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How much of a tree is ACTUALLY alive? - Video học tiếng Anh
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How much of a tree is ACTUALLY alive?
How much of a tree is ACTUALLY alive?
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- Trees like this one can live for literally thousands
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of years, but this tree has been almost entirely dead
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the whole time.
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Not dying or sick, actually dead,
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because all trees are mostly dead,
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and that's exactly why they're still standing.
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Let me explain.
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A tree trunk is layered like a sushi roll.
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There are different kinds of tissues from inside to out,
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but all the width of a tree trunk traces back to here.
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The only actively dividing cells in a tree trunk
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are in this one thin layer Here on the outside.
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This layer is less than 1% of a tree's volume,
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but it does most of the work of growing
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and keeping a tree alive.
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Just outside that vascular cambium is a thin layer
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of tubular cells that sends sugars
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from leaves down to the roots.
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When you carve your name in a tree,
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you're actually cutting through some
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of the only living tissue in the trunk.
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On the outside of this layer,
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the cells move outward
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and turn into bark,
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and all the outside bark is just dead cells.
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To create a tough, rugged armor against things
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like fire, pests, and water loss.
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Things like corks, cinnamon, that's bark.
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Cells on the inside of that vascular cambium
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are also destined
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to die in a really special and carefully programmed way.
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Cells here make a second cell wall
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and produce loads of a substance called lignin,
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which makes the cell wall tougher and tougher.
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Finally, as they die, they also hollow out.
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As that thin living layer grows out,
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these dead cells get squeezed to the middle of the trunk.
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This is why trees get those age rings.
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It's also why a spot on a trunk will always be
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the same height off the ground
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no matter how tall the tree gets.
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But without all this carefully programmed death,
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trees wouldn't be able to grow as tall
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as they do, chasing all that light for photosynthesis.
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Remember how those dead cells in the middle are hollow?
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They basically create a tight-knit bundle of straws
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that draws water up the tree.
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It's a tree's plumbing, called sapwood.
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The cells farthest toward the center.
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Over time, that heartwood doesn't even move water anymore.
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It's literally just totally dead structural support.
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And in some trees, the heartwood could be most of the trunk.
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Something about this adaptation seems strange
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until you realize it lets trees focus
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most of their energy on those cells
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that are up top doing all the photosynthesis
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rather than wasting energy
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keeping all of that structural support alive.
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They're kind of like the opposite of us.
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We have a thin dead layer, our skin,
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and we're full of living stuff.
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Trees have a thin living layer
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and they're full of dead stuff.
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Puts a whole new meaning on dead inside.
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Follow me for more cool science stories.
