We already know about transportation in
 
humans.
 
So what about transportation in plants?
 
Now we know that plants make the food in
 
their leaves and for doing that they
 
require sunlight, chlorophyll, carbon
 
dioxide and water. Plants absorb this
 
water through the soil by the roots, so
 
have you ever wondered how to this plant
 
transfer this water that is absorbed by
 
the roots to their leaves? If the distance
 
between the organs in contact with the
 
soil that is roots and the chlorophyll
 
containing organs, that is leaves is
 
small, then water can be transferred from
 
the roots to the leaves by simple
 
diffusion. But this distance is very
 
large in tall plants. So for such plants
 
plants have transportation system in
 
them. In this lesson we study
 
transportation system in plants in
 
detail. As i just mentioned that plants
 
need to transport water from the roots
 
to the leaves. Now plants do so with the
 
help of a transportation tissue. This
 
tissue which is used to transport water
 
and dissolved minerals is known as
 
xylem tissue. The xylem tissue consists
 
of two types of cells; vessels and tracheids.
 
These are elongated cells which form a
 
continuous column for water conduction.
 
Now as water has to move from the roots
 
up to the leaves that is water has to
 
move against the gravity, so how does
 
water move against the gravity? Inside
 
the xylem tissue to move water up the
 
xylem tissue some pressure or suction is
 
required. So plant does this by two ways.
 
First by root pressure, our second by
 
transpiration pull. Let's first see how
 
water moves up by root pressure? The root
 
cells in contact with the soil take up
 
the ions, so as a result now root cells
 
have more ions
 
and less water in them, while soil
 
particles have more water and less
 
ions in them. So as a result water
 
moves from the area of high
 
concentration to the area of its low
 
concentration; that is water moves from
 
soil particles to the roots. This
 
movement of water from the area of high
 
concentration to low concentration is
 
known as osmosis. Now this difference of
 
water and ions is carried out throughout
 
the water column and thus the water is
 
transported from the roots to the leaves.
 
But this pressure is not enough to carry
 
water in tall plants, so in such plants
 
plants follow some other mechanism that
 
is transpiration pull to carry water
 
from the roots to their leaves. Now to
 
understand what is transpiration pull
 
let's first understand what is
 
transpiration. The loss of water in form
 
of water vapor from all the aerial parts
 
of the plant that is leaves, stem and
 
flower is known as transpiration.
 
Traspiration in leaves mainly occur
 
through stomata. Now due to the loss of
 
water molecules from all the aerial
 
parts of the plant, these parts are left
 
with less water in them. As a result this
 
creates suction and because of this
 
sunction water is pulled upwards from the
 
xylem cells of the roots to the leaves.
 
This is very much similar to the way we suck
 
drinks with the straw. Now
 
transpiration is very essential for the
 
plants because it helps in absorbing
 
nutrients from the soil.
 
Moreover transpiration also helps in
 
regulating the temperature in the plant.
 
So now after seeing both the methods
 
that is root pressure and transpiration
 
pull, Can you tell me that which method
 
is more prevalent during the daytime
 
and which method is more prevalent
 
during the night  time? It's very easy to
 
guess, as we know that transpiration
 
occurs in plants during daytime, so
 
transpiration pull occurs during daytime
 
and root pressure is more prevalent
 
during night time. As we all know that
 
plants also need energy. Plants derive this
 
energy from the food that they
 
synthesize during the process of
 
photosynthesis. Now there should be some
 
method by which they can transport this
 
food that they synthesize in their leaves to
 
the other parts of the plant. This
 
transportation of food and the soluble
 
products of photosynthesis is known as
 
translocation. Food is stored in the
 
plants in the form of sucrose, so plants
 
transfer sucrose all over their body.
 
The tissue responsible for the
 
transport of food is phloem tissue.
 
This phloem tissue has two types of
 
cells. Sieve tube and companion cells. These
 
cells also transport amino acids and
 
other substances in the storage parts of
 
the roots. They also transported to the
 
fruit, seeds and other growing organs. For
 
example sucrose is transported by the
 
phloem tissue to the growing buds as
 
they need energy to grow. This
 
transportation of food through phloem tissue
 
is achieved by using energy from ATP
 
unlike physical forces that are used to
 
transport water through the xylem tisue.
 
Now let's see how food is transported to
 
the phloem tissue? Now when the food is
 
synthesized in the leaves it is to be
 
transported to the seive tubes of the
 
phloem tissue. Now as these sieve tubes
 
are already filled with the food, so this
 
food is transported from low
 
concentration in the leaves to their
 
high concentration in the sieve tubes.
 
This transport requires energy from ATP.
 
Now water from the surroundings xylem
 
cells enter the sieve tubes through
 
osmosis and now from here this food
 
solution is transported to all the parts
 
of the plant. This water serves as the
 
transporting medium in the plants.
 
Similarly as blood serves as the
 
transporting medium food in us. So in
 
this lesson we have seen that water is
 
transported throughout the plant body by
 
xylem tissue and food is transported
 
throughout the plant body by phloem
 
tissue.
 
Let's quickly summarize xylem tissue has
 
two types of cells vessels and tracheids
 
Now there are two ways to transport
 
water from the roots to the leaves by
 
xylem. first root  pressure; second
 
transpiration pull. Similarly phloem
 
tissue has two types of cells sieve tubes
 
and companion cells, but unlike xylem
 
tissue, the phloem tissue uses energy to
 
translocate the food for the plant body.
