Transport of materials
in the Flowering Plant
Contents
Question
Answer
Uptake and transport of
water
Transpiration
Structure of stomata
Root Pressure
Cohesion-Tension Model of
Water Transport in Xylem
Uptake and transport of
- Minerals
- Carbon dioxide
- Photosynthetic products
Modified Plant Food Storage
Organs
Modified Root
Modified Stem
Modified Leaf
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Question
Why do plants need a transport system?
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Answer
To transport water from … to …,
food from … to …,
minerals from … to …,
gases (? and ?) from … to …and
plant growth regulators from … to …
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Materials needed for …
Plants are autotrophic i.e. …
Water, food, minerals, CO2, O2 etc. needed for
metabolic reactions e.g. photosynthesis and
respiration, growth and reproduction
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Uptake and transport of water
Water taken in at roots
Absorbed through root hairs (large surface
area, numerous and no cuticle) by osmosis
Diffuses across the cortex from cell to cell and
into the xylem
Up the xylem vessels (continuous hollow
pipeline) in the stem and out into the leaves
From the leaves, through the stomata into the
atmosphere as water vapour
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Movement
of water
through a
plant
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Transpiration
is the loss of water vapour from the leaves of
a plant
Water lost from cells of leaf
Cells become less turgid
Causes water to move into them from the
xylem vessels
Water is ‘pulled’ up the stem from the roots
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Control of Transpiration
is by the presence of a waxy cuticle on the
leaves and
by the opening and closing of the stomata
Open by day – higher transpiration
Closed at night – transpiration decreases
Controlled by changes in the water content of
the guard cells
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Structure of
stomata
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Root Pressure
The transport of water up through the xylem is
helped by root pressure generated by water
entering the root cells by osmosis which
pushes the water up the xylem.
Does not explain how water gets to the top of
tallest plants
Water rises as a result of a ‘push’ from below
(root pressure) and a ‘pull’ from above
(transpiration)
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Cohesion-Tension Model of
Water Transport in Xylem
(1/3)
= Dixon-Joly Theory. Most acceptable theory
- based on cohesive forces of water
i.e. the force of attraction between water
molecules is great enough to maintain a
continuous unbroken column of water
and the adhesive forces of water molecules
allowing water to ‘stick’ to the walls of the
xylem vessels
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Cohesion-Tension Model of
Water Transport in Xylem
(2/3)
a) leaf cells lose water by evaporation to the
atmosphere.
b) These cells lose turgidity and draw more
water from surrounding cells to try and
maintain turgidity.
c) This results in the formation of a suction
pressure from air spaces to xylem vessels.
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Cohesion-Tension Model of
Water Transport in Xylem
(3/3)
d) Cells closest to the xylem vessels absorb
water from the xylem by osmosis.
e) This creates a tension / pull on the water
in the xylem and draws the water upwards.
f) The water is held at the top of the xylem
by the adhesion of water molecules to the
xylem wall.
Dixon & Joly TCD 1895
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CohesionTension
model
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Uptake and transport of minerals
Minerals are absorbed as ions e.g. magnesium as
Mg ++, nitrogen as nitrate, NO3¯
They enter the root hairs dissolved in water by
active transport
They are transported from the roots to all parts
of the plant by the same route as water
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Uptake and transport of carbon
dioxide
Carbon dioxide can be obtained directly from
respiring cells or
enter the leaves by diffusion through the open
stomata
Needed for …
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Uptake and transport of
photosynthetic products
The products are glucose and oxygen.
glucose – may be stored as starch in the leaf
or transported in the form of sucrose to any
part of the plant that needs it
Transported in the phloem sieve tubes –
energy required – aka translocation
oxygen – used in respiration or released
through stomata by diffusion
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Modified Plant Food Storage
Organs
Many plants store food from the end of one
growing season to the beginning of the next
in order to complete their life cycle.
This is called perennation.
The food is stored in perennating organs
which can be modified root, stem or leaf.
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How plants store food to survive the winter
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Modified Root
In some plants e.g. dicots, the first root grows
straight down to form the main root of the
plant
Forms a tap root
May become swollen with starch
e.g. turnip, carrot, dandelion
or sucrose e.g. sugar beet
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Tap root
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Modified Stem
Underground stems enlarge with food stores
called stem tubers
e.g. potato.
The ‘eyes’ are buds
Buds are only found on stems
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Stem tuber
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Modified Leaf
Swollen leaves that store food e.g. onion,
tulip, daffodil
These are called bulbs
In celery and rhubarb it is the leaf petiole that
is modified for food storage
Many of these food storage organs are also
used in asexual reproduction by the plants.
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Bulb
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END
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