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SCIENCE BEHIND: How water keeps plants alive

A mix of botany, chemistry and physics.

NORFOLK, Va. — Plants, like most living things, need water to survive.

"They use xylem and phloem. Xylem is what’s taking up the water and after a certain amount of time, we’ll see the colors start to change in the petals," said Alexandra Cantwell, the Adult Education Manager at the Norfolk Botanical Garden. 

She has a simple, at-home experiment to show how plants absorb the water they need to survive.

What you'll do is put the stems of white flowers or celery in water dyed with food coloring. You'll then watch how the xylem does its job of taking in the water and food coloring.

"That’s important because not only is it taking up water, you see it’s taking up whatever is in that water [like] nutrients, fertilizer."

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All the while, botany blends with forces from chemistry and physics: "Cohesion and surface tension are what hold the liquid together and adhesion is what attracts that liquid to another substance."

When those forces are stronger than gravity, they pull the water - and whatever is in it - through the xylem to disperse it through the plant. The water travels through the plant until it gets to the end, where transpiration occurs and the water evaporates out of the plant.

However, the food coloring can’t evaporate. It gets deposited where we see the colors left over.

This colorful illustration shows that the plants are not only working for their wellbeing but ours as well. 

"They’re cleaning up various things in the soil... toxins, pollutants. Things like that," Cantwell explained. "So they’re a key component to cleaning the water quality in the area."

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