Tropic & Nastic Movements - Biology Control & Co-ordination, Science Class 10 Video Lecture

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okay so let us start with the plant's
growth dependent movements growth
dependent movement of a plant in
response to a stimulus is termed as
tropic movement so this kind of movement
switch happens because the plant is
growing now as I said these movements
are also of different types based on
what kind of stimulus is there right so
these such growth dependent movements
are generally directional for example
you would have seen that the roots
always grow downwards
the chute always goes upward so that
means there is a particular direction
which they follow should never comes
down a root never goes up so these kind
of movements are generally Direction
they follow a particular direction now
such movements also happen due to a
stimulus because there has to be a
trigger for anything to happen I mean
why is the chute growing upward there
has to be a reason why is the root
growing downwards again there has to be
a reason so that reason behind these
kind of that directional movement is
nothing but the stimulus so these tropic
movements are divided into many types
depending upon the different types of
stimulus so tropic movements are also
known as tropism that is another word
for tropic movement so let us look at
the different types of tropic movements
phototropism geotropism hydro tropism
and chemo tourism so phototropism means
the plant movement which is growth
related in response to light the word
photo means light
similarly geotropism means geo means
earth earth or we can take it as a
gravity so the growth related movement
in a plant in response to
gravity then we have hydro dropped ISM
hydro is water so that is the movement
with in response to water and chemo to
autism and spot chemicals so these are
the different types of traffic movements
seen in plants so let us discuss each of
them in detail one by one so we will
start with phototropism it is bending of
a plant in response to light now it is
seen that in presence of light coming in
one direction like little suppose if
there is unidirectional line that means
light is coming only in one direction it
is seen that a plant tends to bend
towards life that is the shoot of the
plant
generally have a tendency to bend
towards the direction of light let us
look at this example now this tree in
this tree the light is equivalent on all
the directions I mean all the portions
of the plant are getting equal amount of
light so there is no bending but let us
if we look at some scenarios where it is
opposed if you have a plant plotted in
your balcony and it is potted in such a
way that one portion of the plant is
under shade and the other portion is on
that is getting the sunlight so you will
see that in your course of time the
plant gradually tends to bend towards
the light so the plant parts which bend
towards light are said to be positively
phototropic which part of the plant is
positively phototropic shoots because
the shoots bend towards light so shoots
are coiled positively phototrophic
whereas the plant parts which bend away
from light have said to be negatively
phototropic so roots are negatively
phototrophic because the direction of
light light comes from up red and the
roots grow downwards the roots are
basically going opposite to the
direction of light that is why roots are
negatively phototropic now if you want
you can perform this experiment to see
that yeah this
phenomenon actually happens let us
suppose if you have a plant this way the
plant is kept inside your house ok and
there it is kept in front of our window
and the light comes only from that
window so now what happens if you look
at this plant this portion of the plant
this side of the plant is shady here you
are not getting any light so light is
coming only from this direction so in
due course of time you will see that the
chute actually bends towards the
direction of light and the roots
gradually go away from the direction of
light so that is why shoots are
positively phototropic and rules and
they get deeply phototrophic now there
is a reason behind why these kind of
bending happens right so we will talk
about that reason a little length later
because plant hormone plays a role in
that so for now you should just
understand the different types of plant
movements right so let us look at the
next movement that is geotropism it is
bending of a plant in response to
gravity so plant parts which bent
towards gravity when I say gravity
gravity is nothing but earth
so those grandpa clouds which bend
towards gravity which grow towards
gravity they are called positively
cheered rocket so can you guess which
part of the plant is positively Geo
tropic yes you are right these are the
roots because roots grow towards the
surface of the earth it goes towards the
earth that is why it is towards gravity
and it is positively geo tropic whereas
plant parts which bend away from gravity
they are said to be negatively geo
tropic and the best examples are shoes
so here you can see the chutes always
grow upward and roots always grow
downwards that is why we told that these
growth related movements are directional
so here you see there is a particular
direction of the growth of shoes
similarly in phototropism also the shoes
are binding
towards the direction of
so that was also a directional movement
so the movement will happen only in one
direction it is not that one shoot will
bend towards like the other shoot will
Bend away from light so everything will
happen in one particular direction so
here if you see if you keep a plants
like this and if you keep it upside down
even then it is not that the roots will
grow straight like this the roots will
always try to go towards the Earth's
surface so this is how the roots will
start growing and this is how the stem
will start to grow so this is their
directional movement the third one is
hydro drop ISM which is the bending of a
light in response to water so there is
similarly plant parts which bends
towards water are positively hydro
tropic to which part then towards water
now soil contains water right so which
part of the plant grows towards soil
roots of course
so roots are positively geo tropic
because it is bending in a direction
where there is no water so roots are
positively G hydral cropping whereas
plant parts which Bend away from water
are negatively hydro tropic so shoots
are negatively hydro tropic because they
move their direction of movement is away
from the soil right so here let us
suppose if this is the soil so here you
have water so roots are going towards
water so they are positively hydro
tropic and shoots are going away from
water so they are negatively hydro
tropic so let us look at the next topic
movement that is he would drop ISM it is
the movement for plant in response to
