ShmoopTube

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[Coop and Dino singing]

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So we all know about water. [People swimming in a pool]

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And if you don't then…wow. That's an impressive thing to not know about.

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Quick refresher: it's that wet stuff you can drink and swim in?

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Just…usually not at the same time….

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Well water is also used by humans to transport stuff. [Man pushes cargo onto ship]

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Like cargo...

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And cruise ships...

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…and very relaxed people sitting awkwardly in donut-shaped floating devices. [People floating in the water on dingys]

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But in the case of plant stems, it's the plants doing the moving – and what are they moving?

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Water. In a plant stem, the transportation of fluid [Arrows showing transport of water]

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throughout the plant is handled by the xylem and phloem.

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Put those two together and you get…a great musical instrument! …well…almost. [Person playing the xylophone]

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The xylem's job is to move the water up the plant from the root, into the shoot.

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But seeing as plants don't have pumps like a heart to move all that liquid around...

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…the water moves through the plant using what's called a “transpiration stream,” [Arrows moving through the plant]

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which involves vessels in the xylem. Water moving upwards against gravity without

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a pump. Sounds a bit like magic, huh? [Magician on stage as water travels up through a plant]

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Well, it all happens because of something called “capillary action.”

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This works because water molecules are charged, meaning they're basically like a group of

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BFFs – they love to stick together.

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Now think of the solids on the inside of a plant stem as a super-cool birthday party [A disco with people dancing]

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that these water molecule besties really want to get invited to.

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Water is attracted to the very center solids of the stem, which is what draws it upwards.

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This is capillary action, and it's what keeps the water crawling upwards along the xylem [Arrow pointing to capillary action of water molecules]

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and against the force of gravity. And when the stomata open up to let in carbon

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dioxide to be used for photosynthesis, some of this water moves out of plant and into the air.

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This happens because the plant has more water inside of it than outside in the surrounding

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air, so it decides to share. [Water molecules travelling around the plant]

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How nice. Someone raised that plant right!

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When this water evaporates out of the stomata, new water molecules are pulled into the stem, [Water evaporating from plant]

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going all the way through the root.

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Think of it like the line up outside of a club. When some party-goers leave, the bouncer

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lets in new ones from the front of the line. [Bouncer lets water molecules into a party]

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This entire process keeps the water molecules moving and the plant a-planting.

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Let's just hope the molecules in line are dressed appropriately.

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