now in a previous video I showed you
that you can only suck up a straw that's
ten point three meters long and that's
even if you can create a perfect vacuum
inside your mouth if you haven't seen
the original video check it out but that
raises an interesting question which is
how can these trees which are a hundred
meters high get the water all the way
from their roots up to the leaves the
arguments is you're alluding to is that
if you're sucking water up through a
drinking straw for example you can only
have a straw thirty-three feet long the
reason for this height limit is because
the weight of the water in a column must
be supported by the pressure difference
between the top and the bottom so the
bottom you're gonna have atmospheric
pressure and the lowest pressure you can
produce at the top would be a vacuum
that is zero pressure so atmospheric
pressure can support a column of water
that is only ten meters high what's
worse is if you were able to create a
vacuum the water would start boiling
spontaneously that's called cavitation
and obviously that can't be taking place
within a tree so how are they doing it
well we started to develop some
different theories my guess those people
talked about this being continuous water
column and what they I think when when
you say that you think this is big like
empty pipe right that's what we're
picturing but I think what's more likely
to be the truth this big tube which
you're saying needs to be filled with
water it's actually made up of cells the
tree effectively has vowels in it so you
don't have a column of water that is
much higher than thirty-three feet or
less so that the water is pumped up by
osmotic pressure due to differences in
concentrations of sugars and so on but
each individual stage is just quite a
small one my guess is that it's probably
more like a bucket brigade where once
you know here at the end there's
sunlight coming in and then heat up the
water in the water evaporates and so the
water goes off as water vapory pay price
up week now this guy's like my buckets
empty I want some more water and this is
a so this is a cell here
but though this one can give the water
there because locally like it's
surrounded by water it's a little bit of
water will go there but by osmotic
pressure now another theory is that
osmotic pressure at the base could
actually push the water all the way up
the tree if the solute concentration is
different enough between the roots and
the water and the surrounding soil then
water would actually want to push into
the roots in order to equalize the
solute concentrations that could create
a positive pressure which would push the
water up the tree and this hypothesis
led me to being challenged to blow water
up a tube now the water as you can see
is veritasium color now my ability to
blow water up that tube was impressive
but I don't really think that a tree
would be able to get so much osmotic
pressure at the roots that it could push
the water up a hundred meters well some
people may be wondering why we haven't
talked about capillary action yet that's
due to the adhesion between the water
molecules and the walls of a tube so you
can suck water up through perforated
materials now I'm not sure that the
tubes inside a tree are small enough for
this effect to have a significant impact
but it may well I don't want to give you
the complete answer yet I'd like you
guys to tell me what you think and maybe
post a video response I'll tell you that
I had a significant misconception that
was stopping me from working this out so
if you can spot what that is do let me
know and let me give you a summary of
the ideas we came up with one that the
tree does not contain a continuous water
column number two
osmotic pressure at the roots may be
pushing the water up the tree number
three osmotic pressure throughout the
tree helps pull the water up and number
four capillary action so let me know
what roles you think those different
factors play in allowing a tree to draw
the water up 100 meters and if you don't
want to do that work then subscribe to
the channel and I'll post the answer in
a week