travel through a plant?
In this experiment, we will use coloured water to see how water travels up a plant’s stem.

Resources

You can use:
A white carnation, or
A pale celery stalk with leaves attached
Celery often shows the coloured tubes in the stem very clearly.

You will need
1 white carnation or celery stalk
1 clear plastic cup
Water
Food colouring
A teaspoon or stirring stick
Adult scissors or secateurs
A label or sticky note
A pencil
Paper for recording your observations

Instructions

Science and safety rules
Do not drink the coloured water.
Do not put the flower, celery or food colouring in your mouth.
Food colouring can stain hands, clothes and tables.
Keep the cup standing upright.
Tell a leader immediately if anything spills.
An adult must cut the flower or celery stem.
Wash your hands when you have finished.
Before you begin

Look carefully at your carnation or celery.

Think about:

What colour is it now?
Where do you think the colour will appear?
How long do you think the change will take?

Write or draw your prediction.

I predict the coloured water will…

Instructions
1. Prepare your cup
Write your name or group name on a label.
Stick the label to the cup.

2. Add the water
Half-fill the cup with water.
Do not fill it to the top because the water could spill when you add the plant.

3. Add the food colouring
Add approximately 10–15 drops of food colouring to the water.
Dark colours such as blue, red, green or purple are usually easiest to see.

4. Mix the coloured water
Use a teaspoon or stirring stick to mix the water gently.
The colour should be strong and easy to see.

5. Prepare the carnation or celery
Ask an adult to cut approximately 2–3 cm from the bottom of the stem.
The adult should make the cut at an angle. This gives the stem a larger surface through which it can take in water.
If you are using celery, keep some leaves attached to the top.

6. Put the plant in the water
Place the cut end of the carnation or celery into the coloured water.
Make sure the bottom of the stem is under the water.

7. Make your first observation
Look closely at the plant.
Record what it looks like at the beginning of the experiment.

You can:
Draw a picture
Write a short description
Record the time
Take a photograph

8. Leave the experiment somewhere safe
Place the cup somewhere it will not be knocked over.
Leave the plant in the coloured water.
Try not to move it while the experiment is working.

9. Check for changes
Check the plant after:

30 minutes
1–2 hours
At the end of the meeting
The following day

The change may be small at first. Look very closely at the edges and veins of the petals or leaves.

10. Record your results
Draw or write down what has changed.
If you are using a carnation, look for colour:
Along the edges of the petals
In the veins of the petals
In small lines running through the flower

If you are using celery, look for colour:

In the leaves
In the veins of the leaves
In small dots or tubes inside the stalk
What is happening?

Plants need water to survive. Normally, a plant’s roots absorb water from the soil.
The water travels upwards through tiny tubes inside the stem. These tubes are called xylem.
The coloured water moves up the xylem to the leaves or flower. As the water reaches the top, the food colouring makes the route easier for us to see.
Water is pulled upwards partly because water evaporates from the leaves and petals. This process is called transpiration.
It is a little like drinking through a straw, although the plant does not have a mouth or actively suck up the water.

What should you see?
If you use a white carnation

The edges or veins of the white petals should gradually change colour. You may see a small change after a few hours, but the result will usually be clearer the following day.

If you use celery
Coloured lines may appear in the leaves and stalk. If an adult cuts across the celery after the experiment, you may see coloured dots inside the stem. These dots are the bundles containing the xylem tubes.

Extra experiments

You could also investigate:
Does warm or cold water travel through the plant more quickly?
Which food-colouring colour is easiest to see?
Does celery change faster than a carnation?
What happens if you leave one plant in plain water?
What happens if an adult carefully splits a carnation stem and puts each half into a different colour?
Remember

Predict → Prepare → Observe → Record → Explain

Tags

• colour change
• experiment badge
• Let it grow
• science

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