Hello everyone
previously in the chapter of plant tissues
we have discussed some specialized tissues
needed by the plant to carry out functions
like growth, photosynthesis etc and we have
also seen the tissues that provide support
to the plant during adverse conditions like
storm. Along with these functions, a very
important function of the plant is the circulation
or transport of food and water to all the
parts of the plant which includes the highest
or lowest part of that plant. But unlike humans
and animals
plants lack a circulatory system which involves
(blood, veins, artery) to provide nutrients
to all its parts so what is it that makes
them transport food and water to the entire
plant body??? they have a specialized form
of tissue to carry out this function called
the vascular tissue which is nothing but a
conducting or a transporting tissue
Like any other living organism plants will
also have the same requirements of food and
water to live. Each and every part of that
tree requires food and water.
Talking about food by now we know that plants
prepare their own food through a process called
photosynthesis but what about water?? from
where do they get their required water?
Lets look at the water transport system in
a plant..
Water transport:
Rain water that falls on the plant (leaves,
stem etc) will not be absorbed by the plant
as the plant has a waterproof coating on its
entire plant surface called as epidermis (previously
studied). So water that falls on the ground
is absorbed by the roots of the plant and
then supplied to all the parts of the plant
many a times people water their house hold
plant by pouring water on the top of the plant
this may help in keeping the plant fresh and
clean but It doesn t fulfill the plants need
for water so now we know that we must water
the plant close to the roots this may also
help in reducing water wastage.
but the main question here is how does the
water that is absorbed by the roots in the
lower most portion of the plant get transported
to the various parts of the plant and that
too against gravity ????
To perform this important function plants
have a tissue which is made up of different
types of cells which by now we know it is
a complex tissue. In comparison to this we
have discussed a tissue named parenchyma which
we said was a simple tissue as it was made
up of just one type of cells.
The function of this tissue can be considered
to be similar to the pipelines of a building
which carry water that is stored in the tank
below up to the many apartments against gravity.
The tissue with a similar function in any
plant is called as xylem (word orgin from
xylos= wood) and it will be present where
transporting of water is required. Considering
this tree, it will mainly be present in the
wooden part (stem and branches) which serves
as the transporting medium for water to travel
from the roots to the leaves.
Water will also reach the topmost leaf and
all parts of that leaf as xylem is also present
in the midrib of the leaf this complex tissue
named xylem is made up of 4 different types
of cells lets look at them one by one in detail
1) Vessels
2) Trachieds
3) Xylem parenchyma
4) Xylem fibres
Vessels are most important cells in this type
of tissue. They are like a row of cells placed
end to end which are specialized in performing
the function of water transport. So you must
be wondering what about the other three types
of cells
The tracheids are long cells tapering at both
ends. These cells not only aid in water transport
but because of their structure they also provide
support to the plant.
If you remember we have said that parenchyma
stores food so the xylem parenchyma also performs
the same function of food storage.
And lastly xylem fibres, these cells provide
support to the tissue as well as the plant.
Here we have completed looking at how water
is transported from the roots to all the parts
of the plant.
But what do you think all this water that
is absorbed by the plant is permanently stored
in the plant because of the sun s heat.. excess
of water in the plant is lost by the leaf
surface in the form of water vapor in a process
called transpiration. So indirectly it is
this transpiration process that creates a
suction force that helps the roots to pull
water from the ground and thus transporting
it to all the parts of the plant. If the amount
of water lost by the plant is more than the
amount of water that can be absorbed by the
roots the plants get dehydrated which results
in wilting and death of the plant but only
lack of water may not be cause of death in
a plant. Excessive amnt of water in the soil
i.e over clogging of water near the roots
can result in death 
of the plant.
But besides water plant also requires food
to survive. In a plant the green part (the
leaves) make food for the plant, with the
help of the green pigment called chlorophyll,
sunlight, air and water. All the food made
by the leaves have to reach to all parts of
the plant right?? The food made in the leaves
will be transported to all the parts including
the lowest part of the plant that is the root
cells as they need energy to absorb water
from 
the ground.
The food in the form of sugar which is made
in the leaves is transported with the help
of another type of complex tissue called phloem.
Again since it is a complex tissue it is made
up of 4 different types of cells.
1) Sieve tubes
2) Companion cells
3) Phloem parenchyma
4) Phloem fibres
The most important type of cells in this type
of tissue are the sieve tubes which are attached
from end to end just as the name suggests
sieve means something with perforations. And
because of these perforations sugars are transported
all throughout the plant body.
To accompany them in this same function are
the companion cells arranged next to the sieve
tubes.
All the food is stored in phloem parenchyma
and along with storage it also transports
food in the horizontal direction to the neighboring
cells (lateral transport).
And the support to this tissue is obtained
from phloem fibres which offer mechanical
strength to the plant.
So we have seen how food and water is transported
in all parts of the plant next time when u
see a plant take a moment and observe it and
appreciate this amazing function performed
