Leaf Suction Investigated

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Leaf Suction Investigated

On of the major unanswered questions regarding plants is how water moves from the ground and up into the leaves - especially the leaves at the top of a 350 foot tall tree. You may read more about this problem and about how to investigate various other aspect if you click this button: . You may also want to look at another of the newspaper's weekly inserts by clicking this second button: .
We are going to do what scientists like to do: look at just one aspect of the overall problem. In this case, that aspect is that somehow leaves "draw" or suck up the water from the ground all the way up to themselves wherever they are on the plant - even if they are at the top of that huge tree.
There are two things we are going to inspect:

How high can you suck plain water (see the boy sucking on his long straw),
How high can you suck water with gas bubbles in it (that's what the girl is doing).

Starting materials

A bottle of water
An unopened bottle or can of soda pop (ginger ale might be best as it is the most fizzy)
Red, green or blue food coloring.
Measuring tape that is at least 50 ft long
A stairwell that is open for about 5 floors.
50 ft of clean, new, transparent tubing that is about 1/4 inch outside diameter and no more than 1/8 inch inside diameter. This is available in most hardware stores.
About 10 feet of twine (string)
Two assistants
Paper towels for cleanup
Record keeping equipment

sharpened pencil
small notebook
graph paper
camera and film (with close-up capability)

Methods

Step Directions and Diagram, if any
1 Ask permission to use the stairwell, and tell them what you will be doing. "We are testing one aspect of how trees might be getting water up to their top leaves - by some sort of suction. We need a very tall space, so our tube will hang down the stairwell, and we will be testing how high we can suck water up the tube. You can help us if you would like." (Notice how you have told about the significance of your work, and you have even offered to let them help and be part of science.)
2 You go to the top landing. Using the twine, tie a knot tightly around the tubing about 3 feet from the end, and tie the other end of the twine to the railing in front of you. You are doing this so that you cannot accidently drop the tubing all the way down to the bottom of the stairwell.
3 Lower the untied end of the tubing down to one of your assistants, who is standing at the bottom with the bottles of water and soda pop. It doesn't matter if the tubing hangs straight down. Some extra might coil on the floor at the bottom. Whole setup (top)
4 The bottom assistant then adds a few drops of food coloring to the water to make it more easily seen as the water rises in the tubing when you suck on it. The water is swirled to mix in the dye. Adding dye
5 The bottom assistant holds the end of the tubing into the colored water, and signals you to begin sucking. The assistant makes sure that the end NEVER comes out of the water! Tube in bottle
6 While you are sucking as hard as you can, the other assistant runs up the steps to stay even with rising column of colored water.
7 You keep sucking as hard as you can. It may help to stop up the end of the tubing with your tongue between breaths.
8 Finally, you can suck the water no higher, and your "middle" assistant will place a marker on the step closest to where the water level got. (Don't mark the tube as that can still be raised or lowered. You must have an "outside reference point"!) Marker on step Whole setup (bottom)
9 Later you will measure that height with your measuring tape. Release the tube from your mouth and let the colored water go back down. At a signal from the bottom assistant, give a little blow to push the remainder of the colored water out of the tube. Hopefully, you have selected an assistant who is intelligent enough to aim the end of the tubing into the bottle of colored water! Otherwise you might have a green or blue assistant, and a cleanup chore.
10 Next, your bottom assistant will pop open the bottle of soda pop, insert the end of the tube, and signal you to start sucking. Again, the middle assistant will run up the stairs following the rising soda pop. IMPORTANT: the middle assistant should watch closely to make sure that some of the carbonation is making bubbles in the tube. It should look like there are air spacers separating patches of liquid. After sucking as hard as you can, the middle assistant will place a marker on the soda pop's highest step. Bubbles in tube
11 Lower one end of the tape measure over the railing to measure the distances from the steps to the bottom (actually down to the top of the liquid in the bottles). This time it IS important that the tape be straight down!
12 For good science, you should do the preceeding two measurements several more times, and then average the results.
13 Contact THIS WEB SITE with your methods, if different than the above, AND your results.

OTHER THOUGHTS
Now comes the part of the project that will make you or break you in a science fair. More thinking is needed so that you will give a really good showing. Let's look at some things which you ought to think about and be ready to answer if your teacher or a science fair judge asks you.
14 You are asked:
"So what? What is the significance of this work you have done?" After reading an article (click this: on how water gets to the tops of tall trees, you will be able to respond to three of their fundamental conjectures:

Whether or not any air bubbles in the tubes prohibit sucking the water up
Whether or not leaves are able, under the laws of physics, to suck water up as high as 300 feet (your answer to "a" answers this)
Whether water has tensile strength (your answer to "a" answers this).

