By: J. Nixon Jude
Grade 9 IGCSE
Biology student
Transport in
plants
Xylem
Transports water and minerals
Provides support to the plant
Xylem vessels structure
No cell contents just a continuous column of water
Cell walls between cells have broken down (top
and bottom walls)
The vessel's walls are thickened by lignin. They
provide support to the plant.
Cells are dead for free passage of water
Root hair cells
Root hairs are single-celled epidermis cells in roots.
Water and dissolved minerals enter from root hairs
by osmosis because soil water has higher potential
than cytoplasm
Structure of root
The root hair increases the surface area and an
increase in surface area results in the increased
rate of absorption of water by osmosis and
mineral ions by active transport.
Pathway taken by water
Osmosis causes water to pass into root hair cells,
through the root cortex to the xylem. Water enters root hair because
it has lower water potential than root hair cell.
Root hair cell > Root cortex > Xylem > Leaf mesophyll cells
If you put a celery stalk in water and food color to
the water after some hours the green leaf will have some
change colour and the xylem vessels will be stained.
TRANSPIRATION
Through Xylem water travels up to the leaves
to replace the water lost by transpiration
Transpiration is loss of water vapour from
leaves by evaporation of watre at the surface
of the mesophyll cells followed by diffusion
of water vapour through the stomata.
Investigation in transpiration
We cut a root plant underwater
Fill it in the sealed mouth of a
potometer.
Introduce an air bubble in the water
channel
There is a suction towards beaker due
to transpiration, resulting in the
movement of bubble.
Transpiration stream
Water vapour loss
Evaporation takes place from the surface of spongy
mesophyll cell.
The many interconnecting air spaces between these cells
and the stomata creatwes a large surface area.
This helps in rapid evaporation when stoma is open.
Xylem adaptations
Lignin deposits in cell walls which make xylem cells
die.
These cells then become hollow when they lose
organelles and cytoplasm and join end to end as a
continous tube of water and mineral ions
Lignin strengthens structure of plant
Movement s unidirectional.
Transpiration pathway
Xylem vessels < spongy mesophyll cells < Guard cell, stoma
Transpiration Functions
Transporting mineral ions
Providing water to keep cells turgid
Providing water to leaf cells foe photosynthesis
Keeping leaves cool, conversion of water to water vapour as
plant, uses up heat to convert water into water vapouir.
Transpiration stream
Water molecules are attracted to each other
by cohesion.
Water moves as a continuous transpiration
stream.
There is a pull to xylem from leaves due to
transpiration.
Each water molecule pulls next one due to
cohesion.
The faster the transpiration the faster the molecules are pulled up through xylem.
Effects on temperature, wind, humidity
Wind speed
Transpiration rate increases with wind speed as it removes water vapour from the
leaf.
Humidity
Transpiration decreases when humidity increases because of more concentration of
water vapour in the air.
Temperature
It increases when temperature increases because of high kinetic energy in particles.
Wilting
When there is less water in soil than the water
transpired, the cells and cell wall becomes weak
resulting in collapsing of the plant
Translocation
It is the transport of amino acids and sucrose
through phloem. Cells are joined end to end. The
end has a sieve plate. Particles move in both
directions. It moves from source to sink.
Leaves > roots and storage organs
source
sink
In winter, when there are no leaves,
sink becomes source and it transports
wherever there is need so that it can continue
respiration and,
In summer, this happens again
THANK YOU!