WEBVTT

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- [Instructor] When you look at

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a rainforest ecosystem like this,

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one of the obvious questions may be,

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where do these plants come from?

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How do they grow?

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They're growing all the time,

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they're getting larger
and larger and larger.

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Where does that mass, where
does that matter come from?

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Pause this video and think about that.

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Well, you might already be
guessing where it comes from.

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It might have something
to do with photosynthesis,

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which we go into a lot
of depth in other videos,

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but this is a process where
you have carbon dioxide

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from the air in conjunction with water

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that primarily is coming from the soil,

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and it uses energy from the sun

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so I'll just draw that in,

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these yellow squiggles
coming from the sun,

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in order to do two things.

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The plant is going to be building itself

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using the matter in the
carbon dioxide and the water

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while also expelling
oxygen as a byproduct.

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And this matter that the plant is able

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to take from its environment
with photosynthesis

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is used to both become
the structure of the plant

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and a store of energy
in the form of sugars.

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Now, animals like you and me,

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we get our energy by
then eating these plants.

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And how do we unlock that energy?

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Well, that's where this
oxygen is really useful.

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That's why we need to breathe oxygen

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because by breathing the oxygen,

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we can essentially do
photosynthesis in reverse,

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and we can break down this matter,

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these sugars, that we're
getting from plants.

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So all of this biomass is coming

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from essentially water from the soil

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and carbon dioxide,
and energy from the sun

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is used essentially put it together.

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There might be a few other nutrients

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that are also coming from the
environment, like the soil,

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but primarily the water
and the carbon dioxide.