00:00:00
plants and trees are not just great at
00:00:03
creating their own food from sunlight
00:00:06
but they are also excellent in moving
00:00:08
that food around when they have excess
00:00:11
of food
00:00:12
they move it to their storage organs for
00:00:14
example if this was a carrot or a potato
00:00:17
plant
00:00:18
then they would move that excess food
00:00:20
down so they move the excess food down
00:00:23
and store it for future
00:00:25
and now let's say maybe during the
00:00:27
winter season there isn't much sunlight
00:00:29
so they cannot photosynthesize so
00:00:31
they're not able to get a lot of food
00:00:33
now they can move this food up to
00:00:36
wherever they want
00:00:38
so they can move it back from the
00:00:40
storage organs to the place where they
00:00:42
need maybe the growing areas
00:00:44
and this process of moving the food
00:00:46
around wherever they want we give a name
00:00:48
to it we call it translocation
00:00:52
trans
00:00:54
location
00:00:56
this is basically plants and trees
00:00:58
moving the food around to the places
00:01:00
they need but the big question is how do
00:01:03
they do that
00:01:04
i mean for one how do they even
00:01:06
understand which part of the plant body
00:01:09
needs food because they don't have a
00:01:10
brain and secondly what mechanism do
00:01:13
they use to transport that food up or
00:01:15
down according to their needs
00:01:17
well let's find out
00:01:19
now before we continue let's back up a
00:01:22
little bit we've already seen in
00:01:23
previous videos that plants and trees
00:01:26
consist of
00:01:27
pipe-like structures to transport stuff
00:01:30
around
00:01:31
that starts from their roots all the way
00:01:32
to their leaves and we call these
00:01:34
structures vascular tissues
00:01:37
and there are two kinds xylem that
00:01:40
transports water and minerals from the
00:01:42
soil to the different parts of the body
00:01:45
and phloem which mostly transports food
00:01:48
now if these terms look new to you or
00:01:50
you need a refresher on this
00:01:52
then you can go back and watch our
00:01:53
previous videos on intro to vascular
00:01:55
tissues and videos on xylem and
00:01:58
transpiration
00:01:59
but if you feel comfortable then let's
00:02:01
continue
00:02:02
now in this video since you want to talk
00:02:04
about translocation meaning
00:02:06
transportation of food we are going to
00:02:08
be concentrating on phloem
00:02:12
so translocation happens inside the
00:02:15
phloem food gets transferred in phloem
00:02:18
but how
00:02:19
well let's see let me draw xylem and
00:02:21
phloem so let's say
00:02:23
this is the xylem tissue which has water
00:02:26
in it this is going to be important for
00:02:28
us as well
00:02:29
and here is our phloem
00:02:32
phloem mostly contains sugar molecules
00:02:35
dissolved in water forming a very thick
00:02:38
sugary sap which is food for them
00:02:41
and if you're wondering what these
00:02:42
things are over here at the sides that
00:02:45
is some leftover cytoplasm the cells
00:02:47
don't lose all of their cytoplasm and
00:02:49
similarly this is the cell walls
00:02:52
they have developed gaps in between so
00:02:54
they have not lost their cell walls like
00:02:55
in xylem some gap is developed so that
00:02:58
the food can this whole sap can move
00:03:00
throughout the phloem and if you're
00:03:02
wondering why it is structured like this
00:03:04
we'll talk a little bit about that
00:03:05
towards the end
00:03:07
anyways imagine a couple of cells next
00:03:09
to phloem
00:03:10
let's assume these are far apart okay
00:03:12
not so close
00:03:14
and let's assume this cell has a lot of
00:03:16
sugar molecules in it
00:03:19
and imagine this cell doesn't have much
00:03:20
sugar molecules it needs a lot let's say
00:03:22
it's one of the growing regions of this
00:03:24
plant so it needs a lot of sugars
00:03:26
so how do we transport the sugar from
00:03:28
here to here is the question
00:03:30
well you can kind of guess the process
00:03:32
we take some of the sugars
00:03:34
put it into the phloem
00:03:36
then we make sure it transports through
00:03:38
the phloem till here
00:03:40
and then we remove the sugar and put it
00:03:42
into the cell
00:03:45
that makes sense right but a couple of
00:03:47
questions could be
00:03:48
how does the phloem know
00:03:50
in which direction to transport this
00:03:52
food because that cell which is in need
00:03:54
of sugars can be anywhere it can be
00:03:56
below it or it can be above this as well
00:03:59
so how does it know whether it has to go
00:04:00
down or up
00:04:02
and secondly how do you even move this
00:04:04
thick sugary sap through the phloem
00:04:07
so let's put this back over here and
00:04:11
let's see how this works
00:04:13
so the first step as you predicted is to
00:04:15
put the sugar
00:04:16
into the floam tube i'm just going to
00:04:18
call that
00:04:19
loading
00:04:23
