Plants respond to environmental stimuli like light and gravity through slow, hormone-driven growth adjustments, primarily controlled by auxins, to ensure survival and optimal resource acquisition.
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in today's video we're going to take a
look at how plants can respond to their environment
environment
and in particular we'll look at the role
now just like animals plants have to be
able to respond to stimuli in their
environment in order to survive
they just do it much more slowly than
animals do
for example they can sense light and
grow their shoots towards it to maximize photosynthesis
photosynthesis
they can sense gravity
so that they can grow their roots
downwards to fix themselves into the
soil and find more water and minerals
and some plants can even sense touch
so that they can climb around other objects
in order to do all of this stuff
plants have to rely entirely on hormones
they don't have any nervous system like
animals do
and the hormones that they do have
normally act locally
rather than flowing around the entire
organism like they would in animals
one group of these plant hormones are
the auxins
which control growth are the ends of the
shoots and the roots
once these organs are produced in the tips
tips
they then dissolve in the solution of
the cells
and diffuse backwards along the shoot or
the root
in the shoots these auxin stimulate growth
growth
causing the shoots to grow
but in their roots they do the opposite
the two responses we're gonna cover are phototropism
phototropism
which is a response to light
and geotropism which is a response to gravity
gravity
and you might also hear this be called gravitropism
gravitropism
now the key rules that you need to remember
remember
are that once the auctions are produced
in the tips and they diffuse along
they'll always accumulate on a shaded
side rather than a sunny side
and the lower side rather than the upper side
if we start with the shoots
we can say that they're positively phototropic
phototropic
meaning that they grow towards the light
but that they're negatively geotropic
because they grow away from the ground
so the opposite direction to gravity
to see how this works let's take a look
at this shoot
because the sun is on its left in this image
image
the right side will be in the shade
and so the auxin will accumulate on the right
right
and because auxin stimulate growth in shoots
shoots
it causes these cells on the shaded side
to grow faster than on the sunny side
and as you can see it's this difference
in growth rate that causes the shoot to
curve around towards the light
because these cells on the right hand
side are growing lots
but the cells on the left aren't growing
if we take this shoot instead
we can see gravity will have exactly the
same effect
the auxin will collect on the lower side here
here
so the cells on this side grow faster
than the top side
now the roots are basically just the opposite
opposite
negatively phototropic
and positively gravitropic
so grow away from the light
and down towards the ground
normally all the plant roots will be
underground so don't detect any light
but if they do happen to get exposed to
light for some reason
then the auxins will accumulate on the
lower shaded side
and remember that in the roots auxins
inhibit growth so the upper side will
grow faster and cause the root to curve downwards
now if we pretend for a second that it
curves to the left a bit more so that
it's all horizontal
we can use this to think about the
effect for gravity
the auxins are going to accumulate on
the lower side
and they're going to inhibit growth
so this means that the upper side will
grow faster
anyways that's everything for this video
so hope you found that useful
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