How does water get to leaves at the top of trees? Or… Suck It Up!
Introductory YouTube: https://www.youtube.com/watch?v=VbQk8p3qgo8 (or just read this)
STOP AND THINK
If trees get water from their roots, then how does the water get to the leaves, including those at the top of the tree? (What do you predict? Record in your science journal.)
ACTIVITY PLAN
Experiment using one of three models of how trees might send water upwards (A.B.C below). Choose based on what is available to you and do all the experiments if the materials are all available.
A) Put plants such as celery, green onion, an iris (leaf and flower) or a big, flat leaf off of a house plant in water with red or blue food coloring for a day and then observe what has happened. OR – if you do not have celery, green onions, big flat leaves – but you do have food coloring, try “B”..
B) Put colored water in the end and middle cups of 5 clear plastic cups, leaving the cups on either side of the middle cup empty of water. Put folded paper towels between each cup, making sure that the paper towel extends into the water. Observe what changes occur over a day. OR – if you do not have food coloring or celery, green onion, etc., but do have an extra paper towel and two cups or glasses, try “C”….
C) Put one cup of water in a clear glass. Tightly fold up a paper towel lengthwise (so it is long but narrow)
WHAT YOU DO
1) Chose which experiment or experiments that you are going to do.
2) Get out your science notebook.
3) Set up the experiment you are going to do by looking at the pictures of Experiments A, B, and C below.
4) Make a drawing in your notebook of the set up of the experiment.
5) Predict what will happen in one day in each experiment you do. Record in your science notebook.
6) Observe what happens during the next 24 hours (approximately) and write down observations.
WHAT HAPPENED?
Look at the pictures below! Or see summary YouTube at:
https://www.youtube.com/watch?v=9VNBOy0r7O8
Experiment A:
Where did the colored water go? How can you tell where the colored water went?
**Hint: Be sure to slice the celery and/or plant leaves across the stem or leaf (not up or down). Is the colored water spread out evenly? Make a drawing in your notebook of where the colored water is concentrated. In the celery you can pull out the colored “tubes”. How did the water move up?
Explanation: It moved up in thin tubes that run up through the plant. You can pull out each tube in the celery and see that it is filled with red water.
Experiment B:
At the start, there were two empty glasses. How many empty glasses are there now? How did water get from one glass to another?
How can you tell that the water moved up through the paper towel and down into the empty glass?
Where did the green water come from? (THINK: what colors of paint mixed make green?)
Where did the orange water come from? (THINK: what colors of paint mixed make orange?) How did the water move up and down?
Explanation: It moved through small spaces in the paper towels.
Experiment C:
What happened to the empty glass?
Where did the water come from?
Compare the amount of water in the 2 cups. Which has more, which less or are they about
the same?
How did the water move up and down?
Explanation: It moved through small spaces in the paper towels.
HOW CAN THE WATER MOVE UP (AND DOWN)?
The water molecules tend to stick together. But they tend to stick even more to other material, such as the side of a tube in a plant, or to the sides of small spaces in paper towels. The force sticking the water to the side of the tube is greater than the force of gravity pulling it down. The attraction for the side of the tube or the sides of the spaces in the paper towel is strong enough that the water keeps moving upward through the tube.
The water will only move up if the tube is narrow so a lot of the water can touch the side of the tube.
EXTEND: TRY THIS!
Cut a straw and the cardboard tube from a roll of paper towels or a roll of toilet paper to the same length.
Try sucking up water through the cardboard tube and through the straw.
Which is easier to suck up water through – the cardboard roll or the straw?
Why? (One reason is that you have to suck up more water in the big tube. Another reason?) Write your thoughts in your journal.
CONCLUDE
Explain what these experiments show about how water gets from the ground to the top of trees.
Write the explanation in your science journal.
ADDITIOAL RESOURCES AND EXPLANATION
https://www.usgs.gov/special-topic/water-science-school/science/surface-tension-and-water?qt-science_center_objects=0#qt-science_center_objects
https://www.usgs.gov/special-topic/water-science-school/science/surface-tension-and-water?qt-science_center_objects=0#qt-science_center_objects
https://www.usgs.gov/special-topic/water-science-school/science/adhesion-and-cohesion-water?qt-science_center_objects=0#qt-science_center_objects
Experiments
https://www.youtube.com/watch?v=w_tc8tlEoBs
Water is actually transferred from one glass to another.
https://www.youtube.com/watch?v=y-h_qGhgtno
Time lapse movie of withering plant coming to life with water – a MUST SEE!
https://www.youtube.com/watch?v=KIug9Foou3s
An explanation of water movement in celery.
AND THERE IS MORE TO IT
If you thought that this process (capillary action) could not by itself transport water to the tops of trees, you are so right. Leaves have openings called “stomata” through which water is released through transpiration. Water transpired by trees produces the haze of the “Smoky” Mountains. Water released into the atmosphere by the leaves lowers the water pressure at the site of the leaves. Water lower in the system is under higher pressure and moves upward to remove the difference in pressure. This important process works in conjunction with the capillary action investigated here. What do you think the Water Cycle has to do with all of this?