Cork Cambium: Secondary Growth Roots Video Lecture - NEET

hello friends this video on anatomy of
flowering plants part 23 is brought to
you by exam feel calm no more fear from
exam talk about the next type of cambium
that is a corn cambium so this is again
a layer of meristematic tissue which
develops around the cortex region and
that is why it is called cork cambium
right so to meristematic layers
basically develops once in the vascular
region and the other one in the cortex
region you know what is cortex right the
endodermis and the parenchyma cells
together and small ants cortex so what
does it do it tries to replace the
broken epidermis during the secondary
growth as I said wherever secondary
growth takes place more and more
secondary xylem is formed as a result
the secondary phloem and the primary
phloem gets destroyed so the epidermis
layers also get broken
so all that outer layers get broken so
there has to be something which will
replace the broken epidermis because if
epidermis is not there there is no
protection correct so for that purpose a
meristematic tissue develops in the
cortex region until give rise to new
cells which will be a replacement to the
epidermis layer now again this layer
also can form sense on the outer side as
well as on the inner side so here so
this is cork I'm sorry this is called
cambium this black line which you see
now this can again give rise to new
cells on the outer side as well as on
the inner side so on the outer side it
forms cork these new cells on the outer
side forms called and the cells on the
inner side gives rise to secondary
cortex
now the squark is also known
as another term which is often used for
caught is felon and another term which
is often used for secondary audits is
fellow dome so what is the secondary
partek secondary cortex is nothing but
it is made up of parenchyma cells so now
you see considering both the vascular
cambium and quad Kamri of the thickness
of the stem has increased so much so
basically this was vascular cambium
right this layer was vascular cambium so
vascular cambium give rise to secondary
xylem here and secondary phloem here
correct and this vascular cambium give
rise to secondary xylem here and
secondary phloem here now again outside
when Cod can be intimidating the cortex
here and Cod here
so the thickness is keep on increasing
so earlier when we started with it was
only a primary xylem primary phloem then
it became primary xylem primary so I'll
just write it which will help you to
understand how the thickness increases
thickness is basically this
cross-section right now when this
diameter keeps on increasing one will
added the circumference keeps on
increasing that means the thickness is
basically increasing so when we started
with there was only one primary xylem
and primary fluid that's all then we had
chimeras Island cambium and then primary
phloem then we have primary xylem
secondary xylem cambium then secondary
phloem and then flowing then even after
we had start against primary xylem and
secondary xylem then vascular cambium
then secondary phloem then primary
phloem outside that
we had the secondary cortex then cork
cambium and the outermost is cork so the
number of layers kept on increasing and
as a result the width of the stem keeps
on increasing and this is known as
secondary growth right okay I am home
saying the concept of secondary growth
is clear now now this secondary growth
is observed not only in stems but also
in roots in roots also we similarly have
a vascular cambium a cork cambium and
the concept still remains the same it is
just that the structure of the root is
ittle different right like when you
compare a daikon stem and the dicot root
their structure is little different so
because the pattern of the vascular
bundles are different in both of them so
there it is 8 here here it was conjoint
so those differences will be there but
otherwise the concept of secondary
growth will remain the same now talking
about quad cambium we often use a term
bark what is bar 2 bar is nothing but
all tissues exterior to the vascular
cambium therefore including the
secondary phloem anything that is
outside the vascular cambium so just now
I was telling right inside you have
primary xylem then secondary xylem then
vascular cambium then you have secondary
phloem then primary phloem and then you
have secondary cortex then you have quad
cambium and then you have the outermost
layer that is cork so where was vascular
cambium this was vascular cambium so
anything outside this is termed as bark
you often would have heard about the
bark off the tree cut the bark of the
tree so bark is nothing but this entire
outermost layer which we see that is
back
so the xylem is very much protected to
deep inside the stem cell layer so what
are the same layers that
stitute the bag it consists of secondary
phloem paedo and what is peridot peridot
is nothing but cork plus cork cambium
plus secondary cortex all of them
together is given the term peridot so
secondary phloem and peridot together
constitute the back so now that we have
understood the concept of cambium let us
quickly have a look at the vascular and
cork cambium together so now you
remember I told you that I will explain
this figure towards the end of the
lesson when I have covered everything so
now is the right time so look at the
first figure here we just have the pith
primary xylem primary phloem and
vascular cambium which is three
important layers are there but with time
what happens this vascular cambium gives
rise to new cells by cell division on
both inner side and outer side so inner
side it forms secondary xylem outer side
it forms secondary phloem and earlier it
already had primary xylem primary phloem
and vascular cambium so now the width
increases due to these two additional
layers secondary xylem and secondary
phloem now the amount of secondary zeig
and started increasing drastically
therefore the secondary phloem and the
primary before you started breaking down
the epidermis also started breaking down
so to compensate for that early another
year came up that is the cork cambium
so-called ambience is present in the
cortex region so now what happened this
cork cambium again gave rise to the
quark the Perry dome secondary cortex so
now because of the size variation in the
quad cambium
there was further increase in the girth
or in the width right so that is why you
see initially this was the thickness
then later due to the activity of
vascular cambium the thickness increases
again due to the activity of all cambium
the thickness further increases so this
is how secondary growth takes place in
plants right so I hope the secondary
growth in stem is very much clearer now
now in a very similar way secondary
growth also happens in root as I said it
is only that the inside xylem phloem
arrangement is little different so here
you can see this is the xylem this is
the flow in the red colored structure
Asylum and these green structures are
flowing their radial arrangement one
xylem one throwing one xylem one flight
right so this is your xylem and phloem
in between you have the vascular cambium
right so this vascular cambium will form
primary secondary xylem inside and
secondary phloem
outside so this secondary xylem and
secondary phloem are additional layers
because of which the thickness increases
after this what happens the cork cambium
is formed and all cambium will again
form a core outside and a secondary
cortex inside so basically this step
remains the same it is just that the
structure of the dicot root is little
different from the die cut step so thank
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