and this process is an active process
00:04:26
what does that mean
00:04:28
active
00:04:29
well think about it if the concentration
00:04:32
over here of sugars is less than over
00:04:34
here then sugars will automatically
00:04:36
diffuse from higher to lower
00:04:38
concentration but pretty soon the
00:04:39
concentration will equalize
00:04:41
how do you move even more sugars there
00:04:45
well that requires energy the cells have
00:04:48
to spend some energy to to you know move
00:04:51
the sugar from lower to higher
00:04:53
concentration
00:04:54
so
00:04:55
by using energy
00:04:58
the sugars need to be transported into
00:05:00
the phloem
00:05:01
and because energy is utilized for this
00:05:04
process we say it's an active process
00:05:08
now see what happens because of a lot of
00:05:10
sugar the concentration of sugar is much
00:05:13
higher in this region compared to any
00:05:15
other regions and remember nature always
00:05:17
likes to balance the concentration out
00:05:20
so one way to reduce the concentration
00:05:22
is to put this sugar back but remember
00:05:24
that's not possible we're not doing that
00:05:26
so what else can nature do
00:05:29
well there's xylem right next with a lot
00:05:31
of water so you know what's going to
00:05:33
happen
00:05:34
water will start flowing from xylem
00:05:37
into the phloem to this part of the
00:05:40
phloem
00:05:41
because of osmosis
00:05:43
so let me write that as step two
00:05:46
remember osmosis it's a process in which
00:05:48
solvent flows like water starts flowing
00:05:51
from a low concentration region to a
00:05:53
higher concentration region basically
00:05:55
water is flowing to try and dilute this
00:05:57
concentration
00:05:59
okay what does that do well because a
00:06:01
lot of water is flowing in this region
00:06:04
of the phloem starts puffing up over
00:06:06
there
00:06:08
this increases the pressure over here
00:06:11
and what i mean by that is you can
00:06:12
imagine this
00:06:14
these walls are pressing on this
00:06:17
solution squeezing that solution a lot
00:06:21
now what do you think will happen if i
00:06:23
squeeze this solution a lot
00:06:25
well it'll automatically start moving
00:06:28
from here
00:06:29
to a region where there is low pressure
00:06:32
it's kind of like squeezing a water
00:06:33
balloon and where do you think is the
00:06:35
pressure lower
00:06:36
the pressure is lower where there is
00:06:38
less sugar concentration right because
00:06:41
if there's less sugar concentration
00:06:42
there will be less water over here and
00:06:44
that's exactly where you need to send
00:06:47
your sugar molecules
00:06:49
so if
00:06:51
on the top there is a cell which has
00:06:52
very low sugar concentration
00:06:54
automatically that part will have low
00:06:56
pressure automatically the sap will move
00:06:58
up if it turns out that somewhere in the
00:07:00
bottom there is low concentration
00:07:02
automatically
00:07:03
the pressure over there will be very low
00:07:05
and the sap will move down
00:07:06
and this is how the pressure decides in
00:07:09
what direction the sap will move so in
00:07:13
our example the sap will move down
00:07:16
from here to here let's call that as our
00:07:18
step three
00:07:20
and we can call this the bulk flow
00:07:24
the bulk flow driven by pressure and the
00:07:27
reason we are calling it bulk flow is
00:07:29
because
00:07:31
this whole thing is a solution remember
00:07:32
even though i've put dots over here this
00:07:34
is one single solution and so the whole
00:07:38
whole solution moves down not just this
00:07:40
part
00:07:41
all right so let me show you what that
00:07:43
would look like so as the solution moves
00:07:45
this pressure is relieved let me get
00:07:47
that back to normal
00:07:49
and so due to the high pressure over
00:07:51
here this whole solution
00:07:54
will start moving like this the whole
00:07:56
thing will move from high pressure to
00:07:59
low pressure until it reaches over here
00:08:02
and then finally the sugar reaches the
00:08:04
low pressure region because there is
00:08:06
less concentration of sugar it will move
00:08:09
out of phloem
00:08:10
and it can now be taken up by this cell
00:08:14
and so this will call it as step four
00:08:16
unloading happens the sugars get
00:08:18
unloaded from the phloem tube
00:08:21
so let's unload that sugar from the
00:08:23
phloem
00:08:25
into the required cell
00:08:28
and finally remember that region which
00:08:30
had a lot of concentration of sugar had
00:08:32
a lot of water due to the osmosis well
00:08:35
now that concentration has lowered so
00:08:37
that water will move back
00:08:40
to xylem
00:08:41
so in step 5 again osmosis happens
00:08:45
and the water moves back
00:08:48
and that's how translocation happens
00:08:50
inside plants
00:08:52
now before we summarize and wind up this
00:08:54
video one question we need to address is
00:08:56
why phloem structure is a little
00:08:58
