The plant needs water and minerals which are absorbed through the roots. There are tubes in the roots, stem and leaves that are responsible for carrying water. These are called xylem.
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| Hitting a xylophone with water tube to remember xylem carries the water! |
The plant makes its food (glucose) in the leaves and needs to transport it other parts of the plant. To transport food the plant uses a different set of tubes called phloem.
(I think phloem for phood- yes I know you spell it food, but I know you'll remember how to spell food!) Check out this student drawing of the process.
Today we looked at the xylem tubes in celery. After putting the plant in colored water for an hour, we could see the color travel up the stem into the leaves.
We even took a xylem tube out for further exploration.
Plants are able to transport water because water has some special properties. It is a polar molecule! This creates surface tension caused by adhesion and cohesion. Adhesion is water sticking slightly to other objects, like your finger (seeming to defy gravity.)
Cohesion is when water sticks to itself (try playing with a few drops on wax paper.) Or check out this "skin" created on top of a graduated cylinder.
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This causes capillary action, that is the tendency of water to rise in a small tube. The water sticks to the tube and the molecules stick to each other.
When the plant is losing water through the leaves during photosynthesis, more water is pulled up from the roots in the xylem tubes using capillary action.
We mad a model plant to show the pull of water. The capillary action moved the water up the "plant" and through the "leaf" (also separating the color black we put on the coffee filter "leaf.")
Check out a virtual transpiration lab on your own from Glenco/McGraw Hill.
virtual lab
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