Observations and results
When you put the flowers in the dyed water, did you see some of the flowers start to show spots of dye after two hours? Did you also see some dye in the stems? After 24 hours did the flowers overall have a colored hue to them? Did this hue become more pronounced, or darker, after 48 and 72 hours?
Water moves through the plant by means of capillary action. Specifically, the water is pulled through the stem and then makes its way up to the flower. After two hours of being in the dyed water, some flowers should have clearly showed dyed spots near the edges of their petals. The water that has been pulled up undergoes a process called transpiration, which is when the water from leaves and flower petals evaporates. However, the dye it brought along doesn't evaporate, and stays around to color the flower. The loss of water generates low water pressure in the leaves and petals, causing more colored water to be pulled through the stem. By 24 hours the flowers should have gained an overall dyed hue, which darkened a little over time. The stems should have also become slightly dyed in places, particularly where the leaves branch off.
More to explore
Plant Parts: What Do Different Plant Parts Do? from Missouri Botanical Garden
Capillary action from The U.S. Geological Survey, Water Science School
The Water Cycle: Transpiration from The USGS Water Science School
Transpiration in Plants from TutorVista.com
Suck It Up: Capillary Action of Water in Plants from Science Buddies
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4 Comments
Add CommentDear Scientific American,
Reply | Report Abuse | Link to thisI sincerely appreciate your effort to post an inquiry-based activity using plants. However, the explanation given here is wrong, and perpetuates a common misconception. Capillary action is not the force that moves water through a plant. If you put a straw into liquid, capillary action moves liquid a tiny, almost imperceptible distance up the straw, and it has a similarly negligible effect in plants. Sucking on a straw is a good analogy for water uptake into plants, as evaporation from the leaves draws water upwards - but this is not capillary action.
Here's a link to a lesson and an animation that accurately explain this topic http://tinyurl.com/cscc8fz. Here also is a summary of common misconceptions in plant biology, including the idea that capillary action is important http://www.actionbioscience.org/education/hershey.html/.
Good illuminating instructive article .
Reply | Report Abuse | Link to thisCapillary action IS the main cause of the rise of water in plant stems. The height of rise of water in a tube is inversely proportional to the diameter of the tube. In a very thin tube the water will rise an inch or more. In a microscopic sized tube such as in plant stems, the water can rise hundreds of feet. The rise of water when sucking on a straw is due to atmospheric pressure. Decrease the pressure above the liquid and atmospheric pressure from below will push the water up the straw. However, the highest that atmospheric pressure can raise water is 32 feet. At a height of 32 feet, the weight of the column of water equals atmospheric pressure and the column can not rise any higher. Thus this explanation can not account for water rising to the tops of trees taller than 32 feet. Put a piece of a paper towel in water and see that the water will rise several feet. At that point evaporation equals the rate of water rising through the towel and so the water reaches a maximal height. If you put the paper towel in a closed container, the water will go much higher. The FLOW of water through the plant depends on TRANSPIRATION. Flow of new water with nutrients depends on evaporation from the leaves to make room for new water molecules.
Reply | Report Abuse | Link to thisMaybe this video will help explain how a negative pressure model accounts for the movement of water up a tree. Please note between time 2:10 - 2:22 - it's not capillary action.
Reply | Report Abuse | Link to thishttp://www.youtube.com/watch?feature=player_embedded&v=BickMFHAZR0#!