Transpiration is the process by which plants absorb water through their roots and release water vapor through pores in their leaves. It serves two main functions: cooling the plant and pumping water and minerals to the leaves for photosynthesis. The majority (80-90%) of water loss from plants occurs through stomatal transpiration, which takes place through specialized pores called stomata located mostly on the undersides of leaves. Transpiration is important as it creates suction that draws water up from the roots and cools the plant through evaporative cooling.

1. TRANSPIRATION
ALI HASSAN VIRK

2. TRANSPIRATIO
N
TRANSPIRATION IS THE
PROCESS WHERE
PLANTS ABSORB WATER
THROUGH THE ROOTS
AND THEN GIVE OFF
WATER VAPOR THROUGH
PORES IN THEIR LEAVES.
AN EXAMPLE
OF TRANSPIRATION IS
WHEN A PLANT ABSORBS
WATER IN ITS ROOTS.

3. ROLE OF
TRANSPIRATION
THE WATER, WARMED BY THE
SUN, TURNS INTO VAPOR
(EVAPORATES), AND PASSES OUT
THROUGH THOUSANDS OF TINY
PORES (STOMATA) MOSTLY ON
THE UNDERSIDE OF THE LEAF
SURFACE. THIS
IS TRANSPIRATION. IT HAS TWO
MAIN FUNCTIONS: COOLING
THE PLANT AND PUMPING WATER
AND MINERALS TO THE LEAVES
FOR PHOTOSYNTHESIS.

4. THREE MAJOR TYPES OF
TRANSPIRATION
CUTICULAR TRANSPIRATION:
CUTICLE IS AN IMPERMEABLE
COVERING PRESENT ON THE
LEAVES AND STEM. IT
CAUSES ONLY AROUND 20%
TRANSPIRATION IN PLANTS
.IT IS FURTHER REDUCED
DUE TO A THICKER CUTICLE
IN XEROPHYTES.

5. LENTICULAR TRANSPIRATION
SOMETIMES WATER MAY EVAPORATE
THROUGH CERTAIN OTHER OPENINGS
PRESENT ON THE OLDER STEMS. THESE
OPENINGS ARE CALLED LENTICELS
AND THE TRANSPIRATION THAT
TAKES PLACE THROUGH TERM IS
KNOWN AS LENTICULAR
TRANSPIRATION.

6. STOMATAL TRANSPIRATION
STOMATAL
TRANSPIRATION: IT IS
THE LOSS OF WATER
THROUGH SPECIALIZED
PORES IN THE LEAVES. IT
ACCOUNTS FOR AROUND
80 TO 90% OF THE
TOTAL WATER LOSS
FROM THE PLANTS.

7. STARCH –SUGAR HYPOTHESIS
STARCH -
SUGAR INTERCONVERSION HYPOTHESIS OF
STOMATA OPENING AND CLOSING. ... DUE
TO THIS HIGH PH, THE STARCH PRODUCED
IN THE NIGHT IS CONVERTED
INTO SUGAR IN THE PRESENCE OF ENZYME
PHOSPHORYLASE. SUGAR IS SOLUBLE IN
WATER AND CONSEQUENTLY INCREASES TO
THE OP OF THE GUARD CELLS. THEREFORE,
THE CELLS BECOME TURGID.

8. STRUCTURE OF STOMATA
• STOMATA ARE THE TINY PORES PRESENT IN THE
EPIDERMAL SURFACE OF LEAVES. THE PORES ARE
GUARDED BY TWO KIDNEY-SHAPED CELLS KNOWN AS
GUARD CELLS. THE INNER WALL OF GUARD CELL
TOWARDS THE STOMATA IS THICKER AS COMPARED
TO THE OUTER WALLS. ALSO, THE PECULIAR
ARRANGEMENT OF THE MICROFIBRILS OF THE GUARD
CELLS ALSO AIDS IN OPENING AND CLOSING OF THE
STOMATAL APERTURE. HE MICROFIBRILS ARE ORIENTED
RADIALLY RATHER THAN LONGITUDINAL. THIS HELP
STOMATA TO OPEN EASILY. IN A DORSIVENTRAL
DICOTYLEDONOUS LEAF, THE NUMBER OF STOMATA IS
A GREATER ON THE LOWER SURFACE AS COMPARED TO
THE UPPER SURFACE. THIS ADAPTATION HELPS IN
REDUCING THE LOSS OF WATER. IN ISOBILATERAL LEAF
IN A MONOCOTYLEDONOUS PLANT, THE NUMBER OF

9. GNIFICANCE OF TRANSPIRATION
TRANSPIRATION IS ESSENTIAL
IN THE LIFE OF LAND PLANTS.
IT HELPS IN THE ABSORPTION
OF CARBON DIOXIDE (CO J
FROM THE ATMOSPHERE
DURING PHOTOSYNTHESIS AS
THE OPENINGS OF STOMATA IN
DAY TIME FACILITATE GASEOUS
EXCHANGE. COOLING EFFECT:
THE LEAVES ABSORB THE
RADIANT ENERGY.

10. ENVIRONMENTAL FACTORS THAT AFFECT
THE RATE OF TRANSPIRATION
• TEMPERATURE
• WITH THE INCREASE IN ATMOSPHERIC TEMPERATURE, THE RATE OF
TRANSPIRATION ALSO INCREASES. THIS IS NOT ONLY BECAUSE EVAPORATION
OCCURS QUICKLY IN WARMER AIR BUT ALSO BECAUSE WARM AIR IS CAPABLE OF
HOLDING MORE WATER VAPORS THAN THE COLD AIR.
• . LIGHT:
• THE RATE OF TRANSPIRATION IS ROUGHLY PROPORTIONAL TO THE INTENSITY
OF LIGHT. THE MODE OF ACTION OF LIGHT IS BOTH DIRECT AND INDIRECT. THE
INCREASING LIGHT INTENSITY RAISES THE TEMPERATURE OF LEAF CELLS AND
THUS INCREASES THE RATE AT WHICH LIQUID WATER IS TRANSFORMED INTO
VAPORS.

11. 4. WIND
WHEN THERE IS NO BREEZE, THE AIR
SURROUNDING A LEAF BECOMES INCREASINGLY
HUMID THUS REDUCING THE RATE OF
TRANSPIRATION. WHEN A BREEZE IS PRESENT, THE
HUMID AIR IS CARRIED AWAY AND REPLACED BY
DRIER AIR.
5. SOIL WATER
A PLANT CANNOT CONTINUE TO TRANSPIRE
RAPIDLY IF ITS WATER LOSS IS NOT MADE UP BY
REPLACEMENT FROM THE SOIL. WHEN ABSORPTION
OF WATER BY THE ROOTS FAILS TO KEEP UP WITH
THE RATE OF TRANSPIRATION, LOSS
OF TURGOR OCCURS, AND THE STOMATA CLOSE.
THIS IMMEDIATELY REDUCES THE RATE OF
TRANSPIRATION (AS WELL AS OF
PHOTOSYNTHESIS). IF THE LOSS OF TURGOR
EXTENDS TO THE REST OF THE LEAF AND STEM, THE
PLANT WILTS.

12. IMPORTANCE OF
TRANSPIRATION
THE PROCESS OF TRANSPIRATION IS A
VERY IMPORTANT PROCEDURE FOR
PLANTS.
IT CREATES A NEGATIVE PRESSURE
GRADIENT THAT HELPS DRAW WATER
AND MINERALS UP THROUGH THE
PLANT FROM ITS ROOTS
HELPS TO KEEP THE PLANT COOL
ON HOT WEATHER - A METHOD OF
EVAPORATIVE COOLING.