chemicals so what do you think where do
we have the chemicals the chemicals are
again present in the soil itself so the
plant parts which bends towards
chemicals they are positively chemo
dropping now roots are positively chemo
tropic towards useful mineral
and everything is chemical right so in
the soil you have some useful chemicals
useful minerals but at the same time you
have some harmful chemicals so we can
say that rooms are positively cave or
topic that means it's tries to grow
towards the useful chemicals towards the
useful minerals like phosphorus nitrogen
all those things and it is negatively
chemo tropic towards the harmful acids
so acids are also chemicals and minerals
are also chemicals so if it grows
towards them then it is positively chemo
tropic if it goes away from them
then it is negatively chemo chocolate
right so these are some of the tropic
movements which are related to growth of
the plant so if you see all these tropic
movements happen only when the plants
actually grow so they are related to the
growth of the plant now let us look at
some of the nastic plant movements which
are not related to their growth they are
a result of immediate response to
stimulus so random plant movements in
immediate response to stimulus let us
look at some examples like creepers and
touch me not plant so here in this
picture you can see a creeper that is by
means of some soft stem like structure
their stems are not very hard so here
you see the green pellet structure they
are actually winding up with the grill
and then they are growing like that so
these soft stems are known as tendrils
so by means of the tendrils they come in
contact with some support may be a wall
or a building or a gate etc and that
part of the tender is in contact with
the object doesn't grow much grow as
fast as the other part as a result the
tent will tend to n circle the object so
here if you see let us suppose if this
is a tendon right so this portion of the
tendon is in direct touch with the one
and this portion is away now the portion
which is in direct touch with the grille
or with the object that does not grow
much whereas the other part grows more
so what will happen when one part
doesn't grow in the other
grows more there will be slight bending
and because of that bending they will
start moving in this fashion they will
start encircling that object so they
will start moving in this fashion so
this is also to some extent we can say
that this is also a movement which is
related to growth but here it is not
very specific in direction it is not a
directional movement for example in case
of phototropism or in case of geotropism
the shoes will always go up roots will
always go down in this case it is not
like that it will take the direction of
that particular object over which it is
growing similarly let us take the
example of the touch-me-not grant which
belongs to the mimosa family so these
kind of plants if you see here when you
touch these plants this is how the
leaves respond so as soon as you touch
them they leave start getting assemble I
mean they start drooping up so this kind
of movement is not related to growth and
it is also an very immediate response to
the stimulus the stimulus here is the
touch and what is the response the
response here is the folding of the
needs right so why does this happen how
does this response come into picture
now this response is immediate here and
often this is known as thick motor
opposite which means response to touch
like how we have chemo crop ISM response
to chemicals similarly people also give
a turn on thigmotropism which is
response to touch now why does this
happen this happens because of the
change in the turgor pressure what is
trip target pressure now when you look
at the structure of a touch-me-not plant
it is somewhat like this you have these
kind of leaves so in the picture also
you can see they have these kind of
leaves right
now this opening and closing is governed
by some fluid-filled structures which
are present at the base of each leaflet
now in one this this one leaf this one
big leaf is a compound leaf and in one
leaf you have small leaflets so each of
this is called a leaflet now at the base
of each leaflet there is a structure
which is a fluid-filled structure which
is known as pile Venus so we have a
fluid-filled structure which is known as
pile Venus so it is present at the base
of each leaflet it is also present at
the base of the compound leaf and it is
also present at the base of the leaf
stock that means let us suppose if this
is the plant so somewhere here you again
have another leaf like this so somewhere
here you again have another pail Venus
so we call this as primary pile - we
call this as secondary pulvinus
and we call this as tertiary pile winner
so this is called primary pile - which
is present at the base of the leaf stock
now the pile Venus which is present at
the base of the compound leaf that is
called secondary pile venus and the
puffiness which is present at the base
of each leaflet that is called
tertiary pulvinus and what does pile
Venus it is nothing but a fluid-filled
swollen structure right now what happens
is that when we touch the leaf let's
that is why we when the set when the
leaf is patched those cells produce some
electrical signals and those cells in
the PAL Venus respond by flushing out
potassium and water now inside the pile
Venus I told it is fluid filled so the
cells inside the pile Venus has lot of
water so whenever it is touched so how
do they respond to that starch by
expelling out water now due to this
excessive loss of water then reflect
closes so basically turgor pressure
now I told it happens due to change
integral player it causes change in
Turgut pressure now water starter
pressure the other pressure is nothing
but the pressure that happens when water
inside the cell begins to expand and
push on the cell membrane I mean inside
the leaf we have small plant cells so
inside that we have water now when water
increases too much and then it exerts a
pressure on the cell membrane that is
known as turgor pressure now in the
amount of water inside the change varies
if the amount of water decreases then
what happens then leaflet will shrink if
the amount of water increases then it
will again expand right so it is all
about the change in the amount of water
now whenever it is touched what happens
is that the cells inside the pile Venus
they respond by expelling out excess
water
now when the water expands out there is
less water inside and as a result the
leaflets shrink so this is the reason
behind this drooping of the touch me not
plant right so these kind of movements
fall under the category of nastic
movements that is they are random
movements they are not directional
movements and they are an immediate
response to stimulus clear thank you
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