15 "Are you trying to tell me that you don't agree with more than a century of scientific thought?" My experimental data does not agree with what they have postulated, and I see nothing wrong with my methods or my data. Do you?
16 "What do you propose to do next? Are you going to do a follow up on this experiment?" Yes, I want to design an experiment on plants that have no leaves to see if they can transport water to their tops. That ought to show me whether my work is correct or not. If the leafless plants still move water up to their tops, then "leaf draw" cannot play a significant part in transpiration.

Step	Directions and Diagram, if any
1	Ask permission to use the stairwell, and tell them what you will be doing. "We are testing one aspect of how trees might be getting water up to their top leaves - by some sort of suction. We need a very tall space, so our tube will hang down the stairwell, and we will be testing how high we can suck water up the tube. You can help us if you would like." (Notice how you have told about the significance of your work, and you have even offered to let them help and be part of science.)
2	You go to the top landing. Using the twine, tie a knot tightly around the tubing about 3 feet from the end, and tie the other end of the twine to the railing in front of you. You are doing this so that you cannot accidently drop the tubing all the way down to the bottom of the stairwell.
3	Lower the untied end of the tubing down to one of your assistants, who is standing at the bottom with the bottles of water and soda pop. It doesn't matter if the tubing hangs straight down. Some extra might coil on the floor at the bottom.
4	The bottom assistant then adds a few drops of food coloring to the water to make it more easily seen as the water rises in the tubing when you suck on it. The water is swirled to mix in the dye.
5	The bottom assistant holds the end of the tubing into the colored water, and signals you to begin sucking. The assistant makes sure that the end NEVER comes out of the water!
6	While you are sucking as hard as you can, the other assistant runs up the steps to stay even with rising column of colored water.
7	You keep sucking as hard as you can. It may help to stop up the end of the tubing with your tongue between breaths.
8	Finally, you can suck the water no higher, and your "middle" assistant will place a marker on the step closest to where the water level got. (Don't mark the tube as that can still be raised or lowered. You must have an "outside reference point"!)
9	Later you will measure that height with your measuring tape. Release the tube from your mouth and let the colored water go back down. At a signal from the bottom assistant, give a little blow to push the remainder of the colored water out of the tube. Hopefully, you have selected an assistant who is intelligent enough to aim the end of the tubing into the bottle of colored water! Otherwise you might have a green or blue assistant, and a cleanup chore.
10	Next, your bottom assistant will pop open the bottle of soda pop, insert the end of the tube, and signal you to start sucking. Again, the middle assistant will run up the stairs following the rising soda pop. IMPORTANT: the middle assistant should watch closely to make sure that some of the carbonation is making bubbles in the tube. It should look like there are air spacers separating patches of liquid. After sucking as hard as you can, the middle assistant will place a marker on the soda pop's highest step.
11	Lower one end of the tape measure over the railing to measure the distances from the steps to the bottom (actually down to the top of the liquid in the bottles). This time it IS important that the tape be straight down!
12	For good science, you should do the preceeding two measurements several more times, and then average the results.
13	Contact THIS WEB SITE with your methods, if different than the above, AND your results.

OTHER THOUGHTS
Now comes the part of the project that will make you or break you in a science fair. More thinking is needed so that you will give a really good showing. Let's look at some things which you ought to think about and be ready to answer if your teacher or a science fair judge asks you.
14	You are asked: "So what? What is the significance of this work you have done?"	After reading an article (click this: on how water gets to the tops of tall trees, you will be able to respond to three of their fundamental conjectures: Whether or not any air bubbles in the tubes prohibit sucking the water up Whether or not leaves are able, under the laws of physics, to suck water up as high as 300 feet (your answer to "a" answers this) Whether water has tensile strength (your answer to "a" answers this).
15	"Are you trying to tell me that you don't agree with more than a century of scientific thought?"	My experimental data does not agree with what they have postulated, and I see nothing wrong with my methods or my data. Do you?
16	"What do you propose to do next? Are you going to do a follow up on this experiment?"	Yes, I want to design an experiment on plants that have no leaves to see if they can transport water to their tops. That ought to show me whether my work is correct or not. If the leafless plants still move water up to their tops, then "leaf draw" cannot play a significant part in transpiration.