different than that of xylem why does it
00:09:00
have cytoplasm a little bit of cytoplasm
00:09:02
left why are the end walls not
00:09:03
completely gone like in the xylem
00:09:06
well that's because these cells
00:09:09
are alive
00:09:11
phloem has live cells
00:09:14
in contrast xylem has
00:09:16
dead cells
00:09:19
and so xylem cells can afford to lose
00:09:21
all of their stuff because they are dead
00:09:23
right but phloem cells need a little bit
00:09:25
of cytoplasm and their cell walls to
00:09:27
stay alive
00:09:28
now that could raise even more questions
00:09:30
first of all you may be wondering how
00:09:31
can cells stay alive without a nucleus
00:09:33
or without a mitochondria how can these
00:09:35
cells be alive
00:09:37
well in fact you know how they are
00:09:39
staying alive they have a partner cells
00:09:42
which i have not shown over here but
00:09:43
each cell is connected to a partner let
00:09:45
me show you what would that look like if
00:09:47
i were to draw those so these are the
00:09:50
partner cells and and they have all the
00:09:52
stuff needed to keep these cells alive
00:09:56
in fact they are life partners okay and
00:09:59
that's why these cells are called
00:10:01
companion cells all right and so in
00:10:04
reality if you're wondering uh when you
00:10:06
want to load the sugars you have to
00:10:08
first load it into the companion cell
00:10:10
and then it goes into the phloem
00:10:12
similarly while unloading it first goes
00:10:14
into the companion cell and then it goes
00:10:15
out of the flourium but that's a small
00:10:17
detail we don't have to worry too much
00:10:18
about that so let me get rid of those
00:10:21
so it's those companion cells that keep
00:10:23
them alive but another question you
00:10:25
might be wondering is why do we have to
00:10:26
go through all that trouble to keep
00:10:28
these cells alive why is why is it
00:10:30
necessary that these cells need to be
00:10:31
alive
00:10:33
well the answer is in this process you
00:10:36
see we just saw that in order to load
00:10:38
the sugar into the phloem that requires
00:10:40
energy it's an active process
00:10:43
and the cell can only generate energy if
00:10:46
it is alive
00:10:48
so if the cells were dead like in xylem
00:10:51
they wouldn't be able to generate energy
00:10:53
they wouldn't be able to load sugar they
00:10:54
wouldn't be able to accept that sugar
00:10:56
molecules it would just diffuse back and
00:10:58
then the phloem transfer wouldn't work
00:11:01
and xylem cells don't need to be alive
00:11:03
because the mechanism of xylem is only
00:11:05
based on physical forces like suction or
00:11:08
the pressure from the bottom from the
00:11:10
roots right you don't need the cell the
00:11:12
cells don't need to use any energy so
00:11:14
they can afford to be dead but phloem
00:11:16
needs to be alive
00:11:18
all right that's pretty much it so let's
00:11:20
quickly summarize what did we learn in
00:11:22
this video we saw that plants and trees
00:11:24
can move the food up or down based on
00:11:27
their requirement and we call this
00:11:29
translocation and this happens inside
00:11:31
the phloem tissues
00:11:33
and how do these sugars go from one
00:11:35
place to another
00:11:37
well in the first step we have loading
00:11:39
where the sugars get loaded actively
00:11:41
into
00:11:43
the phloem phloem tubes and this
00:11:45
requires energy that's why it's called
00:11:47
as an active process and that's why
00:11:49
these cells need to stay alive and in
00:11:51
doing so because the concentration over
00:11:53
here has increased
00:11:55
water starts flowing from xylem into the
00:11:58
phloem to try and decrease that
00:11:59
concentration due to osmosis and because
00:12:02
of that a lot of water comes in and the
00:12:04
cell now
00:12:05
kind of over there puffs up
00:12:07
i like to imagine that way because now
00:12:09
you can see that there's a lot of
00:12:10
pressure over there
00:12:12
and then because there is high pressure
00:12:14
region over here it automatically wants
00:12:16
to move towards the low pressure region
00:12:18
and the low pressure region is the
00:12:19
region where there is less concentration
00:12:21
of sugars
00:12:23
and as a result the whole sap starts
00:12:25
moving towards the low concentration
00:12:26
region
00:12:28
and so this is that step three which is
00:12:30
a bulk flow it starts moving the whole
00:12:32
sap moves
00:12:33
from higher to lower concentration and
00:12:36
now that that pressure is relieved
00:12:40
and then in step four the sugars
00:12:43
automatically diffuse out because
00:12:44
outside there is less concentration and
00:12:46
that can now be taken up by the cell
00:12:49
which we will call as
00:12:50
unloading and then finally the excess
00:12:53
water drains back into the xylem because
00:12:56
the concentration has decreased so it
00:12:57
goes back and that's how translocation
00:13:01
works in plants and trees
