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Welcome to Crash Course Kids. In this first episode, Sabrina looks at why all living things need to eat. Plus, she shows you how to investigate why all living things need to eat.

This first series is based on 5th-grade science. We're super excited and hope you enjoy Crash Course Kids!

///Standards Used in This Video///
5-PS3-1. Use models to describe that energy in animals’ food (used for body repair, growth, motion, and to maintain body warmth) was once energy from the sun.

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Executive Producers: John & Hank Green
Producer: Nicholas Jenkins
Cinematographer & Director: Michael Aranda
Editor: Nicholas Jenkins
Script Supervisor: Mickie Halpern
Writer & Consultant: Shelby Alinsky
Script Editor: Blake de Pastino

Thought Cafe Team:
Stephanie Bailis
Cody Brown
Suzanna Brusikiewicz
Jonathan Corbiere
Nick Counter
Kelsey Heinrichs
Jack Kenedy
Corey MacDonald
Tyler Sammy
Nikkie Stinchcombe
James Tuer

We all eat, right? But have you ever wondered why we eat?

I mean some animals only eat plants, others just eat other animals, and some creatures eat both plants and meat. But the thing is, all animals, including humans, eat.

And we don't just eat because we're hungry, or bored, or tired, or it tastes good. Although I could really go for a slice of pizza right now. We eat because we need food to live. More exactly, we need the energy that food gives our bodies to grow, move, and stay warm.

You've probably figure this out already from the things you've heard about how and when we eat. Like you've probably heard that breakfast is the most important meal of the day, or you might know that runners will "carb load" before a big race. But food is necessary for all living things, all the time.

You may have noticed that your collection of cool rocks that you have under your bed, never needs a lunch of club sandwiches and baby carrots. That's because they're nonliving things.

But food is most definitely a necessity for animals, and plants too. Even though we don't think of plants as "eating" because they don't have mouths, they still need food to grow and repair themselves, just like we do. In fact plants make a nifty model that can help us understand how the energy from food affects living things.

To see how food affects plants, we can test what happens when they get more or less food. Plants get most of their food from the sun, water, and carbon dioxide in the air. More on that another time.

But to test how food affects plants for yourself, you can use liquid plant food, that way you can control how much food or nutrients a plant gets.

So consider this little investigation.

Say you have two little plastic cups filled with potting soil, and you planted a lima bean seed in each one, then you give each plant a different amount of food. Plant number one would be your control, that means that you don't give it any additional food at all, just a little water and sunlight, and it'll do what plants do all on its own. Then you can make plant two your extra food plant. Ask your parents for some liquid plant fertilizer and add the recommended amount to plant two.

Now it you kept watering and feeding your plants the same amount for, say, four weeks, what do you think will happen? Would you expect both of the plants to grow the same amount? Or would one grow more than the other? If so, which ones?

Well, what you'd find is that plant two grew bigger than plant one because living things need food to give them energy, so they can repair themselves and stay healthy, and in this case, grow. So with more food, plant two got more energy, and that allowed it to grow bigger. Now go eat your vegetables.