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