Transport in Plants

Transport in Plants
Phloem
Adaptations
Holes in the sieve plates allows flow of the food
substance (mainly sucrose) through sieve tube cells.
Functions
Transports food from the
leaves to rest of the plant
The sucrose,
amnio acids
are also stored
in fruits.
Structure
Has Sieve Cells which allow the
food (Sucrose) using osmosis.
Companion Cells help in providing the energy for
the sieve cells as the transportation of the food
requires energy.
Transpiration
Means: Loss of water vapour from
aerial parts of the plant, especially
through the stomata of the leaves
Dependent upon evaporation.
Factors affecting Transpiration
Humidity of air
More Humid, slower rate of transpiration
Temperature of air
Higher temperature -> increases
rate of evaporation of water vapor ->
Transpiration is greater
Strong Wind
Stronger Wind, higher rate of transpiration
Light
Affects the size of stomata -> presence
of light = increase of transpiration
Transpiration Pull: As a result of transpiration,
water moves up the whole column from the
roots to the leaf. This is also how water get
transported up the plant. The plant has to
loose water to gain water.
Importance of transpiration : WILTING
What is wilting?
Leaf folds up because of
excessive loss of water
Advantages
Rate of transpiration reduced
Leaf folds up to
reduce surface
exposed to sunlight
Causes guard cells to become flaccid
(stomata will close) to prevent water lost
Disadvantages
Rate of photosynthesis
is reduced
Water becomes a
limiting factor
Closed stomata cause the
amount of carbon dioxide
entering the leaf to reduce.
Xylem
Structure
Walls made of lignin
Consists of mainly vessels
It has pits which allow
water and dissolved
minerals to be
transported sideways
to other cells.
Stretches from roots to leaves
Adaptations
It has lignified walls to support the plant
It has a hollow lumen with no cross
walls to let water pass through it easily
It is a dead structure with no
protoplasm (hollow lumen)
Functions
Provide mechanical support for the plant
Transport water from the roots to the rest of the plant
Movement of water
Water enters the plant through
the roots through osmosis
Cell sap in root hair has lower water
potential than the surrounding soil
solution. Therefore, water has to enter
through osmosis (water flow from higher
water potential to lower water potential)
Water passes by osmosis from the
root hair cell to the inner cells.
This process continues until the
water reaches the xylem vessels
to be transported throughout the
plant
Manufactured Food Substances
Transported as sucrose and amino acids
Translocation is an active process that requires
energy (Not fully understood)
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