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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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0:00
- Trees like this one can live for literally thousands
0:03
of years, but this tree has been almost entirely dead
0:06
the whole time.
0:07
Not dying or sick, actually dead,
0:09
because all trees are mostly dead,
0:11
and that's exactly why they're still standing.
0:13
Let me explain.
0:14
A tree trunk is layered like a sushi roll.
0:16
There are different kinds of tissues from inside to out,
0:18
but all the width of a tree trunk traces back to here.
0:20
The only actively dividing cells in a tree trunk
0:23
are in this one thin layer Here on the outside.
0:25
This layer is less than 1% of a tree's volume,
0:27
but it does most of the work of growing
0:29
and keeping a tree alive.
0:30
Just outside that vascular cambium is a thin layer
0:33
of tubular cells that sends sugars
0:34
from leaves down to the roots.
0:36
When you carve your name in a tree,
0:37
you're actually cutting through some
0:39
of the only living tissue in the trunk.
0:41
On the outside of this layer,
0:42
the cells move outward
0:43
and turn into bark,
0:44
and all the outside bark is just dead cells.
0:48
To create a tough, rugged armor against things
0:50
like fire, pests, and water loss.
0:51
Things like corks, cinnamon, that's bark.
0:54
Cells on the inside of that vascular cambium
0:56
are also destined
0:57
to die in a really special and carefully programmed way.
1:00
Cells here make a second cell wall
1:02
and produce loads of a substance called lignin,
1:05
which makes the cell wall tougher and tougher.
1:06
Finally, as they die, they also hollow out.
1:09
As that thin living layer grows out,
1:11
these dead cells get squeezed to the middle of the trunk.
1:14
This is why trees get those age rings.
1:17
It's also why a spot on a trunk will always be
1:19
the same height off the ground
1:20
no matter how tall the tree gets.
1:22
But without all this carefully programmed death,
1:24
trees wouldn't be able to grow as tall
1:25
as they do, chasing all that light for photosynthesis.
1:28
Remember how those dead cells in the middle are hollow?
1:30
They basically create a tight-knit bundle of straws
1:32
that draws water up the tree.
1:33
It's a tree's plumbing, called sapwood.
1:36
The cells farthest toward the center.
1:37
Over time, that heartwood doesn't even move water anymore.
1:41
It's literally just totally dead structural support.
1:43
And in some trees, the heartwood could be most of the trunk.
1:46
Something about this adaptation seems strange
1:48
until you realize it lets trees focus
1:50
most of their energy on those cells
1:51
that are up top doing all the photosynthesis
1:53
rather than wasting energy
1:55
keeping all of that structural support alive.
1:57
They're kind of like the opposite of us.
1:58
We have a thin dead layer, our skin,
2:01
and we're full of living stuff.
2:02
Trees have a thin living layer
2:04
and they're full of dead stuff.
2:05
Puts a whole new meaning on dead inside.
2:07
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