Use a celery stalk to explore the movement of water in plants.
Developing SkillsPredicting, Observing
What you need
- Celery Stalk
- Clear cup
- Food Colouring (Blue, red and purple work well)
Safety First! Cut the celery for younger children. Use caution with sharp knives.
What to do
- Cut a long stalk off of a head of celery.
- Fill a clear cup 3/4 full of water.
- Add 10 drops of food colouring to the water.
- Place the celery stalk in the cup. What do you think the celery will look like tomorrow? What about the water in the cup?
- Put the cup in a safe place overnight and observe the following day. Does the celery look the same or different? Describe what you see. Explain what you think has happened.
Just like animals and humans, plants need water to survive. Plants get the water they need from their roots. Root systems are designed to go deep into the soil and absorb water and nutrients. Roots bring water into the plant and xylem (tiny tubes) carries the water to the rest of the plant. Xylem is a system of hollow tubes that act like straws in a plant. It allows the plant to draw water up its stalk or stem. Sometimes celery has "strings," which are several xylem tubes grouped together. Did you know that a celery stalk is not a stem? It is actually the part of the leaf called the leaf stalk. This is why we call the part of the celery that we eat the stalk.
When water gets to the leaves at the top of the plant, it evaporates through tiny holes in the leaves in a process known as transpiration. Transpiration results in evaporation of the water at the top of the xylem. More water is then pulled from the roots to keep the xylem full.
Why does it matter?
Xylem not only helps plants by providing them with the water they need, xylem also helps to provide structural support for the plant. The rings you can see in a cross-section of a tree's trunk are actually old xylem. They make wood hard enough to be used as a building material.
- Observe the progress of the water in the celery stalk. Check it by peeling away part of the stalk after 1 hour, 2 hours, 4 hours, etc. What is the depth of colour at different times? Does the water move faster or slower than you expected?
- Try this experiment again. This time, put one celery stalk (in water and food colouring) in a well-lit place and another celery stalk (in water and food colouring) in a dark place. Is there any difference to what happens to the colouring? What could explain this?
- Try this experiment again. This time, put one celery stalk in a cup with water and food colouring and another celery stalk in cup with water and food colouring that you have added one spoonful of sugar to. Is there any difference to what happens to the colouring? What do you think is going on?
- Try the experiment with other types of plants. White flowers with long stems such as daisies and carnations work well. Do flowers change colour as the celery leaves did? What do you think is going on?
- Try other colours of food colouring. Which colours can you see the most clearly in the celery stalk?