Transpiration Video Lecture | Science & Technology for UPSC CSE

transpiration in plants all plants from
the smallest weed to the tallest tree
which is several meters tall need water
plants are not mobile how do they manage
to get water right up to the tallest
branch the roots of plants absorb water
and mineral salts from the soil through
the root hairs by the process of osmosis
only a small percentage of this water is
used by the plant the rest gets
evaporated from the surface of leaves
this evaporation of water from the plant
is called transpiration
let us perform a simple experiment to
show that transpiration takes place in
plants take a medium-sized well watered
potted plant cover it with a transparent
polythene bag a and tie its mouth at the
base of the stem next to the potted
plant place an empty polythene bag B
with its mouth tied expose this setup to
sunlight for an hour or two drops of
water will appear on the inner side of
the bag a the polythene bag B will not
show any water drops in it the leaves
give off water vapor and due to
condensation of the water vapor tiny
drops of water get collected this
experiment shows that plants give out
water to the atmosphere through
transpiration
there are three types of transpiration
depending on the site of transpiration
they are stomatal transpiration
lenticular transpiration and cuticular
transpiration
stomatal transpiration stomata are
openings on the leaf surface through
which transpiration takes place the
stomata are surrounded by guard cells
which help the stomata to open and close
lenticular transpiration lenticels are
minut openings on the stem and a small
amount of water is evaporated through
them lenticels are less in number
compared to the stomata
cuticular transpiration this is the
transpiration which takes place from the
leaf surface leaves are covered by a
waxy layer of cuticle the cuticle
actually helps the leaf to reduce the
amount of transpiration taking place
water is absorbed by the root of a plant
the tiny root hairs help in absorption
the water is then conducted to the upper
parts of the plant through the xylem the
xylem cells have thick walls and can be
compared to the pipes carrying water
from the underground tank to all parts
of the house the mesophyll cells in the
leaf have large intercellular spaces
between them the evaporated water vapor
collects here and goes out through the
stomata which open and close
periodically water is also evaporated
from the surface of the leaf through the
cuticle when the water from the
outermost layer gets evaporated it
absorbs water from the layer of cells
below it and this process creates a pull
by which water gets pulled up through
the xylem transpiration is very
important to plants as the transpiration
pool helps in water rising to the leaves
against the force of gravity
this activity will show us that both
surfaces of the leaf do not transpire at
the same rate we use cobalt chloride
paper to test for the presence of water
cobalt chloride paper which is normally
blue turns pink when it comes in contact
with water
take two strips of cobalt chloride paper
and place them on either surface of one
of the leaves of a potted plant cover
them with a glass slide and hold them in
place with elastic bands leave it for an
hour now remove the strips and observe
them closely what do you see the strip
placed on the lowest surface turns more
pink than that on the upper surface
this shows that transpiration is more on
the under surface than on the upper
surface do you know the reason for this
the upper surface gets more sunlight and
the plant would lose most of its water
if the number of stomata on both the
surfaces were the same though
transpiration is essential for plants
they also adapt themselves to minimize
the water loss through transpiration