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Why do we need to hydrate? – Victor, 9, Ohio

Dear Victor,

Is there anything better than lapping up cool water on a hot day?

I talked about why we need to hydrate with my friend Ed Johnson. He teaches classes about the human body in the School of Biological Sciences at Washington State University.

It turns out that up to 60% of an adult human’s body is water. A kid’s body contains even more water than a grown up. When you were a baby, you were about 78% water.

Humans use that water for all kinds of things. It keeps you cool when you sweat. It removes waste when you pee. It moves important stuff around inside your body. It even cushions your brain and spinal cord.

But staying hydrated is really about your cells.

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Why do plants need water? – Emma, 9, New York

Dear Emma,

When I’m thirsty, I pick up a glass of water with my paws and drink it—just like you do. But plants don’t have paws or mouths, so how (and why) do they drink it?

To find the answer, I talked with my friend Helmut Kirchhoff. He’s a scientist at Washington State University. He studies plants and biochemistry.

He told me plants need water inside their cells. Water makes plant cells strong and flexible. It also dissolves stuff. That makes it possible for chemical reactions to happen inside plant cells—like the reactions a plant uses to make energy during photosynthesis. Plants also need water to move around nutrients and other molecules required for life.

“Water is essential for life, but plants must move nutrients from the soil to the leaves,” Kirchhoff said. “So, they have this very nice transport system called xylem. Xylem is an ancient Greek word that means wood. It works like a straw to move water and nutrients from the roots to the leaves.”

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How do plants that need very little water survive? – Alivia, 11, Maryland

Dear Alivia,

My neighbor has a very prickly garden. It’s full of cactuses—including one thorny plant nearly as tall as my house. That’s not something you see every day in the Pacific Northwest. Cactuses usually live in dry places like deserts.

I talked about your question with my friend Linda Chalker-Scott. She’s a garden scientist at Washington State University.

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How does it rain? — Gabby, 10, Ohio

Like most cats, I don’t love wet fur. I check a weather app every morning to see if I need an umbrella. But how rain happens was a mystery to me.

So, I talked about rain with my friend Nathan Santo Domingo. He’s a field meteorologist with AgWeatherNet of Washington State University. That’s a weather tool for farmers, gardeners and other people in Washington.

“The first thing to remember is that Earth's surface is 71% water,” Santo Domingo said. “We also have a giant orb in the sky—the sun—that’s feeding energy into the atmosphere and reaching down to Earth's surface.”

The sun’s energy changes the water in the oceans, rivers and lakes. The water changes from a liquid to a gas called water vapor. That water vapor floats up into the bubble of gas that surrounds Earth—called the atmosphere.

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Dr. Universe: How are sea animals affected by water pollution? - Natalia, 10, Florida

If you ever visit the beach, take a look at all the animals: crabs scuttling across the sand, seals bobbing on the waves and sea stars tucked into tide pools. Maybe there are even whales spouting on the horizon. Earth’s oceans are home to thousands of creatures. But, as you know, human pollution reaches our waterways and all the animals that live in them. To learn more, I talked to my friend Erica Crespi, an associate professor in the Washington State University School of Biological Sciences. Crespi studies how animals that live in water respond to all kinds of stresses, including pollution. Read More ...