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Plants! We absolutely depend on them. Oxygen, food, and looking super nice to boot! But, plants have a lot more going on than meets the eye. How do we know that? Investigations and Experimentations!

Watch More Crash Course Kids: https://www.youtube.com/user/crashcoursekids

///Standards Used in This Video///
5-LS1-1. Support an argument that plants get the materials they need for growth chiefly from air and water. [Clarification Statement: Emphasis is on the idea that plant matter comes mostly from air and water, not from the soil.]

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Credits...
Producer & Editor: Nicholas Jenkins
Cinematographer & Director: Michael Aranda
Host: Sabrina Cruz
Script Supervisor: Mickie Halpern
Writer: Jen Szymanski

Executive Producers: John & Hank Green
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
Adam Winnik
(Intro)

Sabrina: Humans absolutely depend on plants. I mean, they provide a lot of the oxygen that we breathe, they're a huge part of our diet, and they sure do brighten up a room. I say we should thank them. (whispers) Thank you. (Normal voice) Thank you, friend.

It's too bad that plants don't talk because, I have a lot of questions for them. And you just don't find too many Ents around. But humans do know a whole lot about plants.

We know what resources they need to stay alive and how they make energy through photosynthesis. And plants didn't tell us these things. So how do we study plants?

You already know how scientists try and answer questions about the world around us. After all, as scientists ourselves, we've done activities to answer questions about plants, like: 'How do plants change light energy into chemical energy?' and 'Do plants really need dirt to grow?'

Each time we asked a question, we followed it with an investigation, a sort of exercise to try and find an answer to that question. Scientist do a lot of investigations about plants, and usually they follow the same general set of steps.

You probably already realized that investigations start with a question, and scientists sometimes have a pretty good guess about what the answer to the question might be. But a guess isn't good enough.

So they design an investigation to see if their guess is right. Investigations can be complicated experiments, or, they can be based on simple observations.

Then scientists look at the results of their investigations for evidence and then decide if the evidence supports their guess or not. Sometimes they don't find an answer to their question at all. In which case, it's back to the drawing board.

But sometimes, they do. For example!: Some scientists study special carnivorous plants, like the funky Venus flytrap. This plant noshes on insects on part of its diet, closing its leaves when it feels an insect walking over it.

But a few scientists noticed that a flytrap's leaves will close when an insect walked over them, but not when rain falls on them. What's up with that?

So, the scientists basically said: 'Investigation challenge, accepted'. it began with that basic question: 'How does the Venus flytrap feel insects on its leaves?'

Each scientist designed their own investigation and looked at the results for evidence. And like all good, mature humans, scientists share. So they shared their results with each other. And working together, learned an answer to their question.

They discovered that there are hairs inside each Venus flytrap leaf, and these hairs have to be jiggled a few times in a row, so that the leaf will close. A squirmy insect will cause the leaf to close, a drop of rain, not so much. Ding. Question answered!

Now, I wonder if we could do our own investigation about a plant's sense. We know that plants need sunlight for photosynthesis, you may have noticed that plants growing on a windowsill bend towards the light. Which is cool. But, how do they do it?

A scientist named Charles Darwin asked this exact question, and did an investigation of his own in an attempt to answer it. It went down a little something like this:

Darwin guessed that there was something in the tip of a plant's stem that helped it sense where the light was coming from. So he designed an experiment to see if he was right.

He grew plants, all the same type, and gave them all the same amount of light and water. He left one plant alone, he cut the tip from another, he covered the tip of one plant with a little glass cap, he covered the tip of another with a dark cap, and he covered the middle part of another plant with a dark piece of material.

He observed that as the plants grew, that one that had no tip and the one that had the dark cap didn't grow toward the light. So, he concluded that the evidence showed that he was right about the plant's stem tips sensing the light.

Investigations, for the win!

Because of studies like this it may seem like we know a lot about plants. But believe me people, there are even more things we don't know about them.

For one thing, scientists know that plants can communicate with one another, but don't know all the way 'how'. And scientists are always trying to figure out how to stop disease in plants, especially in the ones we eat.

So, scientists do activities called investigations that try to answer questions. Many of the investigations they've done helped us to learn a lot about plants, including how they can sense the world around them. And who knows what other investigations might discover some day.

So get out there, scientists and start investigating! But, not on your family's house plants. They probably want those to stay the way they are.

(Outro)